Data Sheet CDK1308 Ultra Low Power, 20/40/65/80MSPS, 10-bit Analog-to-Digital Converters (ADCs) n 10-bit resolution n 20/40/65/80MSPS max sampling rate n The CDK1308 is a high performance ultra low power analog-to-digital converter (ADC). The ADC employs internal reference circuitry, a CMOS control interface and CMOS output data, and is based on a proprietary structure. Digital error correction is employed to ensure no missing codes in the complete full scale range. Ultra-Low Power Dissipation: 15/25/38/46mW n 61.6dB SNR at 80MSPS and 8MHz FIN n Internal reference circuitry n 1.8V core supply voltage n 1.7 – 3.6V I/O supply voltage n Parallel CMOS output n 40-pin QFN package n Pin compatible with CDK1307 Two idle modes with fast startup times exist. The entire chip can either be put in Standby Mode or Power Down mode. The two modes are optimized to allow the user to select the mode resulting in the smallest possible energy consumption during idle mode and startup. The CDK1308 has a highly linear THA optimized for frequencies up to Nyquist. The differential clock interface is optimized for low jitter clock sources and supports LVDS, LVPECL, sine wave, and CMOS clock inputs. APPLICATIONS n Medical Imaging n Portable Test Equipment n Digital Oscilloscopes n IF Communication n Video Conferencing n Video Distribution Functional Block Diagram Rev 1B 10 Ordering Information Part Number Speed Package Pb-Free RoHS Compliant Operating Temperature Range Packaging Method CDK1308AILP40 20MSPS QFN-40 Yes Yes -40°C to +85°C Tray CDK1308BILP40 40MSPS QFN-40 Yes Yes -40°C to +85°C Tray CDK1308CILP40 65MSPS QFN-40 Yes Yes -40°C to +85°C Tray CDK1308DILP40 80MSPS QFN-40 Yes Yes -40°C to +85°C Tray Moisture sensitivity level for all parts is MSL-2A. Exar Corporation 48720 Kato Road, Fremont CA 94538, USA CDK1308 Ultra Low Power, 20/40/65/80MSPS, 10-bit ADCs General Description FEATURES www.exar.com Tel. +1 510 668-7000 - Fax. +1 510 668-7001 Data Sheet Pin Configuration SLP_N CM_EXTBC_0 CM_EXTBC_1 OVDD OVDD D_9 D_8 D_7 D_6 D_5 39 38 37 36 35 34 33 32 31 DVDD 1 30 D_4 CM_EXT 2 29 D_3 AVDD 3 28 D_2 AVDD 4 27 CLK_EXT IP 5 26 OVDD IN 6 25 OVDD AVDD 7 24 ORNG DVDDCLK 8 23 D_1 CLKP 9 22 D_0 CLKN 10 21 NC CDK1308 11 12 13 14 15 16 17 18 19 20 DVDD CLK_EXT_EN DFRMT PD_N OE_N DVDD OVDD OVDD NC NC QFN-40 CDK1308 Ultra Low Power, 20/40/65/80MSPS, 10-bit ADCs 40 QFN-40 Pin Assignments Pin No. Pin Name Description 0 VSS 1, 11, 16 DVDD 2 CM_EXT 3, 4, 7 AVDD Analog supply voltage, 1.8V 5, 6 IP, IN Analog input (non-inverting, inverting) 8 DVDDCLK 9 CLKP Clock input, non-inverting (format: LVDS, LVPECL, CMOS/TTL, Sine Wave) 10 CLKN Clock input, inverting. For CMOS input on CLKP, connect CLKN to ground 12 CLK_EXT_EN CLK_EXT signal enabled when low (zero). Tristate when high. 13 DFRMT Data format selection. 0: Offset Binary, 1: Two's Complement 14 PD_N Full chip Power Down mode when Low. All digital outputs reset to zero. After chip power up always apply Power Down mode before using Active Mode to reset chip. 15 OE_N Output Enable. Tristate when high 17, 18, 25, 26, 36, 37 OVDD I/O ring post-driver supply voltage. Voltage range 1.7 to 3.6V 19 NC 20 NC 21 NC 22 D_0 Ground connection for all power domains. Exposed pad Digital and I/O-ring pre driver supply voltage, 1.8V Common Mode voltage output Rev 1B Clock circuitry supply voltage, 1.8V Output Data (LSB) ©2009-2013 Exar Corporation 2/14 Rev 1B Data Sheet Pin Assignments (Continued) Pin No. Description 23 D_1 Output Data 