AFE5851 www.ti.com SLOS574B – SEPTEMBER 2008 – REVISED MAY 2010 16 CHANNEL VARIABLE GAIN AMPLIFIER (VGA) WITH OCTAL HIGH SPEED ADC Check for Samples: AFE5851 FEATURES 1 • • • • • • • 16 Variable Gain Amplifiers (VGA) – 16 Single-Ended Buffered Inputs With 1VPP Maximum Swing – 5.5nV/√Hz VCA Input Noise (31dB Gain). – Variable Gain –5dB to 31dB With 0.125dB Steps – Digital Gain Control 3rd Order Anti-Aliasing Filter With Programmable Cut-Off Frequency (7.5, 10 and 14MHz). Clamping Analog-to-Digital Converter (ADC) – Octal channel 12-bit, 65 MSPS – 32.5 MSPS Maximum per Input Channel – 2 VGA Outputs Alternately Sampled by Each ADC – Internal and External Reference Support – No External Decoupling Required for References – Serial LVDS Outputs 1.8V and 3.3V Supply 39 mW Total Power per Channel at 32.5 MSPS 64-QFN Package (9mm × 9mm) APPLICATIONS • DESCRIPTION The AFE5851 is an analog front-end targeting applications where the power and level of integration are critical. The device contains 16 variable gain amplifiers (VGA), followed by an octal high speed (up to 65 MSPS) analog to digital converter (ADC). Each of the 16 single ended inputs is buffered, accepts up to 1VPP maximum input swing and it is followed by a VGA with a gain range from –5dB to 31dB. The VGA gain is digitally controlled and the gain curves versus time can be stored in memory, integrated within the device using the serial interface. A selectable clamping and anti-alias low pass filter (with 3dB attenuation at 7.5, 10 or 14MHz) is also integrated between the VGA and ADC for every channel. The VGA/anti-alias filter outputs are differential (limited to 2 VPP) and drive the on-board 12-bit 65MSPS ADC that is shared between two VGAs to optimize the power dissipation. Each VGA output is sampled at alternate clock cycles, making the effective sampling frequency half the input clock rate. The ADC also scales down its power consumption should a lower sampling rate be selected. The ADC outputs are serialized in LVDS streams further minimizing power and board area. The AFE5851 is available in a 64-pin QFN package (9x9mm2) and is specified over the full industrial temperature range (–40°C to 85°C). Imaging: Ultrasound, PET RELATED DEVICES • AFE5801: Octal VGA+ADC, 65 MSPS/channel 1 Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet. PRODUCTION DATA information is current as of publication date. Products conform to specifications per the terms of the Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters. Copyright © 2008–2010, Texas Instruments Incorporated AFE5851 SLOS574B – SEPTEMBER 2008 – REVISED MAY 2010 www.ti.com This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with appropriate precautions. Failure to observe proper handling and installation procedures can cause damage. ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more susceptible to damage because very small parametric changes could cause the device not to meet its published specifications. AVDD3 SDOUT RESET SCLK SDATA SEN PDN VREF_IN TGC SYNC BLOCK DIAGRAM DVDD18 TIME GAIN BLOCK AVDD18 CONTROL VCM SERIAL INTERFACE MEMORY AAF IN1 LVDS VCA1 ADC 1 AAF SERIALIZER D1P D1M IN2 VCA2 AAF IN3 VCA3 AAF ADC 2 SERIALIZER ADC 8 SERIALIZER D2P D2M IN4 VCA4 AAF IN15 VCA15 AAF D8P D8M IN16 VCA16 fADC Clock Divider (by 2) CLKINP fCLKIN /2 FCLKP FCLKM fCLKIN CLKINM PLL AVSS 2 FRAME CLOCK BIT CLOCK DCLKP 6X fCLKIN DCLKM DVSS Submit Documentation Feedback Copyright © 2008–2010, Texas Instruments Incorporated Product Folder Link(s): AFE5851 AFE5851 www.ti.com SLOS574B – SEPTEMBER 2008 – REVISED MAY 2010 DVDD18 D1P D1M 49 DVSS 50 SDOUT 52 51 SEN 53 SDATA 54 SCLK RESET 55 SYNC 57 56 PDN 58 NC 59 AVDD18 AVSS AVSS 60 61 62 63 64 VCM PINOUT (64 pin QFN, 9x9 mm2) 41 DCLKM 9 40 FCLKP IN10 10 39 FCLKM IN11 11 38 D5P IN12 12 37 D5M IN13 13 36 D6P IN14 14 35 D6M IN15 15 34 D7P IN16 16 33 D7M DVSS DVDD18 NC NC VREF_IN AVDD18 AVSS CLKINM CLKINP AVSS 32 8 IN9 D8P IN8 31 DCLKP D8M 42 30 D4M RGC PACKAGE DVDD18 43 7 29 6 IN7 28 IN6 27 D4P 26 44 25 5 24 D3M IN5 23 45 22 4 21 D3P IN4 20 46 19 3 AVDD18 D2M IN3 18 D2P 47 17 48 2 VCM 1 IN2 AVDD3 IN1 PIN FUNCTIONS NAME NUMBER IN1–IN16 1–16 Single-ended analog input pins for channel 1 to 16. CLKINP, CLKINM 21, 22 Differential clock input pins. Single-ended clock also supported (See Clock Inputs Section). VCM 17, 64 Common-mode output pins for possible bias of the analog input signals. VREF_IN 25 Reference input in the external reference mode. RESET 57 Hardware reset pin (active high). SCLK 56 Serial interface clock input. SDATA 55 Serial interface data input. SEN 54 Serial interface enable. SDOUT 53 Serial interface data readout. PDN 59 Global power down control input (active high). SYNC 58 TGC/VGA synchronization signal input D1P/M... D4P/M D5P/M... D8P/M 50... 43 38... 31 LVDS output for channels 1 and 2, 3 and 4, 5 and 6.... to 15 and 16. FCLKM, FCLKP 39, 40 LVDS frame clock output. DCLKM,DCLP 41, 42 LVDS bit clock output. AVDD3 18 3.3V Analog supply voltage. AVDD18 19, 24, 62 1.8V Analog supply voltage. DVDD18 28, 30, 51 1.8V LVDS buffer supply voltage. AVSS 20, 23, 61, 63 Analog ground. DVSS 29, 52 Digital ground. NC 26, 27, 60 Do not connect. Thermal Pad Bottom of the package DESCRIPTION Connect to AVSS. Submit Documentation Feedback Copyright © 2008–2010, Texas Instruments Incorporated Product Folder Link(s): AFE5851 3 AFE5851 SLOS574B – SEPTEMBER 2008 – REVISED MAY 2010 www.ti.com PACKAGING/ORDERING INFORMATION (1) PRODUCT PACKAGELEAD PACKAGE DESIGNATOR SPECIFIED TEMPERATURE RANGE AFE5851 QFN-64 (2) RGC –40°C to 85°C (1) (2) PACKAGE MARKING ORDERING NUMBER TRANSPORT MEDIA, QUANTITY AFE5851 AFE5851IRGCT Tape/Reel, 250 AFE5851 AFE5851IRGCR Tape/Reel, 2000 For the most current package and ordering information, see the Package Option Addendum at the end of this document, or see the TI website at www.ti.com. For the thermal pad size on the package, see the mechanical drawings at the end of this document ABSOLUTE MAXIMUM RATINGS (1) over operating free-air temperature range (unless otherwise noted) RANGE UNIT AVDD3 to AVSS –0.3 to 3.8 V AVDD18 to AVSS –0.3 to 2.2 V DVDD18 to DVSS –0.3 to 2.2 V Voltage between AVSS and DVSS –0.3 to 0.3 V –0.3V to Minimum (3.6, AVDD3+0.3) V VREF_IN to AVSS –0.3 to 2.2 V VCLKP, VCLKM to AVSS –0.3 to 2.2 V Digital control pins to DVSS –0.3 to 2.2 V Analog input pins (INi) to AVSS ESD Human body model TJ Maximum operating junction temperature Tstg Storage temperature range (1) 2 kV 125 °C –60 to 150 °C Stresses above those listed under absolute maximum ratings may cause permanent damage to the device. These are stress ratings only and functional operation of the device at these or any other conditions beyond those indicated under recommended operating conditions is not implied Exposure to absolute maximum rated conditions for extended periods may degrade device reliability THERMAL CHARACTERISTICS over operating free-air temperature range (unless otherwise noted) qJA 0LFM air flow qJC 2 oz. copper trace and pad soldered directly to a JEDEC standard 4-layer 3inch × 3inch PCB TYP UNIT 23.17 °C/W 22.1 °C/W RECOMMENDED OPERATING CONDITIONS PARAMETER TA MIN Ambient Temperature –40 AVDD3 Analog Supply Voltage (VGA) 3.0 AVDD18 Analog Supply Voltage (ADC) 1.7 DVDD18 Digital Supply Voltage (ADC, LVDS) 1.7 TYP MAX UNIT 85 °C 3.3 3.6 V 1.8 1.9 V 1.8 1.9 V VCM+0.5 V 1.45 V SUPPLIES ANALOG INPUTS INi Input voltage VCM–0.5 VREF_IN in external reference mode 1.35 VCM load 1.4 3 mA CLOCK INPUT fCLKIN Input clock frequency 5 fChannel Channel sampling frequency (fCLKIN/2) Input Clock Duty Cycle 4 2.5 40% Submit Documentation Feedback 65 32.5 50% MHz MSPS 60% Copyright © 2008–2010, Texas Instruments Incorporated Product Folder Link(s): AFE5851 AFE5851 www.ti.com SLOS574B – SEPTEMBER 2008 – REVISED MAY 2010 RECOMMENDED OPERATING CONDITIONS (continued) PARAMETER VCLKP–CLKM VCLKP MIN Sine wave, AC-coupled TYP MAX UNIT 0.5 VPP LVPECL, AC-coupled 1.6 VPP LVDS, AC-coupled 0.7 VPP LVCMOS, single-ended, VCLKM connected to AVSS 1.8 VPP 5 pF 100 Ω DIGITAL OUTPUT CLOAD External load capacitance from each output pin to DVSS RLOAD Differential load resistance (external) between the LVDS output pairs ELECTRICAL CHARACTERISTICS Unless otherwise noted, typical values are at 25°C, min and max values are across full temperature range Tmin= –40°C to Tmax=85°C, AVDD3=3.3V, AVDD18=1.8V, DVDD18=1.8V, –1dBFS analog input AC coupled with 0.1mF, internal reference mode, maximum rated channel sampling frequency (32.5 MSPS), LVCMOS (single-ended) clock, 50% duty cycle, anti-aliasing filter set at 14MHz (3dB corner), output clamp disabled and analog high-pass filter enabled. PARAMETER TEST CONDITIONS MIN TYP MAX UNIT VARIABLE GAIN AMPLIFIER (VGA) VCM Max input voltage swing Linear operation Common-mode voltage DC level at the input Gain range Maximum gain – minimum gain 1 Vpp 1.6 V 36 Maximum Gain 29.5 Gain resolution 31 dB 32.5 0.125 or 1 dB Input resistance From input to dc bias level 5 kΩ Input capacitance From input to AVSS 2 pF ANTIALIAS FILTER (AAF) 7.5 MHz filter selected AAF cutoff frequency 10 MHz filter selected 7.5 –3 dB 10 14 MHz filter selected 14 7.5 MHz filter selected 10 MHz filter selected AAF stop-band attenuation 10 –6 dB 14 14 MHz filter selected 18 –12 dB 24 14 MHz filter selected 10 MHz filter selected MHz 30 7.5 MHz filter selected In-band attenuation MHz 20 7.5 MHz filter selected 10 MHz filter selected MHz 1.2 At 3.2 MHz 0.5 14 MHz filter selected dB 0.2 FULL-CHANNEL CHARACTERISTICS Gain matching Across channels and parts +0.1 +0.6 Gain error –5 to 28dB gain –1.2 ±0.3 1.2 Gain > 28dB gain –1.8 ±0.5 1.8 Offset error 31dB gain –50 Input-referred noise voltage 5 MHz, 31dB VGA gain, low-noise mode 5 6.5 5 MHz, 31dB VGA gain, default-noise mode SNR Signal-to-noise ratio HD2 Second-harmonic distortion HD3 Third-harmonic distortion dB 50 5.5 –1dBFS ADC input, 6dB gain dB LSB nV/√Hz 66 –1dBFS ADC input, 17dB VGA gain, fin = 2MHz –48 –55 –1dBFS ADC input, 31dB VGA gain, fin = 2MHz –55 –65 –1dBFS ADC input, 17dB VGA gain, fin = 2MHz –52 –63 –1dBFS ADC input, 31dB VGA gain, fin = 2MHz –48 –58 Submit Documentation Feedback Copyright © 2008–2010, Texas Instruments Incorporated Product Folder Link(s): AFE5851 dBFS dBc dBc 5 AFE5851 SLOS574B – SEPTEMBER 2008 – REVISED MAY 2010 www.ti.com ELECTRICAL CHARACTERISTICS (continued) Unless otherwise