ADC10D020 Dual 10-Bit, 20 MSPS, 150 mW A/D Converter General Description Features The ADC10D020 is a dual low power, high performance CMOS analog-to-digital converter that digitizes signals to 10 bits resolution at sampling rates up to 30 MSPS while consuming a typical 150 mW from a single 3.0V supply. No missing codes is guaranteed over the full operating temperature range. The unique two stage architecture achieves 9.5 Effective Bits over the entire Nyquist band at 20 MHz sample rate. An output formatting choice of straight binary or 2’s complement coding and a choice of two gain settings eases the interface to many systems. Also allowing great flexibility of use is a selectable 10-bit multiplexed or 20-bit parallel output mode. An offset correction feature minimizes the offset error. To ease interfacing to most low voltage systems, the digital output power pins of the ADC10D020 can be tied to a separate supply voltage of 1.5V to 3.6V, making the outputs compatible with other low voltage systems. When not converting, power consumption can be reduced by pulling the PD (Power Down) pin high, placing the converter into a low power state where it typically consumes less than 1 mW and from which recovery is less than 1 ms. Bringing the STBY (Standby) pin high places the converter into a standby mode where power consumption is about 27 mW and from which recovery is 800 ns. The ADC10D020’s speed, resolution and single supply operation makes it well suited for a variety of applications, including high speed portable applications. Operating over the industrial (−40˚ ≤ TA ≤ +85˚C) temperature range, the ADC10D020 is available in a 48-pin TQFP. An evaluation board is available to ease the design effort. n n n n n n n n © 2002 National Semiconductor Corporation DS200255 Internal sample-and-hold Internal reference capability Dual gain settings Offset correction Selectable straight binary or 2’s complement output Multiplexed or parallel output bus Single +2.7V to 3.6V operation Power down and standby modes Key Specifications Resolution 10 Bits Conversion Rate 20 MSPS ENOB 9.5 Bits (typ) DNL 0.35 LSB (typ) Conversion Latency Parallel Outputs 2.5 Clock Cycles — Multiplexed Outputs, I Data Bus 2.5 Clock Cycles — Multiplexed Outputs, Q Data Bus 3 Clock Cycles n PSRR 90 dB n Power Consumption — Normal Operation 150 mW (typ) < 1 mW (typ) — Power Down Mode — Fast Recovery Standby Mode 27 mW (typ) n n n n n Applications n n n n n n Digital Video CCD Imaging Portable Instrumentation Communications Medical Imaging Ultrasound www.national.com ADC10D020 Dual 10-Bit, 20 MSPS, 150 mW A/D Converter April 2002 ADC10D020 Connection Diagram 20025501 TOP VIEW Ordering Information www.national.com Industrial Temperature Range (−40˚C ≤ TA ≤ +85˚C) NS Package ADC10D020CIVS TQFP ADC10D020EVAL Evaluation Board 2 ADC10D020 Block Diagram 20025502 3 www.national.com ADC10D020 Pin Descriptions and Equivalent Circuits Pin No. Symbol Equivalent Circuit Description 48 47 I+ I− Analog inputs to “I” ADC. Nominal conversion range is 1.25V to 1.75V with GAIN pin low, or 1.0V to 2.0V with GAIN pin high. 37 38 Q+ Q− Analog inputs to “Q” ADC. Nominal conversion range is 1.25V to 1.75V with GAIN pin low, or 1.0V to 2.0V with GAIN pin high. VREF Analog Reference Voltage input. The voltage at this pin should be in the range of 0.8V to 1.5V. With 1.0V at this pin and the GAIN pin low, the full scale differential inputs are 1 VP-P. With 1.0V at this pin and the GAIN pin high, the full scale differential inputs are 2 VP-P. This pin should be bypassed with a minimum 1 µF capacitor. 45 VCMO This is an analog output which can be used as a reference source and/or to set the common mode voltage of the input. It should be bypassed with a minimum of 1 µF low ESR capacitor in parallel with a 0.1 µF capacitor. This pin has a nominal output voltage of 1.5V and has a 1 mA output source capability. 43 VRP Top of the reference ladder. Do not drive this pin. Bypass this pin with a 10 µF low ESR capacitor and a 0.1 µF capacitor. 44 VRN Bottom of the reference ladder. Do not drive this pin. Bypass this pin with a 10 µF low ESR capacitor and a 0.1 µF capacitor. 