24 ORNG Out of Range flag. High when input signal is out of range 27 CLK_EXT Output clock signal for data synchronization. CMOS levels 28 D_2 Output Data 29 D_3 Output Data 30 D_4 Output Data 31 D_5 Output Data 32 D_6 Output Data 33 D_7 Output Data 34 D_8 Output Data 35 D_9 Output Data (MSB) 38, 39 CM_EXTBC_1, CM_EXTBC_0 40 SLP_N CDK1308 Ultra Low Power, 20/40/65/80MSPS, 10-bit ADCs Pin Name Bias control bits for the buffer driving pin CM_EXT 00: OFF 01: 50μA 10: 500μA 11: 1mA Sleep Mode when low Rev 1B ©2009-2013 Exar Corporation 3/14 Rev 1B Data Sheet Absolute Maximum Ratings The safety of the device is not guaranteed when it is operated above the “Absolute Maximum Ratings”. The device should not be operated at these “absolute” limits. Adhere to the “Recommended Operating Conditions” for proper device function. The information contained in the Electrical Characteristics tables and Typical Performance plots reflect the operating conditions noted on the tables and plots. Min Max Unit AVDD DVDD AVSS, DVSSCK, DVSS, OVSS OVDD CLKP, CLKN Analog inputs and outpts (IPx, INx) Digital inputs Digital outputs -0.3 -0.3 -0.3 -0.3 -0.3 -0.3 -0.3 -0.3 +2.3 +2.3 +0.3 +3.9 +3.9 +2.3 +3.9 +3.9 V V V V V V V V CDK1308 Ultra Low Power, 20/40/65/80MSPS, 10-bit ADCs Parameter Reliability Information Parameter Min Storage Temperature Range Lead Temperature (Soldering, 10s) -60 Typ Max Unit +150 °C J-STD-20 ESD Protection Product QFN-40 Human Body Model (HBM) 2kV Recommended Operating Conditions Parameter Min Operating Temperature Range -40 Typ Max Unit +85 °C Rev 1B ©2009-2013 Exar Corporation 4/14 Rev 1B Data Sheet Electrical Characteristics (AVDD = 1.8V, DVDD = 1.8V, DVDDCLK = 1.8V, OVDD = 2.5V, 20/40/65/80MSPS clock, 50% clock duty cycle, -1dBFS 8MHz input signal, unless otherwise noted) Symbol Parameter Conditions Min Typ Max Units DC Accuracy Guaranteed Offset Error Midscale offset Gain Error Full scale range deviation from typical 1 -6 LSB 6 %FS DNL Differential Non-Linearity ±0.15 LSB INL Integral Non-Linearity ±0.2 LSB VCMO Common Mode Voltage Output VAVDD/2 V Analog Input VCMI Input Common Mode Analog input common mode voltage VCM -0.1 VCM +0.2 V VFSR Full Scale Range Differential input voltage range 2.0 Input Capacitance Differential input capacitance 2.0 Bandwidth Input bandwidth, full power 500 AVDD, DVDD Core Supply Voltage Supply voltage to all 1.8V domain pins. See Pin Configuration and Description 1.7 1.8 2.0 V 2.5 3.6 V I/O Supply Voltage Output driver supply voltage (OVDD). Must be higher than or equal to Core Supply Voltage (VOVDD ≥ VDVDD) 1.7 OVDD Vpp pF MHz Power Supply CDK1308 Ultra Low Power, 20/40/65/80MSPS, 10-bit ADCs No Missing Codes Rev 1B ©2009-2013 Exar Corporation 5/14 Rev 1B Data Sheet Electrical Characteristics - CDK1308A (AVDD = 1.8V, DVDD = 1.8V, DVDDCLK = 1.8V, OVDD = 2.5V, 20MSPS clock, 50% clock duty cycle, -1dBFS 8MHz input signal, unless otherwise noted) Symbol Parameter Conditions Min Typ Max Units 61.7 dBFS 60 61.6 dBFS FIN ≃ FS/2 61.6 dBFS FIN = 20MHz 61.6 dBFS FIN = 2MHz 61.7 dBFS Performance SNR SINAD Signal to Noise Ratio Signal to Noise and Distortion Ratio FIN = 8MHz FIN = 8MHz 61.6 dBFS FIN ≃ FS/2 60 60.5 dBFS FIN = 20MHz 61.6 dBFS 80 dBc 81 dBc 70 dBc FIN = 20MHz 80 dBc FIN = 2MHz -90 dBc -90 dBc FIN ≃ FS/2 -90 dBc FIN = 20MHz -90 dBc FIN = 2MHz -80 dBc -81 dBc FIN ≃ FS/2 -70 dBc FIN = 20MHz -80 dBc FIN = 2MHz 10.0 bits FIN = 2MHz SFDR HD2 HD3 ENOB Spurious Free Dynamic Range Second order Harmonic Distortion