noted, typical values are at 25°C, min and max values are across full temperature range Tmin= –40°C to Tmax=85°C, AVDD3=3.3V, AVDD18=1.8V, DVDD18=1.8V, –1dBFS analog input AC coupled with 0.1mF, internal reference mode, maximum rated channel sampling frequency (32.5 MSPS), LVCMOS (single-ended) clock, 50% duty cycle, anti-aliasing filter set at 14MHz (3dB corner), output clamp disabled and analog high-pass filter enabled. PARAMETER TEST CONDITIONS MIN TYP MAX UNIT SFDR Spurious free dynamic range –1dBFS ADC input, 17dB VGA gain, fin = 2MHz 55 dBc THD Total harmonic distortion –1dBFS ADC input, 17dB VGA gain, fin = 2MHz 54 dBc IMD Intermodulation distortion fin1=1MHz, fin2=2MHz, Ain1, in2 = –7dBFS, 30dB VGA gain Group delay variation –70 fin from 100kHz to 14MHz, across gain settings and channels ±3.5 fin from 100kHz to 14MHz, across channels ±1.5 dBFS ns Input overload recovery ≤6dB overload to within 1% 1 Input clock cycles Clamp level After amplification. Clamp enabled by default 3 dB ADC number of bits 12 Aggressor: fin = 2MHz, 1dB below ADC full-scale Victims (channel sharing same ADC): 50Ω to AVSS Crosstalk 65 dB POWER Total power dissipation IAVDD3 AVDD3 Current consumption IAVDD18 AVDD18 Current consumption IDVDD18 Default-noise mode 633 723 Low-noise mode 715 831 4.7 7 Default-noise mode 259 290 Low-noise mode 310 350 81 100 DVDD18 Current consumption Standby mode Power down AC PSRR 64 Full power down mode 5 Power-supply rejection ratio mW mA mA mA mW 30 30 mW dBc DIGITAL CHARACTERISTICS (1) The DC specifications refer to the condition where the digital outputs are not switching, but permanently at a valid logic level 0 or 1. Unless otherwise noted, typical values are at 25°C, min and max values are across full temperature range Tmin= –40°C to Tmax=85°C, AVDD3=3.3V, AVDD18=1.8V, DVDD18=1.8V, external differential load resistance between the LVDS output pair Rload=100Ω. PARAMETER TEST CONDITIONS MIN TYP MAX UNIT DIGITAL INPUTS High-level input voltage 1.4 3.6 Low-level input voltage 0.8 V V High-level input current 10 mA Low-level input current 10 mA 4 pF Input Capacitance DIGITAL OUTPUTS High-level output voltage 1375 Low-level output voltage 1025 Output differential voltage |VOD| Output offset voltage VOS Common-mode voltage of DiP and DiM Output capacitance Output capacitance inside the device, from either output to DVSS (1) 6 mV 270 380 490 0.9 1.15 1.5 2 V pF Note: All LVDS specifications have been characterized but not production tested. Submit Documentation Feedback Copyright © 2008–2010, Texas Instruments Incorporated Product Folder Link(s): AFE5851 AFE5851 www.ti.com SLOS574B – SEPTEMBER 2008 – REVISED MAY 2010 OUTPUT INTERFACE TIMING(1) Typical values are at 25°C, AVDD3 = 3.3V, AVDD18 = DVDD = 1.8V, LVCMOS (single ended) clock, CLOAD = 5pF, RLOAD = 100Ω, IO = 3.5mA, unless otherwise noted. Minimum and maximum values are across the full temperature range TMIN = –40°C to TMAX = 85°C. PARAMETER ta tj TEST CONDITIONS Aperture delay The delay in time between the rising edge of the input sampling clock and the actual time at which the sampling occurs Aperture delay matching Across channels within the same device MIN TYP 0.7 3 Aperture jitter Wake-up time ADC latency tdelay ±150 ps 450 fs rms 10 50 Time to valid data after coming out of PDN GLOBAL mode 50 200 Time to valid data after stopping and restarting the input clock 30 200 Default, after reset 11 3 UNIT ns Time to valid data after coming out of STANDBY mode Input clock rising edge (zero cross) to frame clock rising edge (zero cross) minus half the input clock period (T). tdelay MAX 4.7 ms Input clock cycles 6.4 ns 1 ns Variation At fixed supply and 20°C T difference –1 tRISE tFALL Data rise time Data fall time Rise time measured from –100mV to 100mV Fall time measured from 100mV to –100mV 10 MHz < fCLKIN < 65MHz 0.1 0.25 0.4 ns tFCLKRISE tFCLKFALL Frame clock rise time Frame clock fall time Rise time measured from –100mV to 100mV Fall time measured from 100mV to –100mV 10MHz < fCLKIN < 65MHz 0.1 0.25 0.4 ns Frame clock duty cycle Zero crossing of the rising edge to zero crossing of the falling edge 48 50 52 ns Bit clock rise time Bit clock fall time Rise time measured from –100mV to 100mV Fall time measured from 100mV to –100mV 10MHz < fCLKIN < 65MHz 0.1 0.2 0.35 ns Bit clock duty cycle Zero crossing of the rising edge to zero crossing of the falling edge 10MHz < fCLKIN < 65MHz 44% 50% 56% tDCLKRISE tDCLKFALL Table 1. Output Interface Timing (1) fCLKIN, Input Clock Frequency [2x Channel Sampling frequency] (1) Setup Time (tsu), ns Hold Time (th), ns tpdi = 0.5 × Ts + tdelay, ns Zero-Cross Data to Zero-Cross Clock (both edges) Zero-Cross Clock to Zero-Cross Data (both edges) Input Clock Zero-Cross (rise edge) to Frame Clock Zero-Cross (rise-edge) Period (T) MHz ns 65 15 50 20 0.5 0.8 0.5 0.8 14.6 40 25 0.75 1.05 0.75 1.05 17.04 30 33 1 1.4 1 1.4 21.19 20 50 1.7 2.1 1.7 2.1 29.52 10 100 3.8 4.2 3.8 4.2 54.71 MIN TYP 0.35 0.65 MAX MIN TYP 0.3 0.6 MAX MIN TYP MAX 12.35 See timing diagrams on the following page. Submit Documentation Feedback Copyright © 2008–2010, Texas Instruments Incorporated Product Folder Link(s): AFE5851 7 8 Output Data CHnOUT Data rate = 12 x fCLKIN Bit Clock DCLK Freq = 6 x fCLKIN Frame Clock FCLK Freq = 0.5 x fCLKIN Input Clock CLKIN Freq = fCLKIN Input Signal (Even Channels) Input Signal (Odd Channels) D1 (D10) D13 (D2) D0 (D11) D11 (D0) ta Sample N D9 (D2) D8 (D3) D6 (D5) D5 (D6) D4 (D7) SAMPLE N-5 Channels 2,4,6,8,10,12,14,16 D7 (D4) Data bit in LSB First mode Data bit in MSB First mode D10 (D1) Submit Documentation Feedback Product Folder Link(s): AFE5851 D1 (D10) Bit Clock D2 (D9) Output Data Pair D3 (D8) D0 (D11) Sample N+1 D10 (D1) CHi out tsu DCLKM DCLKP D11 (D0) 11 clock cycles latency Sample N+5 D9 (D2) th D8 (D3) D6 (D5) D5 (D6) D4 (D7) Dn SAMPLE N Channels 2,4,6,8,10,12,14,16 D7 (D4) D2 (D9) Dn+1 D3 (D8) tsu D1 (D10) D0 (D11) tpdi th Sample N+6 D11 (D0) D10 (D1) D9 (D2) D8 (D3) D6 (D5) D5 (D6) D4 (D7) SAMPLE N Channels 1,3,5,7,9,11,13,15 D7 (D4) T D3 (D8) D2 (D9) D1 (D10) D0 (D11) Sample N+6 D10 (D1) SAMPLE N+1 D11 (D0) AFE5851 SLOS574B – SEPTEMBER 2008 – REVISED MAY 2010 www.ti.com Copyright © 2008–2010, Texas Instruments Incorporated AFE5851 www.ti.com SLOS574B – SEPTEMBER 2008 – REVISED MAY 2010 TYPICAL CHARACTERISTICS All graphs are at 25°C, AVDD3 = 3.3V, AVDD18 = DVDD18 = 1.8V, –1dBFS analog input AC coupled with 0.1mF, internal reference mode, maximum rated channel sampling frequency (32.5 MSPS), LVCMOS (single-ended) clock, 50% duty cycle, fIN = 2MHz, anti-aliasing filter set at 14MHz (3dB corner), output clamp disable and analog high-pass filter enabled. spacer 0 0 Ain = -6 dBFS GAIN = 6 dB HD2 = -82.8 dBc HD3 = -80.1 dBc THD = 77.6 dBc SNR = 66.4 dBFS SINAD = 66.3 dBFS SFDR = 80.1 dBc -40 -60 Ain = -1 dBFS GAIN = 30 dB SFDR = 59.3 dBc SNR = 64.5 dBFS SINAD = 58.5 dBFS THD = 58.8 dBc HD2 = -69.3 dBc HD3 = -59.3 dBc -20 Amplitude - dB Amplitude - dB -20 -80 -40 -60 -80 -100 -100 -110 -110 0 2 4 6 8 10 f - Frequency - MHz 12 14 16 18 5 0 Figure 1. FFT for 2MHz Input Signal and 6dB Gain Coarse Gain = 30 dB 27 23 Measured Gain - dB Gain - dB 25 Coarse Gain = 24 dB 21 19 17 15 Coarse Gain = 12 dB 13 11 0 0.125 0.25 0.375 0.5 0.625 0.75 15 20 Figure 2. FFT for 2MHz Input Signal and 30dB Gain 31 29 10 f - Frequency - MHz 0.875 32 30 28 26 24 22 20 18 16 14 12 10 8 6 4 2 0 -2 -4 -6 0 @ -40°C @ 25°C @ 85°C (Ideal+1dB) line (Ideal-1 dB) line 4 8 20 16 Gain code 12 FINE_GAIN Register Setting Figure 3. Fine Gain versus Gain Code 24 28 32 36 Figure 4. Measured Gain versus Gain Code and Temperature 1 170 0.8 Output-Referred Noise - nV/√Hz @ -40°C 0.6 Gain Error - dB 0.4 @ 25°C 0.2 0 -0.2 @ 85°C -0.4 -0.6 150 Low Noise Disabled 130 110 90 Low Noise Enabled 70 -0.8 -1 0 4 8 12 16 20 Gain 24 28 32 36 Figure 5. Gain Error versus Gain Code and Temperature 50 -5 -3 -1 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 Gain - dB Figure 6. Output-Referred Noise versus Gain Submit Documentation Feedback Copyright © 2008–2010, Texas Instruments Incorporated Product Folder Link(s): AFE5851 9 AFE5851 SLOS574B – SEPTEMBER 2008 – REVISED MAY 2010 www.ti.com TYPICAL CHARACTERISTICS (continued) All graphs are at 25°C, AVDD3 = 3.3V, AVDD18 = DVDD18 = 1.8V, –1dBFS analog input AC coupled with 0.1mF, internal reference mode, maximum rated channel sampling frequency (32.5 MSPS), LVCMOS (single-ended) clock, 50% duty cycle, fIN = 2MHz, anti-aliasing filter set at 14MHz (3dB corner), output clamp disable and analog high-pass filter enabled. spacer 13 150 140 12 120 Input-Referred Noise - nV/√Hz Input-Referred Noise - nV/√Hz 130 110 100 90 Low Noise Mode Disabled 80 70 60 50 40 30 Low Noise Mode Enabled 20 10 -6 -4 -2 0 2 11 10 Low Noise Mode Disabled 9 8 7 Low Noise Mode Enabled 6 5 4 6 8 Gain - dB 10 12 14 16 4 17 18 18 19 20 21 22 23 24 25 26 27 28 29 30 31 Gain - dB Figure 7. Input-Referred Noise for Low Gains Figure 8. Input-Referred Noise for High Gains -40 -40 -45 -45 10 MHz, -1dB -50 -50 5 MHz, -6 dB HD2 - dB HD2 - dB 10 MHz, -6 dB -55 5 MHz, -1dB -55 -60 -60 -65 -70 -65 -75 2 MHz, -1dB -70 -80 -75 -80 -5 2 MHz, -6 dB -85 0 5 10 15 Gain - dB 20 25 30 -90 -5 35 Figure 9. HD2 Across Coarse Gain and 3 Fin (–1dBFS) (1) 0 5 10 15 Gain - dB 20 25 30 35 Figure 10. HD2 Across Coarse Gain and 3 Fin (–6dBFS) (2) -50 -50 -52 5 MHz, -1 dB -55 -60 -56 -65 -58 -70 HD3 - dB HD3 - dB 10 MHz, -1 dB -54 -60 -62 -75 -80 2 MHz, -1 dB -64 -85 10 MHz, -1 dB -66 -90 2 MHz, -1 dB 5 MHz, -1 dB -68 -70 -95 -5 0 5 10 15 Gain - dB 20 25 30 35 Figure 11. HD3 Across Coarse Gain and 3 Fin (–1dBFS)(1) (1) (2) 10 -100 -5 0 5 10 15 Gain - dB 20 25 30 35 Figure 12. HD3 Across Coarse Gain and 3 Fin (–6dBFS)(2) For gains ≥5dB, the input amplitude is adjusted to give –1dBFS. At 5dB gain, input amplitude is 4dBm (corresponding to –1dBFS). For gains less than 5dB, the input is kept constant at 4dBm. For gains ≥0dB, the input amplitude is adjusted to give –6dBFS. At 0dB gain, input amplitude is 4dBm (corresponding to –6dBFS). For gains less than 0dB, the input is kept constant at 4dBm. Submit Documentation Feedback Copyright © 2008–2010, Texas Instruments Incorporated Product Folder Link(s): AFE5851 AFE5851 www.ti.com SLOS574B – SEPTEMBER 2008 – REVISED MAY 2010 TYPICAL CHARACTERISTICS (continued) All graphs are at 25°C, AVDD3 = 