Third order Harmonic Distortion Effective number of Bits FIN = 8MHz 70 FIN ≃ FS/2 FIN = 8MHz -80 FIN = 8MHz -70 FIN = 8MHz 9.7 bits 9.8 bits FIN = 20MHz 9.9 bits 5.7 mA Digital core supply 1.0 mA 2.5V output driver supply, sine wave input, FIN = 1MHz, CLK_EXT enabled 1.7 mA 2.5V output driver supply, sine wave input, FIN = 1MHz, CLK_EXT disabled 1.2 mA Power Supply AIDD Analog Supply Current DIDD Digital Supply Current OIDD Output Driver Supply Analog Power Dissipation 10.3 mW Digital Power Dissipation OVDD = 2.5V, 5pF load on output bits, FIN = 1MHz, CLK_EXT disabled 4.8 mW Total Power Dissipation OVDD = 2.5V, 5pF load on output bits, FIN = 1MHz, CLK_EXT disabled 15.1 mW Power Down Dissipation Sleep Mode Power Dissipation, Sleep mode 9.9 µW 7.7 mW Clock Inputs Max. Conversion Rate 20 Min. Conversion Rate ©2009-2013 Exar Corporation MSPS 15 6/14 MSPS Rev 1B Rev 1B 9.9 FIN ≃ FS/2 CDK1308 Ultra Low Power, 20/40/65/80MSPS, 10-bit ADCs FIN = 2MHz Data Sheet Electrical Characteristics - CDK1308B (AVDD = 1.8V, DVDD = 1.8V, DVDDCLK = 1.8V, OVDD = 2.5V, 40MSPS clock, 50% clock duty cycle, -1dBFS 8MHz input signal, unless otherwise noted) Symbol Parameter Conditions Min Typ Max Units Performance SNR SINAD Signal to Noise Ratio Signal to Noise and Distortion Ratio 61.6 dBFS 61.6 dBFS FIN ≃ FS/2 61.6 dBFS FIN = 30MHz 61.5 dBFS FIN = 2MHz 61.6 dBFS FIN = 8MHz 60 FIN = 8MHz 61.6 dBFS FIN ≃ FS/2 60 61.2 dBFS FIN = 30MHz 61.4 dBFS 80 dBc 81 dBc 72.0 dBc FIN = 30MHz 80 dBc FIN = 2MHz -90 dBc -90 dBc FIN ≃ FS/2 -85 dBc FIN = 30MHz -85 dBc FIN = 2MHz -80 dBc -81 dBc FIN = 2MHz SFDR HD2 HD3 ENOB Spurious Free Dynamic Range Second order Harmonic Distortion Third order Harmonic Distortion Effective number of Bits FIN = 8MHz 70 FIN ≃ FS/2 FIN = 8MHz -80 FIN = 8MHz -70 FIN ≃ FS/2 -72.0 dBc FIN = 30MHz -80 dBc FIN = 2MHz 9.9 bits FIN = 8MHz 9.9 bits FIN ≃ FS/2 9.7 9.9 bits FIN = 30MHz 9.9 bits Power Supply AIDD Analog Supply Current DIDD Digital Supply Current Output Driver Supply mA 1.7 mA 2.5V output driver supply, sine wave input, FIN = 1MHz, CLK_EXT enabled 3.1 mA 2.5V output driver supply, sine wave input, FIN = 1MHz, CLK_EXT disabled 2.2 mA Analog Power Dissipation 16.7 mW Digital Power Dissipation OVDD = 2.5V, 5pF load on output bits, FIN = 1MHz, CLK_EXT disabled 8.6 mW Total Power Dissipation OVDD = 2.5V, 5pF load on output bits, FIN = 1MHz, CLK_EXT disabled 25.3 mW 9.7 µW Power Dissipation, Sleep mode 11.3 mW Power Down Dissipation Sleep Mode Clock Inputs Max. Conversion Rate 40 Min. Conversion Rate ©2009-2013 Exar Corporation MSPS 20 7/14 MSPS Rev 1B Rev 1B OIDD 9.3 Digital core supply CDK1308 Ultra Low Power, 20/40/65/80MSPS, 10-bit ADCs FIN = 2MHz Data Sheet Electrical Characteristics - CDK1308C (AVDD = 1.8V, DVDD = 1.8V, DVDDCLK = 1.8V, OVDD = 2.5V, 65MSPS clock, 50% clock duty cycle, -1dBFS 8MHz input signal, unless otherwise noted) Symbol Parameter Conditions Min Typ FIN = 8MHz 60 Max Units Performance Signal to Noise Ratio dBFS 61.6 dBFS FIN ≃ FS/2 61.5 dBFS FIN = 40MHz 61.3 dBFS 61.6 dBFS FIN = 20MHz 61.6 dBFS FIN ≃ FS/2 60.4 dBFS FIN = 40MHz 61.1 dBFS FIN = 8MHz SINAD Signal to Noise and Distortion Ratio 60 FIN = 8MHz SFDR Spurious Free Dynamic Range 77 dBc FIN = 20MHz 70 77 dBc FIN ≃ FS/2 70 dBc FIN = 40MHz 75 dBc -90 dBc FIN = 20MHz -95 dBc FIN ≃ FS/2 -85 dBc FIN = 40MHz -90 dBc -77 dBc FIN = 20MHz -77 dBc FIN ≃ FS/2 -70 dBc FIN = 40MHz -75 dBc 9.9 bits FIN = 20MHz 9.9 bits FIN ≃ FS/2 9.7 bits FIN = 40MHz 9.9 bits FIN = 8MHz HD2 Second order Harmonic Distortion -80 FIN = 8MHz HD3 Third order Harmonic Distortion -70 FIN = 8MHz ENOB Effective number of Bits 9.7 Power Supply AIDD Analog Supply Current DIDD Digital Supply Current mA 2.6 mA 2.5V output driver supply, sine wave input, FIN = 1MHz, CLK_EXT enabled 4.9 mA 2.5V output driver supply, sine wave input, FIN = 1MHz, CLK_EXT disabled 3.4 mA 24.8 mW Digital Power Dissipation OVDD = 2.5V, 5pF load on output bits, FIN = 1MHz, CLK_EXT disabled 13.2 mW Total Power Dissipation OVDD = 2.5V, 5pF load on output bits, FIN = 1MHz, CLK_EXT disabled 38.0 mW 9.3 µW Power Dissipation, Sleep mode 15.7 mW Output Driver Supply Analog Power Dissipation Power Down Dissipation Sleep Mode Clock Inputs Max. Conversion Rate 65 Min. Conversion Rate ©2009-2013 Exar Corporation MSPS 40 8/14 MSPS Rev 1B Rev 1B OIDD 13.8 Digital core supply CDK1308 Ultra Low Power, 20/40/65/80MSPS, 10-bit ADCs SNR 61.6 FIN = 20MHz Data Sheet Electrical Characteristics - CDK1308D (AVDD = 1.8V, DVDD = 1.8V, DVDDCLK = 1.8V, OVDD = 2.5V, 80MSPS clock, 50% clock duty cycle, -1dBFS 8MHz input signal, unless otherwise noted) Symbol Parameter Conditions Min Typ FIN = 8MHz 60 Max Units Performance Signal to Noise Ratio dBFS 61.2 dBFS FIN = 30MHz 61.3 dBFS FIN ≃ FS/2 61.3 dBFS 61.3 dBFS FIN = 20MHz 60.7 dBFS FIN = 30MHz 61.0 dBFS 59 dBFS FIN = 8MHz SINAD Signal to Noise and Distortion Ratio 60 FIN ≃ FS/2 FIN = 8MHz SFDR Spurious Free Dynamic Range 75 dBc FIN = 20MHz 70 75 dBc FIN = 30MHz 75 dBc FIN ≃ FS/2 65 dBc -90 dBc FIN = 20MHz -95.0 dBc FIN = 30MHz -90 dBc FIN ≃ FS/2 -80 dBc -75 dBc FIN = 20MHz -75.0 dBc FIN = 30MHz -75 dBc FIN ≃ FS/2 -65 dBc 9.9 bits FIN = 20MHz 9.8 bits FIN = 30MHz 9.8 bits FIN ≃ FS/2 9.5 bits FIN = 8MHz HD2 Second order Harmonic Distortion -80 FIN = 8MHz HD3 Third order Harmonic Distortion -70 FIN = 8MHz ENOB Effective number of Bits 9.7 Power Supply AIDD Analog Supply Current DIDD Digital Supply Current mA 3.3 mA 2.5V output driver supply, sine wave input, FIN = 1MHz, CLK_EXT enabled 5.9 mA 2.5V output driver supply, sine wave input, FIN = 1MHz, CLK_EXT disabled 4.1 mA 29.7 mW Digital Power Dissipation OVDD = 2.5V, 5pF load on output bits, FIN = 1MHz, CLK_EXT disabled 16.2 mW Total Power Dissipation OVDD = 2.5V, 5pF load on output bits, FIN = 1MHz, CLK_EXT disabled 45.9 mW 9.1 µW Power Dissipation, Sleep mode 18.3 mW Output Driver Supply Analog Power Dissipation Power Down Dissipation Sleep Mode Clock Inputs Max. Conversion Rate 80 Min. Conversion Rate ©2009-2013 Exar Corporation MSPS 65 9/14 MSPS Rev 1B Rev 1B OIDD 16.5 Digital core supply CDK1308 Ultra Low Power, 20/40/65/80MSPS, 10-bit ADCs SNR 61.6 FIN = 20MHz Data Sheet Digital and Timing Electrical Characteristics (AVDD = 1.8V, DVDD = 1.8V, DVDDCLK = 1.8V, OVDD = 2.5V, 20/40/65/80MSPS clock, 50% clock duty cycle, -1 dBFS input signal, 5pF capacitive load, unless otherwise noted) Symbol Parameter Conditions Min Typ Max Units 80 % high Clock Inputs 20 Compliance CMOS, LVDS, LVPECL, Sine Wave Differential input swing 400 Differential input swing, sine wave clock input 1.6 Input Common Mode Voltage Keep voltages within ground and voltage of OVDD 0.3 Input Capacitance Differential Input Range mVpp Vpp VOVDD -0.3 2 V pF Timing TPD Start Up Time from Power Down TSLP Start Up Time from Sleep TOVR Out Of Range Recovery Time TAP From Power Down Mode to Active Mode From Sleep Mode to Active Mode 900 clk cycles 20 clk cycles 1 clk cycles ns Aperture Delay 0.8 εRMS Aperture Jitter <0.5 ps TLAT Pipeline