3.3V, AVDD18 = DVDD18 = 1.8V, –1dBFS analog input AC coupled with 0.1mF, internal reference mode, maximum rated channel sampling frequency (32.5 MSPS), LVCMOS (single-ended) clock, 50% duty cycle, fIN = 2MHz, anti-aliasing filter set at 14MHz (3dB corner), output clamp disable and analog high-pass filter enabled. spacer -30 -30 -40 -40 18 dB Gain -60 24 dB Gain -50 6 dB Gain 6 dB Gain HD3 - dB HD2 - dB -50 24 dB Gain -70 -60 -70 -80 -80 -90 -90 -100 -60 -100 -60 18 dB Gain -50 -40 -30 -20 Output Amplitude - dBFS -10 0 -50 -30 -20 -10 0 Output Amplitude - dBFS Figure 13. HD2 versus Output Amplitude Figure 14. HD3 versus Output Amplitude -40 -40 -45 -45 -50 FIN = 10 MHz FIN = 5 MHz -50 FIN = 5 MHz HD3 - dB -55 HD2 - dB -40 -60 -65 FIN = 10 MHz -55 -60 -70 FIN = 2 MHz FIN = 2 MHz -65 -75 -80 -70 0 0.125 0.25 0.375 0.5 Fine Gain - dB 0.625 0.75 0 0.875 Figure 15. HD2 (at 24 dB Gain) Across Fine Gain 0.125 0.25 0.375 0.5 Fine Gain - dB 0.625 0.75 0.875 Figure 16. HD3 (at 24 dB Gain) Across Fine Gain 2090 -30 -40 2080 Analog HPF Disabled 10 MHz - Adjacent Channel 10 MHz - Shared Channel 2070 10 MHz - Far Channel -60 2 MHz - Shared Channel -70 Output Code dB -50 Analog HPF Enabled 2060 2050 2 MHz - Adjacent Channel -80 Digital HPF Enabled 2040 2 MHz - Far Channel -90 2030 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Channel Figure 17. Crosstalk (3) (3) -5 -3 -1 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 Gain - dB Figure 18. Output Offset Across TGC Gain -1dB signal applied on one channel at a time and output is observed on: 1. Shared channel - second channel in the pair having a common ADC 2. Adjacent channel - channel next to the aggressor channel, but not a shared channel 3. Far channel - all other channels (neither shared or adjacent) Submit Documentation Feedback Copyright © 2008–2010, Texas Instruments Incorporated Product Folder Link(s): AFE5851 11 AFE5851 SLOS574B – SEPTEMBER 2008 – REVISED MAY 2010 www.ti.com TYPICAL CHARACTERISTICS (continued) 1 15 0 10 -1 5 -2 14 MHz Analog Filter K = 10 0 -3 -5 -4 -5 Gain - dB Normalized Amplitude - dB All graphs are at 25°C, AVDD3 = 3.3V, AVDD18 = DVDD18 = 1.8V, –1dBFS analog input AC coupled with 0.1mF, internal reference mode, maximum rated channel sampling frequency (32.5 MSPS), LVCMOS (single-ended) clock, 50% duty cycle, fIN = 2MHz, anti-aliasing filter set at 14MHz (3dB corner), output clamp disable and analog high-pass filter enabled. spacer 10 MHz -6 -7 K=5 K=6 K=7 K=8 K=9 -15 -20 -25 7.5 MHz -8 -10 K=2 K=3 -30 -9 -35 -10 -40 -11 -12 0 1 2 3 4 5 6 -45 0 7 8 9 10 11 12 13 14 15 16 17 18 19 20 fi - Input Frequency - MHz 0.2 Figure 19. Antialiasing Filter Frequency Response 0.58 0.75 0.56 0.725 0.7 AVDD Power, Low Noise Mode 0.52 0.65 0.625 Total Power - W 0.5 0.46 0.44 0.42 0.4 0.8 1 1.2 f - Frequency - MHz 1.4 1.6 1.8 2 Total Power, Low Noise Mode 0.6 0.575 0.55 0.525 0.5 AVDD Power, Default 0.36 0.475 0.34 0.45 Total Power, Default 0.425 0.32 0.3 0 0.6 0.675 0.48 0.38 0.4 Figure 20. Highpass Filter Options 0.54 AVDD3 Power - W K=4 0.4 5 10 15 20 25 30 35 40 45 Clock Frequency - MSPS 50 55 60 65 0 5 10 15 20 25 30 35 40 45 50 55 60 65 Clock Frequency - MSPS Figure 21. Analog Power versus Input Clock Frequency Figure 22. Total Power versus Input Clock Frequency 8 4.5 7 4 Count (Number of Channels) Percent - % 6 5 4 3 2 1 3 2.5 2 1.5 1 0.5 2095 2085 2090 2075 2080 2065 2070 2055 2060 2045 2050 2035 2040 2025 2030 Output Code Figure 23. Gain Matching Measured at a Single Gain (30 dB) as Peak-to-Peak Variation of Gain Across Channels on Every Device and Measured at 3 Temperatures. Every Device at Each Temperature is Counted as One Event. 12 2015 0.49 0.11 0.13 0.15 0.17 0.19 0.21 0.23 0.25 0.27 0.29 0.31 0.33 0.35 0.37 0.39 0.41 0.43 0.45 0.47 Gain Matching - dB 2020 0 0 0.05 0.07 0.09 3.5 2005 2010 Percent % of Occurences Gain = 30 dB Figure 24. Offset (Average Code) with Signal. Every Channel Counted as One Event. Submit Documentation Feedback Copyright © 2008–2010, Texas Instruments Incorporated Product Folder Link(s): AFE5851 AFE5851 www.ti.com SLOS574B – SEPTEMBER 2008 – REVISED MAY 2010 TYPICAL CHARACTERISTICS (continued) All graphs are at 25°C, AVDD3 = 3.3V, AVDD18 = DVDD18 = 1.8V, –1dBFS analog input AC coupled with 0.1mF, internal reference mode, maximum rated channel sampling frequency (32.5 MSPS), LVCMOS (single-ended) clock, 50% duty cycle, fIN = 2MHz, anti-aliasing filter set at 14MHz (3dB corner), output clamp disable and analog high-pass filter enabled. spacer 2800 2600 fIN = 2 MHz Output Code 2400 2200 2000 1800 1600 1400 1200 1000 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500 7000 7500 8000 Sample Figure 25. TGC Sweep with Interpolation Disabled and High-Pass Filter Enabled 2800 2600 fIN = 2 MHz Output Code 2400 2200 2000 1800 1600 1400 1200 1000 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500 7000 7500 8000 Sample Figure 26. TGC Sweep with Interpolation Disabled and High-Pass Filter Disabled 2800 2600 fIN = 2 MHz Output Code 2400 2200 2000 1800 1600 1400 1200 1000 2500 3000 3500 4000 4500 5000 5500 6000 6500 7000 7500 8000 8500 9000 9500 10000 Sample Figure 27. TGC Sweep with Interpolation Enabled and High-Pass Filter Disabled Submit Documentation Feedback Copyright © 2008–2010, Texas Instruments Incorporated Product Folder Link(s): AFE5851 13 AFE5851 SLOS574B – SEPTEMBER 2008 – REVISED MAY 2010 www.ti.com TYPICAL CHARACTERISTICS (continued) All graphs are at 25°C, AVDD3 = 3.3V, AVDD18 = DVDD18 = 1.8V, –1dBFS analog input AC coupled with 0.1mF, internal reference mode, maximum rated channel sampling frequency (32.5 MSPS), LVCMOS (single-ended) clock, 50% duty cycle, fIN = 2MHz, anti-aliasing filter set at 14MHz (3dB corner), output clamp disable and analog high-pass filter enabled. spacer 0 Ain = -7 dBFS each tone Gain = 30 dB IMD3 = -70 dBFS Amplitude - dB -20 -40 -60 -80 -100 -110 0 2 4 6 8 10 f - Frequency - MHz 12 14 16 18 Figure 28. Intermodulation Distortion : 21 19 17 Analog HPA Disabled IRN, nV/√Hz 15 13 Default 11 High Pass Digital Filter K = 4 9 7 5 3 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 f - Frequency - MHz 2.2 2.4 2.6 2.8 3 Figure 29. IRN versus Frequency (Gain = 31dB) DCLK Data Figure 30. LVDS Eye Pattern 14 Submit Documentation Feedback Copyright © 2008–2010, Texas Instruments Incorporated Product Folder Link(s): AFE5851 AFE5851 www.ti.com SLOS574B – SEPTEMBER 2008 – REVISED MAY 2010 APPLICATION INFORMATION THEORY OF OPERATION The AFE5851 is a low power CMOS monolithic analog front end that includes a 16-channel variable gain amplifier (VGA) followed by an 8-channel 12-bit high speed pipeline analog to digital converter (ADC) based on switched capacitor architecture. Each of the 16 VGA single ended inputs is buffered and accepts a maximum swing of 1VPP centered at a DC level (VCM) of about 1.6V. Each VGA has a gain range from –5dB to 31dB and it is digitally controlled, with a resolution of 0.125 dB. The gain curves (common to all VGAs) versus time can be stored in memory integrated within the device using the serial interface. A hardware sync input pin is available (SYNC). When a pulse is applied to this pin, all the VGAs in the device start stepping through the selected time-gain curve at the same clock cycle. This sync can also be initiated by software using the serial interface. A selectable anti-alias low pass filter (AAF) with 6 dB attenuation at 7.5MHz, 10MHz or 14MHz, is also integrated, together with clamping (which can be disabled). The VGA/AAF can output 2VPP differential swing without degradation in the specified linearity, and drive an on-board 12-bit ADC shared between two VGAs to optimize power dissipation. Each VGA output is sampled at the rising edge of alternating clock cycles, making the effective sampling frequency half the input clock rate. For instance, in order to sample each analog channel at 30 MSPS, the input clock frequency needs to be 60 MHz. This effectively introduces a half (sampling) clock delay between the sampling instants of the two analog channels. After the input signals are captured by the sample and hold circuit, the samples are sequentially converted by a series of low resolution stages. The stage outputs are combined in a digital correction logic block to form the final 12-bit word with a latency of 11 clock cycles (without taking into account the delays introduced by the optional digital signal processing functions). The 12-bit words of each channel are serialized and output as LVDS levels in straight offset binary format. In addition to the data streams, a bit clock and frame clock are also output. The frame clock is aligned with the 12-bit word boundary. Notice that for the correct operation of the device (see Serial Interface Section) a positive pulse must be applied to the Reset pin. This sets the internal control registers to zero. There is, nevertheless, no need for any type of power-up sequencing. INPUT CONFIGURATION The analog input for the AFE5851 (Figure 31) consists of an analog buffer input gate biased to a value of 1.6V (usually referred as voltage common mode, VCM). The biasing is done with an internal resistor of 5kΩ. For proper operation, the input signal should be in the recommended input range. The maximum input swing is limited to 1VPP before distortion/saturation of the input stage occurs. As the input DC level (VCM) is about 1.6V, the input of the VGA should stay between 1.1V and 2.1V. If the information in the low frequencies of the signal is irrelevant AC coupling can be used. As the input capacitor forms a high-pass filter with the internal bias resistor (5kΩ), the value of the capacitor should allow the lowest frequency of interest to pass with minimum attenuation. For the typical frequencies used in ultrasound (>1MHz) a value of 10nF or greater is recommended. If DC coupling is preferred, the user can tap the VCM output pins to set the DC level of the input signal. VCM output should be connected to high input impedance circuits as its driving capability is limited. Regardless of the chosen input configuration, a capacitor of 100nF should be connected on each VCM input to AVSS. Submit Documentation Feedback Copyright © 2008–2010, Texas Instruments Incorporated Product Folder Link(s): AFE5851 15 AFE5851 SLOS574B – SEPTEMBER 2008 – REVISED MAY 2010 www.ti.com Ch1 Input INP 5 kW AC Clamp