Delay 12 clk cycles TD Output Delay 5pF load on output bits (see timing diagram) 3 10 ns TDC Output Delay Relative to CLK_EXT See timing diagram 1 6 ns VOVDD ≥ 3.0V 2 Logic Inputs VIH High Level Input Voltage VOVDD = 1.7V – 3.0V V 0.8 • VOVDD V VOVDD ≥ 3.0V 0 0.8 V VOVDD = 1.7V – 3.0V 0 0.2 • VOVDD V VIL Low Level Input Voltage IIH High Level Input Leakage Current -10 10 µA IIL Low Level Input Leakage Current -10 10 µA CI Input Capacitance 3 pF Logic Outputs High Level Output Voltage VOL Low Level Output Voltage CL Max Capacitive Load VOVDD -0.1 V Post-driver supply voltage equal to pre-driver supply voltage VOVDD = VOCVDD Post-driver supply voltage above 2.25V (1) 10 0.1 V 5 pF pF Note: (1) The outputs will be functional with higher loads. However, it is recommended to keep the load on output data bits as low as possible to keep dynamic currents and resulting switching noise at a minimum. ©2009-2013 Exar Corporation 10/14 Rev 1B Rev 1B VOH CDK1308 Ultra Low Power, 20/40/65/80MSPS, 10-bit ADCs Duty Cycle Data Sheet N+3 N+4 N+5 N+2 N N+1 CLK_EXT Figure 1. Timing Diagram Recommended Usage DC-Coupling Analog Input Figure 3 shows a recommended configuration for DCcoupling. Note that the common mode input voltage must be controlled according to specified values. Preferably, the CM_EXT output should be used as a reference to set the common mode voltage. The analog inputs to the CDK1308 is a switched capacitor track-and-hold amplifier optimized for differential operation. Operation at common mode voltages at mid supply is recommended even if performance will be good for the ranges specified. The CM_EXT pin provides a voltage suitable as common mode voltage reference. The internal buffer for the CM_EXT voltage can be switched off, and driving capabilities can be changed by using the CM_EXTBC control input. 43Ω Rev 1B Figure 2 shows a simplified drawing of the input network. The signal source must have sufficiently low output impedance to charge the sampling capacitors within one clock cycle. A small external resistor (e.g. 22Ω) in series with each input is recommended as it helps reducing transient currents and dampens ringing behavior. A small differential shunt capacitor at the chip side of the resistors may be used to provide dynamic charging currents and may improve performance. The resistors form a low pass filter with the capacitor, and values must therefore be determined by requirements for the application. The input amplifier could be inside a companion chip or it could be a dedicated amplifier. Several suitable single ended to differential driver amplifiers exist in the market. The system designer should make sure the specifications of the selected amplifier is adequate for the total system, and that driving capabilities comply with the CDK1308 input specifications. 33pF 43Ω Figure 3. DC-Coupled Input Detailed configuration and usage instructions must be found in the documentation of the selected driver, and the values given in Figure 3 must be varied according to the recommendations for the driver. AC-Coupling Figure 2. Input Configuration ©2009-2013 Exar Corporation A signal transformer or series capacitors can be used to make an AC-coupled input network. Figure 4 shows 11/14 CDK1308 Ultra Low Power, 20/40/65/80MSPS, 10-bit ADCs N-13 Rev 1B Data Sheet Note that startup time from Sleep Mode and Power Down Mode will be affected by this filter as the time required to charge the series capacitors is dependent on the filter cut-off