coupling Vcm 5 kW CM buffer Internal Voltage Reference Figure 31. Input Equivalent Circuit SERIAL INTERFACE Register Initialization After power-up, the internal registers must be initialized to the default value (zero). Initialization can be done in one of two ways: 1. Through a hardware reset, by applying a positive pulse in the RESET pin 2. Through a software reset, using the serial interface, by setting the SOFTWARE RESET bit to high. Setting this bit initializes the internal registers to the respective default values (all zeros) and then self-resets the SOFTWARE RESET bit to low. In this case, the RESET pin can stay low (inactive). Reset Timing Typical values at 25°C, min and max values across the full temperature range TMIN = –40°C to TMAX = 85°C, AVDD3 = 3.3V, AVDD18 = DVDD18 = 1.8V unless otherwise noted. PARAMETER CONDITIONS MIN t1 Power-on delay time Delay from power-up of AVDD and LVDD to RESET pulse active t2 Reset pulse width Pulse width of active RESET signal t3 Register write delay time Delay from RESET disable to SEN active tPO Power-up delay time 16 Delay from power-up of AVDD and LVDD to output stable Submit Documentation Feedback TYP MAX UNIT 5 ms 10 ns 25 ns 6.5 ms Copyright © 2008–2010, Texas Instruments Incorporated Product Folder Link(s): AFE5851 AFE5851 www.ti.com SLOS574B – SEPTEMBER 2008 – REVISED MAY 2010 Power Supply AVDD, LVDD t1 RESET t2 t3 SEN T0108-03 Figure 32. Reset Timing Diagram Programming of different modes can be done through the serial interface formed by pins SEN (serial interface enable), SCLK (serial interface clock), SDATA (serial interface data) and RESET. SCLK and SDATA have a pull-down resistor to GND of 100kΩ and SEN has a 100kΩ pullup resistor to DVDD18. Serial shift of bits into the device is enabled when SEN is low. Serial data SDATA is latched at every rising edge of SCLK when SEN is active (low). The serial data is loaded into the register at every 24th SCLK rising edge when SEN is low. If the word length exceeds a multiple of 24 bits, the excess bits are ignored. Data can be loaded in multiple of 24-bit words within a single active SEN pulse (there is an internal counter that counts groups of 24 clocks after the falling edge of SEN). The interface can work with the SCLK frequency from 20 MHz down to low speeds (few Hertz) and even with non-50% duty cycle SCLK. The data is divided into two main portions: a register address (8 bits) and the data itself, to load on the addressed register (16bits). When writing to a register with unused bits, these should be set to 0. The following timing diagram illustrates this process: Start Sequence End Sequence SEN t6 t1 t7 t2 Data Latched on Rising Edge of SCLK SCLK t3 SDATA A7 A6 A5 A4 A3 A2 A1 A0 D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 t4 D0 t5 Figure 33. Serial Interface Register Write Submit Documentation Feedback Copyright © 2008–2010, Texas Instruments Incorporated Product Folder Link(s): AFE5851 17 AFE5851 SLOS574B – SEPTEMBER 2008 – REVISED MAY 2010 www.ti.com Minimum values across the full temperature range, TMIN = –40°C to TMAX = 85°C, AVDD3 = 3.3V, AVDD18 = DVDD18 = 1.8V. PARAMETER DESCRIPTION MIN TYP MAX UNIT t1 SCLK period 50 ns t2 SCLK high time 20 ns t3 SCLK low time 20 ns t4 Data setup time 5 ns t5 Data hold time 5 ns t6 SEN fall to SCLK rise 8 ns t7 Time between last SCLK rising edge to SEN rising edge 8 ns General Purpose Register Map The internal registers can be divided into two groups. A group of registers to control all the general functions and settings of the device, and a bank of registers to control the TGC/gain curves operation. Those two sets of registers overlap in all the address space, except for the address 0 which holds the control of the register bank. One of the bits of this register, TGC_REG_WREN (see table below) is used to access one set of registers or the other. Its default value is zero and gives access to the general purpose registers. The TGC control registers (described after the general purpose registers) can be accessed by writing '1' to TGC_REG_WREN. The following table describes the function of the general purpose registers (when TGC_REGISTER_WREN is zero, default). The address format is "address[bit of the register]": ADDRESS FUNCTION DESCRIPTION 0[2] TGC_REGISTER_WREN 0: Access to general-purpose registers. 1: Access to TGC registers 0[1] REGISTER_READOUT_ENABLE 1: Enables readout of the registers 0[0] SOFTWARE_RESET 1: Resets the device and self-resets the bit to zero 1[13] EXTERNAL_REFERENCE 0: Internal reference. 1: External reference 1[11] LOW_FREQUENCY_NOISE_SUPRESSION 0: No suppression. 1: Suppresses noise at low frequencies and pushes it to fchannel/2 1[10] STDBY 0: Power up. 1: Standby (fast power-up mode) 1[9:2] PDN CHANNEL<7:0> PDN for each individual channel (VCA+ADC). LVDS outputs logic 0. 1[1] OUTPUT_DISABLE 0: Output enabled. 1: Output disabled 1[0] GLOBAL_PDN 0: Power up. 1: Global power down (slow power-up mode) 2[15:13] PATTERN_MODE Pattern modes for serial LVDS. 000: No pattern. 001: Sync. 010: Deskew. 011: Custom reg. 100: All 1s. 101: toggle. 110: All 0s. 111: Ramp 2[11] AVERAGING_ENABLE 0: Default (no averaging). 1: Average two channels to increase SNR. 2[10:3] PDN_LVDS Power down the eight data-output LVDS pairs. 3[14:13] SERIALIZED_DATA_RATE Serialization factor. 00: 12×. 01: 10×. 10: 16×. 11: 14× 3[12] DIGITAL_GAIN_ENABLE 0: Default (no gain). 1: Apply digital gain set by the following registers. 3[8] REGISTER_OFFSET_SUBTRACTION_ENA 0: Default (no subtraction). 1: Subtract offset value set in the corresponding BLE registers. 4[3] DFS Data format select. 0: 2s complement. 1: Offset binary 5[13:0] CUSTOM_PATTERN Custom pattern data for LVDS (PATTERN_MODE = 011) 7[10] VCA_LOW_NOISE_MODE_(INCREASE_P OWER) 0: Low power. 1: Low noise, at the expense of increased power (5mW per channel) 7[8:7] SELF_TEST 00, 10: No self-test. 01: Self-test enabled. 100 mV DC applied to the input of the channels. 11: Self-test enabled. 150 mV DC applied to the input of the channels. 7[3:2] FILTER_BW 00: 14MHz. 01: 10MHz. 10: 7.5MHz. 11: Not used. 7[1] INTERNAL_AC_COUPLING VGA coupling. 0: AC-coupled. 1: DC-coupled 13[15:11] DIG_GAIN1 0dB to 6dB in steps of 0.2dB 13[9:2] OFFSET_CH1 Value to be subtracted from channel 1 14[15:11] DIG_GAIN2 0dB to 6dB in steps of 0.2dB 18 Submit Documentation Feedback Copyright © 2008–2010, Texas Instruments Incorporated Product Folder Link(s): AFE5851 AFE5851 www.ti.com SLOS574B – SEPTEMBER 2008 – REVISED MAY 2010 ADDRESS FUNCTION DESCRIPTION 14[9:2] OFFSET_CH2 Value to be subtracted from channel 2 15[15:11] DIG_GAIN3 0dB to 6dB in steps of 0.2dB 15[9:2] OFFSET_CH3 Value to be subtracted from channel 3 16[15:11] DIG_GAIN4 0dB to 6dB in steps of 0.2dB 16[9:2] OFFSET_CH4 Value to be subtracted from channel 4 17[15:11] DIG_GAIN5 0dB to 6dB in steps of 0.2dB 17[9:2] OFFSET_CH5 Value to be subtracted from channel 5 18[15:11] DIG_GAIN6 0dB to 6dB in steps of 0.2dB 18[9:2] OFFSET_CH6 Value to be subtracted from channel 6 19[15:11] DIG_GAIN7 0dB to 6dB in steps of 0.2dB 19[9:2] OFFSET_CH7 Value to be subtracted from channel 7 20[15:11] DIG_GAIN8 0dB to 6dB in steps of 0.2dB 20[9:2] OFFSET_CH8 Value to be subtracted from channel 8 21[4:1] DIGITAL_HIGH_PASS_FILTER_CORNER_ FREQ_FOR_CHANNELS-1–4 Sets k for the high-pass filter as described in General-Purpose Register Description (k from 2 to 10). 21[0] DIGITAL_HIGH_PASS_FILTER_ENABLE_F 0: No high-pass filter. 1: High-pass filter enabled OR_CHANNELS_1–4 25[15:11] DIG_GAIN15 0dB to 6dB in steps of 0.2dB 25[9:2] OFFSET_CH15 Value to be subtracted from channel 16 26[15:11] DIG_GAIN16 0dB to 6dB in steps of 0.2dB 26[9:2] OFFSET_CH16 Value to be subtracted from channel 15 27[15:11] DIG_GAIN13 0dB to 6dB in steps of 0.2dB 27[9:2] OFFSET_CH13 Value to be subtracted from channel 14 28[15:11] DIG_GAIN14 0dB to 6dB in steps of 0.2dB 28[9:2] OFFSET_CH14 Value to be subtracted from channel 13 29[15:11] DIG_GAIN11 0dB to 6dB in steps of 0.2dB 29[9:2] OFFSET_CH11 Value to be subtracted from channel 12 30[15:11] DIG_GAIN12 0dB to 6dB in steps of 0.2dB 30[9:2] OFFSET_CH12 Value to be subtracted from channel 11 31[15:11] DIG_GAIN9 0dB to 6dB in steps of 0.2dB 31[9:2] OFFSET_CH9 Value to be subtracted from channel 10 32[15:11] DIG_GAIN10 0dB to 6dB in steps of 0.2dB 32[9:2] OFFSET_CH10 Value to be subtracted from channel 9 33[4:1] DIGITAL_HIGH_PASS_FILTER_CORNER_ FREQ_FOR_CHANNELS_5–8 Sets k for the high-pass filter as described in General-Purpose Register Description (k from 2 to 10). 33[0] DIGITAL_HIGH_PASS_FILTER_ENABLE_F 0: No high-pass filter. 1: High-pass filter enabled OR_CHANNELS_5–8 70[14] CLAMP_DISABLE 0: Enabled. 1: Disabled Submit Documentation Feedback Copyright © 2008–2010, Texas Instruments Incorporated Product Folder Link(s): AFE5851 19 AFE5851 SLOS574B – SEPTEMBER 2008 – REVISED MAY 2010 www.ti.com General Purpose Register Description AVERAGING_ENABLE Address: 2[11] When set to one, two samples, corresponding to two different channels on the same pair, are averaged (channel 1 with 3, 2 with 4, 5 with 7, 6 with 8, 9 with 11, 10 with 12, 13 with 15 and 14 with 16). If both channels receive the same input, the net effect is an improvement on SNR. The averaging is performed as: 1. Channel 1 with channel 3 comes out on channel 3 LVDS pair, followed by the average of channels 2 and 4 (on the same pair). 2. Channel 5 with channel 7 comes out on channel 4 LVDS pair, followed by the average of channels 6 and 8 (on the same pair). 3. Channel 9 with channel 11 comes out on channel 5 LVDS pair, followed by the average of channels 10 and 12 (on the same pair). 