frequency. If the input signal has a long traveling distance, and the kickbacks from the ADC not are effectively terminated at the signal source, the input network of Figure 6 can be used. The configuration is designed to attenuate the kickback from the ADC and to provide an input impedance that looks as resistive as possible for frequencies below Nyquist. Values of the series inductor will however depend on board design and conversion rate. In some instances a shunt capacitor in parallel with the termination resistor (e.g. 33pF) may improve ADC performance further. This capacitor attenuate the ADC kick-back even more, and minimize the kicks traveling towards the source. However, the impedance match seen into the transformer becomes worse. 120nH 33Ω 1:1 33Ω RT 47Ω optional RT 68Ω 220Ω pF 120nH 33Ω 33Ω Figure 4. Transformer-Coupled Input Ω pF Ω Figure 5. AC-Coupled Input ©2009-2013 Exar Corporation Figure 6. Alternative Input Network Rev 1B Figure 5 shows AC-coupling using capacitors. Resistors from the CM_EXT output, RCM, should be used to bias the differential input signals to the correct voltage. The series capacitor, CI, form the high-pass pole with these resistors, and the values must therefore be determined based on the requirement to the high-pass cut-off frequency. Clock Input And Jitter Considerations Typically high-speed ADCs use both clock edges to generate internal timing signals. In the CDK1308 only the rising edge of the clock is used. Hence, input clock duty cycles between 20% and 80% is acceptable. The input clock can be supplied in a variety of formats. The clock pins are AC-coupled internally, and hence a wide common mode voltage range is accepted. Differential clock sources as LVDS, LVPECL or differential sine wave can be connected directly to the input pins. For CMOS inputs, the CLKN pin should be connected to ground, and the CMOS clock signal should be connected to CLKP. For differential sine wave clock input the amplitude must be at least ±800mVpp. 12/14 CDK1308 Ultra Low Power, 20/40/65/80MSPS, 10-bit ADCs a recommended configuration using a transformer. Make sure that a transformer with sufficient linearity is selected, and that the bandwidth of the transformer is appropriate. The bandwidth should exceed the sampling rate of the ADC with at least a factor of 10. It is also important to keep phase mismatch between the differential ADC inputs small for good HD2 performance. This type of transformer coupled input is the preferred configuration for high frequency signals as most differential amplifiers do not have adequate performance at high frequencies. If the input signal is traveling a long physical distance from the signal source to the transformer (for example a long cable), kickbacks from the ADC will also travel along this distance. If these kick-backs are not terminated properly at the source side, they are reflected and will add to the input signal at the ADC input. This could reduce the ADC performance. To avoid this effect, the source must effectively terminate the ADC kick-backs, or the traveling distance should be very short. If this problem could not be avoided, the circuit in Figure 6 can be used. Rev 1B Data Sheet The quality of the input clock is extremely important for high-speed, high-resolution ADCs. The contribution to SNR from clock jitter with a full scale signal at a given frequency is shown in the equation below: • π • FIN • εt) where FIN is the signal frequency, and εt is the total rms jitter