4. Channel 13 with channel 15 comes out on channel 6 LVDS pair, followed by the average of channels 14 and 16 (on the same pair). CUSTOM_PATTERN Address: 5[13:0] This register stores the code that will be output when PATTERN_MODE equal to '011'. See PATTERN_MODE for more details. DFS Address: 4[3] DFS stands for Data Format Select. The ADC output, by default, is in 2s complement mode. Programming the DFS bit to '1' inverts the MSB, and the output becomes straight offset binary mode. DIGITAL_GAIN_ENABLE Address: 3[12] Setting this bit to ‘1’ applies to each channel I the corresponding gain given by DIG_GAINi<15:11>. The gain is given as 0dB+0.2dB*DIG_GAINi<15:11>. For instance, if DIG_GAIN5<15:11>=3, channel 5 is increased by 0.6dB gain. DIG_GAINi<15:11>=31 produces the same effect as DIG_GAINi<15:11>=30 setting the gain of channel i to 6dB. DIGITAL_HIGH_PASS_FILTER and DIGITAL_HIGH_PASS_FILTER_CORNER_FREQ Address: 21[0] Address: 33[0] Address: 21[4:1] Address: 33[4:1] This group of 4 registers controls the characteristics of a digital high pass transfer function applied to the output data, following the formula: y(n)= 2^k/(2^k +1) [ x(n) –x(n–1) + y(n–1)]. K is set as described by the DIGITAL_HIGH_PASS_FILTER_CORNER_FREQ registers (one for the first 8 channels and one for the second group of 8 channels). EXTERNAL_REFERENCE Address: 1[13] Internal reference mode (default) uses approximately 3mW more power on AVDD (already included in all the specification tables). The AFE5851 can operate in external reference mode by programming EXTERNAL_REFERENCE to '1'. In this mode, drive the VREF_IN pin with 1.4V. Due to the high input impedance of this pin, no special drive capabilities are required. The advantage of using the external reference mode is that multiple AFE5851 units can be made to operate with the same external reference, thereby improving parameters such as gain matching across devices. FILTER_BW Address: 7[3:2] This bit sets the 3dB attenuation frequency for the anti-aliasing filter (AAF). 20 Submit Documentation Feedback Copyright © 2008–2010, Texas Instruments Incorporated Product Folder Link(s): AFE5851 AFE5851 www.ti.com SLOS574B – SEPTEMBER 2008 – REVISED MAY 2010 GLOBAL_PDN Address: 1[0] The Global PDN bit is ORed with the signal in the external PDN pin (59). Hereby, a '1' on this bit shuts down the device completely. INTERNAL_AC_COUPLING Address: 7[1] This bit controls an internal high pass filter, Figure 31, set between the input buffer and the VCA. This filter removes the input offset to avoid its amplification by the TGC. An alternative method is to remove the offset effect on the digital domain, either on the device following the ADC or at the ADC output, by using the DIGITAL HIGH PASS FILTER registers (see above). LOW_FREQUENCY_NOISE_SUPRESSION Address: 0[11] low-frequency noise suppression mode is specifically useful in applications where good noise performance is desired in the frequency band of 0MHz to 1MHz (around DC). Setting this mode shifts the low-frequency noise of the ADC in the AFE5851 to approximately fchannel/2, thereby reducing the noise floor around DC to a much lower value. OUTPUT_DISABLE Address: 1[1] A '1' on this bit sets the outputs into high-impedance state. PATTERN_MODE Address: 2[15:13] AFE5851 can output a variety of test patterns on the LVDS outputs. These test patterns replace the normal ADC data output and help on debugging and synchronization with the device reading the output of the ADC: 1. PATTERN_MODE equal to ‘000’ is the default and disables this test mode, i.e., the output data is the same as the ADC data. 2. PATTERN_MODE equal to ‘001’ (SYNC mode) replaces the normal ADC word by a fixed 111111000000 word. 3. PATTERN_MODE equal to ‘010’ sets the DESKEW mode, where the 12-bit ADC output D<11:0> is replaced with the ‘101010101010’ word, creating a continuous stream of ones and zeros in the data line. The exact sequence (first a zero or a one) depends on power-up. This mode only ensures alternating ones and zeros at the output. 4. PATTERN_MODE equal to ‘011’ will output a constant code set by the bits in CUSTOM_PATTERN<13:0>. Depending on the value of SERIALIZED_DATA_RATE (see below) the output bits follow these rules: (a) On the default case, where SERIALIZED_DATA_RATE is ‘00’, for a 12-bit ADC data at the output, CUSTOM_PATTERN<13:2> would be used, replacing the sampled data. These would still be controlled by LSB-first and MSB-first modes in the same way as normal ADC data are. (b) For SERIALIZED_DATA_RATE= ’01’, 10-bit output mode is selected, and bits CUSTOM_PATTERN<13:4> are used. (c) For SERIALIZED_DATA_RATE= ’10’, 16-bit output mode is selected. On this case, CUSTOM_PATTERN<13:0> are used for the first 14 most significant bits, and two zeros take the place of the LSBs. (d) For SERIALIZED_DATA_RATE= ’11’, 14-bit mode is selected, and CUSTOM_PATTERN<13:0> takes the place of the output word. 5. PATTERN_MODE equal to '100’ makes it always ‘1’, while setting it to ‘110’ makes the output always ‘0’. 6. PATTERN_MODE equal to ‘101’ makes the output of the device toggle between all zeros and all ones. On the nth sample clock, the data would be ‘000000000000’ and on the following one (nth+1) it would be ‘111111111111’. 7. PATTERN_MODE equal to ‘111’ causes all the channels to output a repeating full-scale ramp pattern. The ramp increments from zero code to full-scale code in steps of 1LSB every clock cycle. After hitting the full-scale code, it returns back to zero code and ramps again. Submit Documentation Feedback Copyright © 2008–2010, Texas Instruments Incorporated Product Folder Link(s): AFE5851 21 AFE5851 SLOS574B – SEPTEMBER 2008 – REVISED MAY 2010 www.ti.com PDN_Channel<7:0> Address: 1[9:2] Each bit controls the power down of a pair of consecutive channels (that share the same ADC). For example: PDN_Channel<0> powers down channels 1 and 2 and the corresponding LVDS pair become high impedance. DCLK and FCLK are not powered down; they will be active if terminated with 100Ω. PDN_LVDS Address: 2[10:3] PDN_LVDS<7..0> selects which LVDS pairs become inactive (zero output). The frame and clock LVDS streams get powerdown only when OUTPUT_DISABLE or GLOBAL_PDN are set. REGISTER_OFFSET_SUBSTRACTION_ENABLE Address: 3[8] Setting this bit to ‘1’ enables the subtraction of the value on the corresponding OFFSET_CHANNELi<9:2> from the ADC output. The number is specified in 2s complement format. For example, OFFSET_CHANNELi<9:2>=’1000000’ means “subtract –128”. For OFFSET_CHANNELi<9:2>=’01111111’ the effect will be to subtract 127. Hereby, both addition and subtraction can be done. Notice that the offset is applied before the digital gain (see next). In fact, digital gain is the last step and the whole data path is 2s complement through out internally. Only when DFS=’1’ (straight binary output format), the 2s complement word is translated into offset binary right at the end. REGISTER_READOUT_ENABLE Address:0[1] The device includes an option where the contents of the internal registers can be read back. This may be useful as a diagnostic to verify the serial interface communication between the external controller and the AFE. First, the <REGISTER READOUT ENABLE> bit needs to be set to ‘1’. Then the user should initiate a serial interface cycle specifying the address of the register (A7-A0) whose content has to be read. The data bits are “don’t care”. The device will output the contents (D15-D0) of the selected register on the SDOUT pin. The external controller can latch the contents at the rising edge of SCLK. To enable serial register writes, set the <REGISTER READOUT ENABLE> bit back to ‘0’. The following timing diagram shows this operation (the time specifications follow the same information provided on the table for a serial interface register write): Start sequence SEN t6 t2 End sequence t7 t1 SCLK t3 SDATA A7 t4 A6 A5 A4 A3 A1 A0 X X X X X X X X X X X X X X X X t5 SDOUT 22 A2 SDOUT TO BE LATCHED EXTERNALLY ON THE RISING EDGE D15 D14 D13 D12 D11 D10 D9 Submit Documentation Feedback D8 D7 D6 D5 D4 D3 D2 D1 D0 Copyright © 2008–2010, Texas Instruments Incorporated Product Folder Link(s): AFE5851 AFE5851 www.ti.com SLOS574B – SEPTEMBER 2008 – REVISED MAY 2010 SERIALIZED_DATA_RATE Address: 3[14:13] These two bits control the length of the data word, i.e., the number of DCLK per FCLK periods. It is possible, for instance, to output 16bit data stream, even with a 12bit ADC. In this case, the last 4 LSBs are padded with zeros. The pass from higher resolution to lower serialization is not supported though; i.e, it is not possible to select a 10bit stream with a 12bit ADC. TGC_REGISTER_WREN Address: 0[2] Set this bit to ‘1’ to access the TGC table and ‘0’ (default after reset) to access the general purpose register table. As explained before, the same address may point to one bank of registers or to the other. Nevertheless, observe that register 0 of the general purpose registers is always accessible, regardless of the value of TGC_REGISTER_WREN. The TGC table starts at address 1. VCA_LOW_NOISE_MODE Address: 7[10] Setting this bit to ‘1’ reduces the equivalent input noise of the channel to 5nV/√Hz (for a 31dB gain) at the expense of an increase in power consumption (5mW/channel). TGC CONTROL REGISTER MAP The TGC operation is described in the VGA/TGC Operation section below. This section describes the TGC control registers which can be accessed by writing '1' to TGC_REG_WREN bit. The following table describes the register map for all the registers involved in the TGC operation. ADDRESS D[15:7] D[8] D[7] D[6] 0x01...0x94 D[5] D[4] 0x95 D[2] D[1] D[0] START_ INDEX 0x96 STOP_INDEX INTERP ENABLE 0x97 0x98 D[3] REG_VALUES 0 START _GAIN HOLD_ GAIN _TIME NOT USED 0x99 0 0 0x9A 0 0 0x9B SOFT SYNC UNIFORM GAIN MODE STATIC PGA FINE_GAIN COARSE_GAIN UNIFORM_GAIN_SLOPE REG_VALUE Address: 0x01[8:0] to 0x94[8:0] Each of these 9 bit registers (148 of them) stores the time to stay at a given gain setting, during the gain ramp. The most significant bit of each register (REG_VALUE<8>) denotes either increment or decrement gain from current gain value. The other 8 bits (REG_VALUE<7:0>) denote the time (a multiple of 8 × Tclk; Tclk being the channel sampling clock, i.e., double the period of the device input clock) for the change of the gain from the CURRENT_GAIN to CURRENT_GAIN ±1dB (depending on the REG_VALUE<8>). The fastest ramp (shortest time) for this 1dB gain change is set by REG_VALUE<7:0> equal to 0x00 and it is 8 × Tclk. The slowest ramp (longest time) for this 1dB gain change is set by REG_VALUE<7:0> equal to 0xFF and it is 255 × 8 × Tclk (see VGA operation – described later). START_INDEX Address: 0x95[7:0] This 8 bit register specifies/points to the first REG_VALUE register of the TGC curve (i.e., where the curve starts) and can have values ranging from 1 to 148 (in decimal). STOP_INDEX Address: 0x96[7:0] This 8 bit register specifies/points to the last REG_VALUE register of the TGC curve (i.e., where the curve finishes) and can have values ranging from 1 to 148 (in