measured in seconds. The rms jitter is the total of all jitter sources including the clock generation circuitry, clock distribution and internal ADC circuitry. For applications where jitter may limit the obtainable performance, it is of utmost importance to limit the clock jitter. This can be obtained by using precise and stable clock references (e.g. crystal oscillators with good jitter specifications) and make sure the clock distribution is well controlled. It might be advantageous to use analog power and ground planes to ensure low noise on the supplies to all circuitry in the clock distribution. It is of utmost importance to avoid crosstalk between the ADC output bits and the clock and between the analog input signal and the clock since such crosstalk often results in harmonic distortion. The jitter performance is improved with reduced rise and fall times of the input clock. Hence, optimum jitter performance is obtained with LVDS or LVPECL clock with fast edges. CMOS and sine wave clock inputs will result in slightly degraded jitter performance. Digital Outputs Digital output data are presented on parallel CMOS form. The digital outputs can be set in tristate mode by setting the OE_N signal high. The CDK1308 employs digital offset correction. This means that the output code will be 4096 with shorted inputs. However, small mismatches in parasitics at the input can cause this to alter slightly. The offset correction also results in possible loss of codes at the edges of the full scale range. With no offset correction, the ADC would clip in one end before the other, in practice resulting in code loss at the opposite end. With the output being centered digitally, the output will clip, and the out of range flags will be set, before max code is reached. When out of range flags are set, the code is forced to all ones for over-range and all zeros for under-range. Data Format Selection The output data are presented on offset binary form when DFRMT is low (connect to OVSS). Setting DFRMT high (connect to OVDD) results in 2’s complement output format. Details are shown in Table 1 below. Table 1: Data Format Description for 2Vpp Full Scale Range Differential Input Voltage (IP - IN) Output data: D_9 : D_0 Output Data: D_9 : D_0 (DFRMT = 0, offset binary) (DFRMT = 1, 2’s complement) 1.0 V 11 1111 1111 01 1111 1111 +0.24mV 10 0000 0000 00 0000 0000 -0.24mV 01 1111 1111 11 1111 1111 -1.0V 00 0000 0000 10 0000 0000 ©2009-2013 Exar Corporation 13/14 Rev 1B Rev 1B If the clock is generated by other circuitry, it should be retimed with a low jitter master clock as the last operation before it is applied to the ADC clock input. The timing is described in the Timing Diagram section. Note that the load or equivalent delay on CK_EXT always should be lower than the load on data outputs to ensure sufficient timing margins. CDK1308 Ultra Low Power, 20/40/65/80MSPS, 10-bit ADCs SNRjitter = 20 • log (2 The voltage on the OVDD pin set the levels of the CMOS outputs. The output drivers are dimensioned to drive a wide range of loads for OVDD above 2.25V, but it is recommended to minimize the load to ensure as low transient switching currents and resulting noise as possible. In applications with a large fanout or large capacitive loads, it is recommended to add external buffers located close to the ADC chip. Data Sheet Reference Voltages tributes to the Power Down Dissipation. The startup time from this mode is longer than for Sleep Mode as all references need