decimal). Submit Documentation Feedback Copyright © 2008–2010, Texas Instruments Incorporated Product Folder Link(s): AFE5851 23 AFE5851 SLOS574B – SEPTEMBER 2008 – REVISED MAY 2010 www.ti.com START_GAIN Address: 0x97[5:0] This 6 bit register specifies the start gain value from –5dB to 31dB. START_GAIN = [–5 + REG_VALUE ] dB REG_VALUE GAIN 0x0 0x1 0x24 –5 dB –4 dB 31 dB STOP_GAIN (Not a programmable register, it is an internally computed value) Case 1: INTERP_ENABLE=1, STOP_GAIN = START_GAIN + (STOP_INDEX -START_INDEX) – ( 2 * Number of decrements) + 0.875dB. Case 2: INTERP_ENABLE=’0’, STOP_GAIN = START_GAIN + (STOP_INDEX-START_INDEX) – ( 2 * Number of Decrements). HOLD_GAIN_TIME Address: 0x98[7:0] This 8 bit register specifies the time for holding of the STOP_GAIN, after reaching either the STOP_GAIN value as computed earlier or the maximum/minimum gain. After this time, the TGC starts stepping down to the START_GAIN value in 1dB steps every Tclk. The STOP_GAIN value is held for the following number of clocks: HOLD_GAIN_TIME = [33 * REG_VALUE] Tclks where Tclk is the channel sampling clock. REG_VALUE 0x0 0x1 0xFF HOLD_GAIN_TIME 0 Tclks 33 Tclks 8415 Tclks INTERP_ENABLE Address: 0x97[7] This 8 bit register sets the ramp rate. When INTERP_ENABLE='1' the ramp rate is 0.125dB for every number of clocks stored in REG_VALUE: REG_VALUE 0x0 0x1 0x2 0xFF 24 SLOPE 0.125dB 0.125dB 0.125dB 0.125dB per per per per Tclk Tclk 2*Tclk 255*Tclk Submit Documentation Feedback Copyright © 2008–2010, Texas Instruments Incorporated Product Folder Link(s): AFE5851 AFE5851 www.ti.com SLOS574B – SEPTEMBER 2008 – REVISED MAY 2010 When INTERP_ENABLE='0' the ramp rate is 1dB for every 8 times the number of clocks stored in REG_VALUE: REG_VALUE 0x0 0x1 0x2 0xFF SLOPE 1dB per 1dB per 1dB per 1dB per 8 × Tclk 8 × Tclk 16 × Tclk 255× 8 × Tclk SOFT_SYNC Address 0x99[5] Setting SOFT_SYNC bit to '1' enables the TGC engine to run periodically following a given TGC curve, without the need for a high pulse signal in the SYNC pin (see more details below). UNIFORM_GAIN_MODE Address 0x99[4] Setting this bit to ‘0’ (default) directs the TGC engine to follow an arbitrary gain versus time curve. If this bit to ‘1’ the gain is ramped up with a slope set by the UNIFORM_GAIN_SLOPE register. (See more details below) UNIFORM_GAIN_SLOPE Address 0x9B[7:0] See Uniform Gain Increment Mode section below. STATIC_PGA Address 0x99[3] Setting this bit to ‘1’ disables the TGC engine. COARSE_GAIN and FINE_GAIN will control the gain value, which will be independent of time. COARSE_GAIN Address 0x9A[5:0] This 6 bit register specifies the coarse gain from –5 to 31dB, in 1dB steps. Observe that only values from 0x00 to 0x24, both included, are valid. Setting a value bigger than 0x24 on the COARSE_GAIN register is the same as setting 0x24. COARSE_GAIN = [–5 + REG_VALUE ] dB REG_VALUE 0x0 0x1 0x24 GAIN –5dB –4dB 31dB FINE_GAIN Address 0x99[2:0] This 3 bit register specifies the fine gain in steps of 0.125dB resolution, from 0dB to 0.875dB. FINE_GAIN = [0.125 × REG_VALUE ] dB REG_VALUE 0x0 0x1 0x7 GAIN 0dB 0.125dB 0.875dB VGA/TGC OPERATION The gain variation of the variable gain amplifier (VGA) versus time is called TGC function and on the AFE5851 is controlled digitally. The gain is implemented by a switched network where the switches controlling the gain are synchronized with the ADC sampling instant to minimize glitches on the output data. The gain setting depends on the mode of operation selected by the user. There are 3 possible modes of operation: non-uniform gain, uniform gain, and static mode. The following sections describe each in detail. Submit Documentation Feedback Copyright © 2008–2010, Texas Instruments Incorporated Product Folder Link(s): AFE5851 25 AFE5851 SLOS574B – SEPTEMBER 2008 – REVISED MAY 2010 www.ti.com Sync Period GAIN Profile SYNC Signal Input to AFE5851 External System Signal Wait time at start gain, tw Ramp up time from start gain to stop gain, tru Hold time at Wait time stop gain, at start gain th Ramp down from stop gain to start gain, trd Sync Period = tru + th + trd + tw Figure 34. SYNC Period Non-Uniform Gain Increment Mode In the non-uniform gain increment mode, the user sets an arbitrary shape for the gain versus time curve. For a given time/sampling instant, the digital gain setting is obtained from an internal memory of 148 positions/registers (named REG_VALUEs), each 9 bits wide, loaded by the user through the serial port (see Serial Interface section). Addresses 1 to 148 can be used to access these registers, while TGC_REGISTER_WREN='1'. As explained above, the most significant bit of each register (REG_VALUE<8>) denotes either increment or decrement gain from current gain value. The other 8 bits (REG_VALUE<7:0>) denote the time (a multiple of 8*Tclk, being Tclk the sampling clock) for the change of the gain from the CURRENT_GAIN to CURRENT_GAIN ±1dB (depending on the REG_VALUE<8>). The fastest ramp (shortest time) for this 1dB gain change is set by REG_VALUE<7:0> equal to 0x00 and it is 8 × Tclk. The slowest ramp (longest time) for this 1dB gain change is set by REG_VALUE<7:0> equal to 0xFF and it is 255 × 8 × Tclk. INTERP_ENABLE sets the way the gain is increased/decreased. By default the gain ramp is implemented in steps of 1dB (INTERP_ENABLE equal to 0). If INTERP_ENABLE is equal to 1, the actual 1dB gain step is implemented in 8 steps of 0.125dB. The 148 REG_VALUE registers can be used to store either a single curve or multiple TGC curves. The START_INDEX register points to the REG_VALUE register where the TGC curve starts and the STOP_INDEX register points to the REG_VALUE register where the TGC curve stops. Using the START_INDEX and STOP_INDEX registers the desired TGC curves can be chosen. 26 Submit Documentation Feedback Copyright © 2008–2010, Texas Instruments Incorporated Product Folder Link(s): AFE5851 AFE5851 www.ti.com SLOS574B – SEPTEMBER 2008 – REVISED MAY 2010 As shown in Figure 34, a pulse high signal on the SYNC pin will set the starting gain value of the TGC curve to the START_GAIN register value, and it will initiate the progression through the different REG_VALUEs, starting at START_INDEX. Observe that there is no option to delay the start of gain stepping after the SYNC pulse is received. Then, the progression continues until either the STOP_INDEX is reached or maximum/minimum gain is exceeded. After that, the last valid value of gain is held for an extra given number of clocks set by the register HOLD_GAIN_TIME. After the elapsing of clocks mentioned by the HOLD_GAIN_TIME register, the TGC starts to step down (or up) to the START_GAIN in steps of 1dB every Tclk (channel sampling clock) in preparation for the next TGC profile. The TGC will start updating/following the REG_VALUEs again after a new high pulse on the SYNC pin is given. The SYNC signal is latched by the rising edge of the channel sampling clock. In other words, the gain increments at the rising edge of the channel sampling clock. Setup time with rising edge is 7ns, and hold time 4ns. SOFT_SYNC The TGC can run periodically following a given TGC curve but without the need for a high pulse signal in the SYNC pin. This is done by setting SOFT_SYNC bit to '1'. Once this bit is set, the sequence of events is the same as with the hardwired SYNC pulse. The TGC curve updates from START_INDEX to STOP_INDEX. After reaching STOP_INDEX or the maximum/minimum gain, the STOP_GAIN value is held for HOLD_VALUE_TIME and then the gain ramps up or down to START_GAIN. After this the TGC update starts again automatically and repeats all these steps periodically till the SOFT_SYNC bit becomes zero. The SYNC process through register write occurs at the serial clock edge where the register is written. If serial clock and sample clock (channel sampling clock) are synchronous then the described relation in the hardwired SYNC section will hold and the SYNC bit is latched by the rising edge of the channel sampling clock, respecting a setup time with rising edge of 7ns and hold time of 4ns. If sample clock and serial clock are not synchronous then this relationship does not apply and a clock uncertainty of ±1 sample will apply in respect to the nearest sample clock rising edge. Example 1: In the following example of non-uniform gain mode, all the 148 registers are loaded. Nevertheless, the start address for the TGC is set in START_INDEX to 2 and the stop address (STOP_INDEX) to 7. The START_GAIN is set to 6 and HOLD_GAIN_TIME is 4. With a high pulse on the SYNC pin the gain starts from 1dB (START_GAIN=0x06). 1dB to 2dB ramp is done in 120Tclks, using eight 0.125dB steps (as INTERP_ENABLE is set to 1), each 15Tclks long. The ramp from 2dB to 3dB is done in 64Tclks, also in 0.125dB steps. The ramp from 3dB to 4dB is done in 40 Tclks. Decrement from 4dB to 3dB in 64Tclks. Gain increment from 3dB to 4dB in 56 Tclks and from 4dB to 4.875dB in 80 Tclks. Observe that in the case where INTERP_ENABLE=1, STOP_GAIN = START_GAIN + (STOP_INDEX -START_INDEX) – ( 2 × Number of decrements) + 0.875dB. In the case where INTERP_ENABLE=’0’, STOP_GAIN = START_GAIN + (STOP_INDEX-START_INDEX) – ( 2 × Number of Decrements). This is due to the fact that the interpolation engine keeps the gain increasing or decreasing when INTERP_ENABLE=1, while the gain is frozen when INTERP_ENABLE=0. TGC REG INDEX REG_VALUE[8:0] Number of Tclks Direction of Gain Change 1 0x004 4 × 8 = 32 Increment 2 0x00F 15 × 8 = 120 Increment 3 0x008 8 × 8 = 64 Increment 4 0x005 5 × 8 40 Increment 5 0x108 8 × 8 = 64 Decrement 6 0x007 7 × 8 = 56 Increment Increment 7 0x00A 10 × 8 = 80 ... ... ... ... 147 0x00F 15 × 8 = 120 Increment 148 0x00F 15 × 8 = 120 Increment Submit Documentation Feedback Copyright © 2008–2010, Texas Instruments Incorporated Product Folder Link(s): AFE5851 27 AFE5851 SLOS574B – SEPTEMBER 2008 – REVISED MAY 2010 www.ti.com NAME VALUE START_INDEX 0x02 STOP_INDEX 0x07 START_GAIN 0x06 HOLD_GAIN_TIME 0x04 INTERP_ENABLE 1 UNIFORM_GAIN_MODE 0 Uniform Gain Increment Mode By setting UNIFORM_GAIN_MODE to '1', the TGC engine can also be configured for a uniform increment gain ramp mode where the gain is ramped up from the START_GAIN value to the STOP_GAIN with a slope set by the UNIFORM_GAIN_SLOPE register. Note: STOP_GAIN is not a programmable register, but just an internally computed value from START_GAIN, UNIFORM_GAIN_SLOPE, START_INDEX and STOP_INDEX. If INTERP_ENABLE=1, UNIFORM_GAIN_SLOPE sets the number of Tclk (channel sampling clock) at a given gain before incrementing or decrementing 0.125dB. If INTERP_ENABLE=0, this register sets the number of 8*Tclk (eight sampling periods) at a given gain before incrementing or decrementing 1dB. Observe that in both cases the time it takes to step by 1dB is the same. In INTERP_ENABLE=0 the gain is stationary at the same setting for the given time, while in the other case the gain increments in fine gain steps of 0.125dB to cover that 1dB step When INTERP_ENABLE is zero, the STOP_GAIN is computed as START_GAIN + (STOP_INDEX-START_INDEX). Nevertheless, when INTERP_ENABLE = '1', the STOP_GAIN is equal to START_GAIN + (STOP_INDEX - START_INDEX) + 0.875dB. This is basically due to the fact that the interpolation engine keeps the gain increasing on the second case, while, as explained above, is frozen on the first case. Observe that START_INDEX and STOP_INDEX are not used in this case as pointers to the REG_VALUEs table. Instead, only the difference between the two is important to compute STOP_GAIN. As such, START_INDEX can be set to zero and STOP_INDEX will store STOP_GAIN – START_GAIN. Observe that only positive slope ramps are possible. Example 1: setting START_GAIN=0x2 (–3dB), START_INDEX=0x00, STOP_INDEX=0x06, INTERP_ENABLE=0 and UNIFORM_GAIN_SLOPE=0x8, will set the gain at –3dB for 8 × 8 × Tclk, then to –2dB for another 64 Tclk, and so on, through –1, 0, 1, 2 and 3. After spending 64 × Tclk in 3dB, the gain will stay at that gain setting for HOLD_GAIN_TIME and start stepping down back to START_GAIN, with 1dB per Tclk. Example 2: for the same settings, START_GAIN=0x2 (–3dB), START_INDEX=0x00, STOP_INDEX=0x06, and UNIFORM_GAIN_SLOPE=0x8, if we set INTERP_ENABLE=1, the gain will start at –3dB for 8Tclk, then –2.875dB for another 8Tclk, then –2.750dB and so on, till 3dB. At this point, while in example 1, with INTERP_ENABLE=0 the gain would be frozen for another 64 Tclk, in this example, the gain will continue to increase with 0.125dB steps every 8Tclk till 3.875dB is reached. There will stay for another 8Tclk before starting to wait for HOLD_GAIN_TIME and start stepping down. Example 3: for START_GAIN=0x2(–3dB) , START_INDEX=0x00, STOP_INDEX=0x00, INTERP_ENABLE=1 and UNIFORM_GAIN_SLOPE=0x1, the gain will step through –3dB, –2.875, –2.75, –2.625, –2.5, –2.375, –2.25 and –2.125, staying at each of these 8 values 1 clock cycle (8 total). Then it will wait for HOLD_GAIN_TIME in –2.125dB and then it will start stepping down back to –3dB. Example 4: same settings as example 3, but with INTERP_ENABLE=0, would simply set the VGA gain to –3dB for 8 clock cycles and then the logic would wait for HOLD_GAIN_TIME. Static PGA Mode The 3rd mode of operation is actually a mode where the TGC engine is disabled by writing '1' into the STATIC_PGA bit. This enables the use of a fixed gain mode where the gain is obtained by the sum of a coarse and a fine gain. Coarse gain can be set from –5 to 31dB, in 1dB steps, by the register COARSE_GAIN (6 bit word from 0x00 to 0x24). Setting a value bigger than 0x24 on the COARSE_GAIN register is the same as setting 0x24. The fine gain can be set in steps of 0.125dB resolution, from 0dB to 0.875dB by the FINE_GAIN register (3 bit word with range from 0x00 to 0x07). Observe that the maximum gain, when both registers are set to their maximum gains, is actually 31.875dB. 28 Submit Documentation Feedback Copyright © 2008–2010, Texas Instruments Incorporated Product Folder Link(s): AFE5851 AFE5851 www.ti.com SLOS574B – SEPTEMBER 2008 – REVISED MAY 2010 ANTI ALIAS FILTER (AAF) The AFE5851 integrates a selectable 3 order low pass filter for each of the 16 channels. The cutoff frequency can be set for all the channels simultaneously through the serial interface (see FILTER_BW register, in the General Purpose Register table) between 3 possible settings: 7.5, 10 and 14MHz. Figure 19 shows the frequency response for each of these settings. The filter characteristics are set by passive components which are subject to variations over process and temperature. A typical variation of ±5% on the frequency characteristics is expected. CLAMPING CIRCUIT AND OVERLOAD RECOVERY The AFE5851 is designed in particular for ultrasound applications where the front-end device is required to recover very quickly from an overload condition. Such overload can either be the result of a transmit pulse feed-through or a strong echo, which can cause overload of the VGA and ADC. Enabled by default, the AFE5851 includes a clamping circuit to further optimize the overload recovery behavior of the complete channel (see Figure 31). The circuit can be disabled by writing a '1' in the bit 14 of the address 70 (decimal) of the General Purpose Register Map. The clamp is set to limit the signal at 3dB above the full scale of the ADC (2Vpp). CLOCK INPUTS The 16 channels on the device operate from a single clock input. To ensure that the aperture delay and jitter are the same for all channels, the AFE5851 uses a clock tree network to generate individual sampling clocks to each channel. The clock channels for all the channels are matched from the source point to the sampling circuit of each of the eight internal ADCs. The variation on this delay is described in the Aperture Delay parameter of the Output Interface Timing. Its variation over time is described in the Aperture Jitter number of the same table. Observe that the rising edges of the input clock are used to sample the even channels in one input clock period and the odd channels in the next. Using an input clock double the speed of the channel sampling clock ensures that the sampling instant between even and odd channels is exactly an input clock period apart and does not depend on its duty cycle.. The AFE5851 clock input can be driven differentially (sinewave, LVPECL or LVDS) or single-ended (LVCMOS). The clock input of the device has an internal buffer/clock amplifier (see Figure 35) which is enabled or disabled automatically depending on the type of clock provided (autodetect feature). When enabled, the device will consume 6mW more power from the AVDD18 supply rail, but it will also accept differential or single ended inputs of smaller swing. AVDD18 VCM VCM 5 kW 5 kW CLKP CLKM Figure 35. Internal Clock Buffer for Differential Clock Mode Submit Documentation Feedback Copyright © 2008–2010, Texas Instruments Incorporated Product Folder Link(s): AFE5851 29 AFE5851 SLOS574B – SEPTEMBER 2008 – REVISED MAY 2010 www.ti.com If the preferred clocking scheme for the device is single-ended, CLKINM pin should be connected to ground, i.e., shorted directly to AVSS (see Figure 37). In this case, the autodetect feature will shut down the internal clock buffer and the device will go into single-ended clock input automatically. The user should connect the single-ended clock source directly (no decoupling) to CLKINP pin, which would be the only device clock input. In that case, it is recommended the use of low jitter square signals (LVCMOS levels, 1.8V amplitude) to drive the ADC (see SLYT075 for further details on the theory). For single ended sinusoidal clocks or for differential clocks (differential sinewave, LVPECL, LVDS…), the clock amplifier should be enabled. For that, the connection scheme of Figure 36 should be used. The common-mode voltage of the clock source should match one of the clock inputs of the AFE5851 (VCM) which is set internally using 5kΩ resistors, as shown in Figure 35. The easiest way to ensure this is to AC couple the inputs as shown in Figure 36. The same scheme applies to the case where the clock is single ended but its amplitude is small or its edges are not sharp (for instance, with a sinusoidal single-ended clock). In this case, the input clock signal can be connected with a capacitor to CLKINP (as in Figure 36) and the CLKINM should be connected to ground also through a capacitor, i.e., AC coupled to AVSS. 0.1 mF CLKP Differential Sine-Wave or PECL or LVDS Clock Input 0.1 mF CLKM AFE5851 AFE5851 Figure 36. Differential Clock Driving Circuit If a transformer is used with the secondary floating (for instance, to pass from single-ended to differential) , it can then obviously be connected directly to the clock inputs, without the need of the 100nF series capacitors. CMOS Clock Input CLKP CLKM AFE5851 AFE5851 Figure 37. Single-Ended Clock Driving Circuit 30 Submit Documentation Feedback Copyright © 2008–2010, Texas Instruments Incorporated Product Folder Link(s): AFE5851 AFE5851 www.ti.com SLOS574B – SEPTEMBER 2008 – REVISED MAY 2010 Finally, on the differential clock configurations, Figure 38 shows the use of the CDCM7005 to generate the AFE5851 clock signals. VCC Reference Clock REF_IN VCC Y0 CLKP Y0B CLKM CDCM7005 AFE5851 OUTP VCXO_INP OUTM VCXO_INM CTRL CP_OUT VCXO Figure 38. PECL Clock Drive Using CDCM7005 DIGITAL OUTPUTS The conversion results from all 8 ADCs are serialized and output using one LVDS data pair per ADC, at 12 times the device input clock rate. Besides that, two more LVDS pairs are used to facilitate the interface to the circuit reading the ADC output. For one side, a reference frame LVDS signal running at the channel rate (half the input clock rate) indicates the beginning and end of the sample word. On top of that, the device outputs a reference clock running at 6 times the input clock rate, with rise and fall times aligned with the individual bits. See the Output Interface Timing section for a description of the timing diagram as well as details on the timing margins. Figure 39 represents the device LVDS output circuit. Observe that for an LVDS output high (OUTP=1.375V, OUTM=1.025V) the "high" switches would be closed and the “low” switches would be open. For LVDS output low (OUTP=1.025V, OUTM=1.375V) the “low” switches would be closed and the “high” left open. As the “high” and “low” switches have a nominal RON of 50Ω ±10%, notice that the output impedance will be nominally 100Ω in any of those two configurations (“high” or “low” switches closed). Submit Documentation Feedback Copyright © 2008–2010, Texas Instruments Incorporated Product Folder Link(s): AFE5851 31 AFE5851 +0.35 V Low www.ti.com High SLOS574B – SEPTEMBER 2008 – REVISED MAY 2010 OUTP -0.35 V