to settle to their final values before normal operation can resume. The SLP_N signal can be used to set the full chip in Sleep Mode. In this mode internal clocking is disabled, but some low bandwidth circuitry is kept on to allow for a short startup time. However, Sleep Mode represents a significant reduction in supply current, and it can be used to save power even for short idle periods. Operational Modes The operational modes are controlled with the PD_N and SLP_N pins. If PD_N is set low, all other control pins are overridden and the chip is set in Power Down mode. In this mode all circuitry is completely turned off and the internal clock is disabled. Hence, only leakage current con- The input clock should be kept running in all idle modes. However, even lower power dissipation is possible in Power Down mode if the input clock is stopped. In this case it is important to start the input clock prior to enabling active mode. Mechanical Dimensions QFN-40 Package D D2 Pin 1 ID - Dia. 0.5 (Top Side) 1.14 Pin 1 ID - Dia. R F A G A3 0.45 A1 Pin 0 Exposed Pad Symbol A A1 A2 A3 b D D1 D2 L e θ1 F G R Min – 0.001 – 0.008 0.156 0.012 0° 0.008 0.0096 0.004 Inches Typ – 0.0004 0.023 0.008 REF 0.010 0.236 BSC 0.226 BSC 0.162 0.016 0.020 BSC – – 0.0168 0.008 Max 0.035 0.002 0.028 Min – 0.00 – 0.013 0.2 0.167 0.020 3.95 0.3 12° – 0.024 – 0° 0.2 0.24 0.1 Millimeters Typ – 0.01 0.65 0.2 REF 0.25 6.00 BSC 5.75 BSC 4.10 0.4 0.50 BSC – – 0.42 0.2 Max 0.9 0.05 0.7 0.32 4.25 0.5 12° – 0.6 – NOTE: D D2 D1 Package dimensions in millimeter unless otherwise noted. CDK1308 Ultra Low Power, 20/40/65/80MSPS, 10-bit ADCs The reference voltages are internally generated and buffered based on a bandgap voltage reference. No external decoupling is necessary, and the reference voltages are not available externally. This simplifies usage of the ADC since two extremely sensitive pins, otherwise needed, are removed from the interface. Rev 1B θ1 L e b A2 For Further Assistance: Exar Corporation Headquarters and Sales Offices 48720 Kato Road Tel.: +1 (510) 668-7000 Fremont, CA 94538 - USA Fax: +1 (510) 668-7001 www.exar.com NOTICE EXAR Corporation reserves the right to make changes to the products contained in this publication in order to improve design, performance or reliability. EXAR Corporation assumes no responsibility for the use of any circuits described herein, conveys no license under any patent or other right, and makes no representation that the circuits are free of patent infringement. Charts and schedules contained here in are only for illustration purposes and may vary depending upon a user’s specific application. While the information in this publication has been carefully checked; no responsibility, however, is assumed for inaccuracies. EXAR Corporation does not recommend the use of any of its products in life support applications where the failure or malfunction of the product can reasonably be expected to cause failure of the life support system or to significantly affect its safety or effectiveness. Products are not authorized for use in such applications unless EXAR Corporation receives, in writing, assurances to its satisfaction that: (a) the risk of injury or damage has been minimized; (b) the user assumes all such risks; (c) potential liability of EXAR Corporation is adequately protected under the circumstances. Reproduction, in part or whole, without the prior written consent of EXAR Corporation is prohibited. ©2009-2013 Exar Corporation 14/14 Rev 1B