High 1.2 V Low External 100 W Load ROUT OUTM Switch impedance is Nominally 50 W ( ±10%) Figure 39. LVDS Output Circuit EXTERNAL/INTERNAL REFERENCE See EXTERNAL_REFERENCE register description in the General Purpose Register Description Section. POWER SUPPLIES The use of low noise power supplies with adequate decoupling is recommended, being the linear supplies the first choice vs switched ones, which tend to generate more noise components that can be coupled to the AFE5851. There is no need of any type of power-up sequencing, although a positive pulse must be applied to the Reset pin once the power supplies are considered stable (see Serial Interface Section) There are several types of powerdown modes. On the standby mode all circuits but the reference generator are powered-down. This enables for a fast recovery from power down to full operation. On the full power down mode, all the blocks are powered down (except some digital circuits). The power savings are bigger but the power-up will also be slower (see specification tables for more details). The device includes also the possibility of powering down pairs of channels (corresponding to the same ADC) through the use of PDN_Channel<7:0> and powering down the LVDS outputs by using PDN_LVDS. Finally, notice that the metallic heat sink under the package is also connected to analog ground. LAYOUT INFORMATION The evaluation board represents a good guideline of how to layout the board to obtain the maximum performance out of the AFE5851. General design rules as the use of multilayer boards, single ground plane for both, analog and digital ADC ground connections, and local decoupling ceramic chip capacitors should be applied. The input traces should be isolated from any external source of interference or noise, including the digital outputs as well as the clock traces. Clock should also be isolated from other signals although the low frequencies of the input signal relaxes the jitter requirements. In order to maintain proper LVDS timing, all LVDS traces should follow a controlled impedance design (for example, 100Ω differential). In addition, all LVDS trace lengths should be equal and symmetrical. It is recommended to keep trace length variations less than 150mil (0.150in or 3.81mm). It is necessary to solder the exposed pad at the bottom of the package to a ground plane for best thermal performance. For detailed information, see application notes QFN Layout Guidelines (SLOA122A) and QFN/SON PCB Attachment (SLUA271A). 32 Submit Documentation Feedback Copyright © 2008–2010, Texas Instruments Incorporated Product Folder Link(s): AFE5851 AFE5851 www.ti.com SLOS574B – SEPTEMBER 2008 – REVISED MAY 2010 DEFINITION OF SPECIFICATIONS Analog Bandwidth – The analog input frequency at which the power of the fundamental is reduced by 3 dB with respect to the low frequency value. Aperture Delay –The delay in time between the rising or the falling edge of the input sampling clock (depending on the channel) and the actual time at which the sampling occurs. This delay will be different across channels. The maximum variation is specified as aperture delay variation (channel-channel). Aperture Uncertainty (Jitter) – The sample-to-sample variation in aperture delay. Clock Pulse Width/Duty Cycle – The duty cycle of a clock signal is the ratio of the time the clock signal remains at a logic high (clock pulse width) to the period of the clock signal. Duty cycle is typically expressed as a percentage. A perfect differential sine-wave clock results in a 50% duty cycle. Maximum Conversion Rate – The maximum sampling rate at which certified operation is given. All parametric testing is performed at this sampling rate unless otherwise noted. Minimum Conversion Rate – The minimum sampling rate at which the ADC functions. Differential Nonlinearity (DNL) – An ideal ADC exhibits code transitions at analog input values spaced exactly 1 LSB apart. The DNL is the deviation of any single step from this ideal value, measured in units of LSBs. Integral Nonlinearity (INL) – The INL is the deviation of the ADC's transfer function from a best fit line determined by a least squares curve fit of that transfer function, measured in units of LSBs. Gain Error – The difference between the actual gain of a channel & its ideal (theoretical) gain, i.e., the error in the absolute gain of the channel. Gain Matching – The gain difference between two channels with same theoretical gain setting. For perfect matching, the difference should be zero. On the context of this device, the gain matching is obtained in two different ways: 1. The values on the specification table represent the expected gain matching between any two channels on the system. The gain is measured on every channel of every device, for a given gain setting, at any temperature. The difference between the maximum recorded gain and the minimum recorded gain represents the gain matching at that given gain setting. The same is done for every gain setting and the maximum difference for any gain setting is presented on the table. 2. The gain matching histogram represents the channel to channel matching inside the same device, i.e., the maximum expected gain difference between any two channels of the same device, or in other words, the peak-to-peak variation of absolute gains across all channels in the device. At a given gain setting for all the channels of a given device (at one temperature assumed common to the whole device), the difference between the channel with maximum gain and the channel with minimum gain represents one count. The same thing is done for all the devices and for 3 temperatures (–40C, 25C and 85C). Every measurement of a device at one given temperature represents one count. Offset Error – The offset error is the difference, given in mV, between the ADC's actual average idle channel output code and the ideal average idle channel output code. Temperature Drift – The temperature drift coefficient (with respect to gain error and offset error) specifies the change per degree Celsius of the parameter from TMIN to TMAX. It is calculated by dividing the maximum deviation of the parameter across the TMIN to TMAX range by the difference TMAX–TMIN. Signal-to-Noise Ratio – SNR is the ratio of the power of the fundamental (PS) to the noise floor power (PN), excluding the power at DC and the first nine harmonics. P SNR + 10Log10 S PN (1) SNR is either given in units of dBc (dB to carrier) when the absolute power of the fundamental is used as the reference, or dBFS (dB to full scale) when the power of the fundamental is extrapolated to the converter’s full-scale range. Signal-to-Noise and Distortion (SINAD) – SINAD is the ratio of the power of the fundamental (PS) to the power of all the other spectral components including noise (PN) and distortion (PD), but excluding dc. Submit Documentation Feedback Copyright © 2008–2010, Texas Instruments Incorporated Product Folder Link(s): AFE5851 33 AFE5851 SLOS574B – SEPTEMBER 2008 – REVISED MAY 2010 SINAD = 10 log 10 www.ti.com PS PN + PD (2) SINAD is either given in units of dBc (dB to carrier) when the absolute power of the fundamental is used as the reference, or dBFS (dB to full scale) when the power of the fundamental is extrapolated to the converter's full-scale range. Effective Number of Bits (ENOB) – The ENOB is a measure of a converter’s performance as compared to the theoretical limit based on quantization noise. ENOB + SINAD * 1.76 6.02 (3) Spurious Free Dynamic Range (SFDR) – SFDR is the ratio of the power of the fundamental (PS) to the highest FFT bin, harmonic or not, excluding DC. SFDR is typically given in units of dBc (dB to carrier). Second Harmonic Distortion (HD2) – HD2 is the ratio of the power of the fundamental (PS) to the second harmonic, typically given in units of dBc (dB to carrier). Third Harmonic Distortion (HD3) –HD3 is the ratio of the power of the fundamental (PS) to the third harmonic, typically given in units of dBc (dB to carrier). Total Harmonic Distortion (THD) – THD is the ratio of the power of the fundamental (PS) to the power of the first nine harmonics (PD). THD = 10 log 10 PS PD (4) THD is typically given in units of dBc (dB to carrier). AC Power Supply Rejection Ratio (AC PSRR) – A measure of the device immunity to variations in its supply voltage. In this datasheet, if ΔVSUP represents the change in supply voltage and ΔVOUT is the resultant change of the ADC output code (referred to the input), then: æ DVout ö PSRR = 20 log ç ÷ è DVsup ø 34 (5) Submit Documentation Feedback Copyright © 2008–2010, Texas Instruments Incorporated Product Folder Link(s): AFE5851 AFE5851 www.ti.com SLOS574B – SEPTEMBER 2008 – REVISED MAY 2010 REVISION HISTORY NOTE: Page numbers of current version may differ from previou versions. Changes from Original (September 2008) to Revision A • Page Changed document status from Product Preview to Production Data ................................................................................. 1 Changes from Revision A (March 2009) to Revision B Page • Deleted Registers 3[7:0] INVERT CHANNEL and 4[4] MSB_FIRST from General Purpose Register Map ...................... 18 • Deleted description for Registers 3[7:0] INVERT_CHANNEL; and, 4[4] MSB_FIRST ....................................................... 21 Submit Documentation Feedback Copyright © 2008–2010, Texas Instruments Incorporated Product Folder Link(s): AFE5851 35 PACKAGE MATERIALS INFORMATION www.ti.com 5-Feb-2010 TAPE AND REEL INFORMATION *All dimensions are nominal Device Package Package Pins Type Drawing SPQ Reel Reel A0 Diameter Width (mm) (mm) W1 (mm) B0 (mm) K0 (mm) P1 (mm) W Pin1 (mm) Quadrant AFE5851IRGCR VQFN RGC 64 2000 330.0 16.4 9.3 9.3 1.5 12.0 16.0 Q2 AFE5851IRGCT VQFN RGC 64 250 330.0 16.4 9.3 9.3 1.5 12.0 16.0 Q2 Pack Materials-Page 1 PACKAGE MATERIALS INFORMATION www.ti.com 5-Feb-2010 *All dimensions are nominal Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm) AFE5851IRGCR VQFN RGC 64 2000 333.2 345.9 28.6 AFE5851IRGCT VQFN RGC 64 250 333.2 345.9 28.6 Pack Materials-Page 2 IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, modifications, enhancements, improvements, and other changes to its products and services at any time and to discontinue any product or service without notice. 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