1 www.national.com 4 Pin No. 33 2 31 32 34 35 36 8 thru 27 28 40, 41 Symbol Equivalent Circuit (Continued) Description CLK Digital clock input for both converters. The analog inputs are sampled on the falling edge of this clock input. OS Output Bus Select. With this pin at a logic high, both the “I” and the “Q” data are present on their respective 10-bit output buses (Parallel mode of operation). When this pin is at a logic low, the “I” and “Q” data are multiplexed onto the “I” output bus and the “Q” output lines all remain at a logic low (multiplexed mode). OC Offset Correct pin. A low-to-high transition on this pin initiates an independent offset correction sequence for each converter, which takes 34 clock cycles to complete. During this time 32 conversions are taken and averaged. The result is subtracted from subsequent conversions. Each input pair should have 0V differential value during this entire 34 clock period. OF Output Format pin. When this pin is LOW the output format is Straight Binary. When this pin is HIGH the output format is 2’s complement. This pin may be changed asynchronously, but this will result in errors for one or two conversions. STBY Standby pin. The device operates normally with a logic low on this and the PD (Power Down) pin. With this pin at a logic high and the PD pin at a logic low, the device is in the standby mode where it consumes just 27 mW of power. It takes just 800 ns to come out of this mode after the STBY pin is brought low. PD Power Down pin that, when high, puts the converter into the Power Down mode where it consumes less than 1 mW of power. It takes less than 1 ms to recover from this mode after the PD pin is brought low. If both the STBY and PD pins are high simultaneously, the PD pin dominates. GAIN This pin sets the internal signal gain at the inputs to the ADCs. With this pin low the full scale differential input peak-to-peak signal is equal to VREF. With this pin high the full scale differential input peak-to-peak signal is equal to 2 x VREF. I0–I9 and Q0–Q9 3V TTL/CMOS-compatible Digital Output pins that provide the conversion results of the I and Q inputs. I0 and Q0 are the LSBs, I9 and Q9 are the MSBs. Valid data is present just after the rising edge of the CLK input in the Parallel mode. In the multiplexed mode, I-channel data is valid on I0 through I9 when the I/Q output is high and the Q-channel data is valid on I0 through I9 when the I/Q output is low. I/Q Output data valid signal. In the multiplexed mode, this pin transitions from low to high when the data bus transitions from Q-data to I-data, and from high to low when the data bus transitions from I-data to Q-data. In the Parallel mode, this pin transitions from low to high as the output data changes. VA Positive analog supply pin. This pin should be connected to a quiet voltage source of +2.7V to +3.6V. VA and VD should have a common supply and be separately bypassed with 10 µF to 50 µF capacitors in parallel with 0.1 µF capacitors. 5 www.national.com ADC10D020 Pin Descriptions and Equivalent Circuits ADC10D020 Pin Descriptions and Equivalent Circuits Pin No. Symbol Equivalent Circuit (Continued) Description VD Digital supply pin. This pin should be connected to a quiet voltage source of +2.7V to +3.6V. VA and VD should have a common supply and be separately bypassed with 10 µF to 50 µF capacitors in parallel with 0.1 µF capacitors. 6, 30 VDR Digital output driver supply pins. These pins should be connected to a voltage source of +1.5V to VD and be bypassed with 10 µF to 50 µF capacitors in parallel with 0.1 µF capacitors. 3, 39, 42, 46 AGND The ground return for the analog supply. AGND and DGND should be connected together close to the ADC10D020 package. 5 DGND The ground return for the digital supply. AGND and DGND should be connected together close to the ADC10D020 package. 7, 29 DR GND 4 www.national.com The ground return of the digital output drivers. 6 Operating Ratings (Notes 1, 2) (Notes 1, 2) Operating Temperature Range If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. VA, VD Supply Voltage Positive Supply Voltages Voltage on Any Pin GAIN = High VCM Input Common Mode Range See (Note 4) ESD Susceptibility (Note 5) Human Body Model Storage Temperature VREF/4 to (VA–VREF/4) GAIN = High VREF/2 to (VA–VREF/2) 0.8V to 1.5V Digital Input Pins Voltage Range 250V Soldering Temperature, Infrared, 10 sec. (Note 6) GAIN = Low VREF Voltage Range 2500V Machine Model ± VREF/2 ± VREF GAIN = Low ± 25 mA ± 50 mA Package Dissipation at TA = 25˚C +1.5V to VD VIN Differential Voltage Range −0.3V to (VA or VD +0.3V) Package Input Current (Note 3) +2.7V to +3.6V VDR Supply Voltage 3.8V Input Current at Any Pin (Note 3) −40˚C ≤ TA ≤ +85˚C −0.3V to (VA +0.3V) 235˚C −65˚C to +150˚C Converter Electrical Characteristics The following specifications apply for VA = VD = VDR = +3.0 VDC, VREF = 1.0 VDC, GAIN = OF = 0V, OS = 3.0V, VIN (ac coupled) = FSR = 1.0 VP-P, CL = 15 pF, fCLK = 20 MHz, 50% Duty Cycle, RS = 50Ω, trc = tfc < 4 ns, NOT offset corrected. Boldface limits apply for TA = TMIN to TMAX: all other limits TA = 25˚C (Note 7). Symbol Parameter Conditions Typical (Note 8) Limits (Note 9) Units (Limits) STATIC CONVERTER CHARACTERISTICS INL Integral Non-Linearity ± 0.65 ± 1.8 LSB(max) DNL Differential Non-Linearity ± 0.35 +1.2 −1.0 LSB(max) LSB(min) 10 Bits −5 +10 −16 LSB(max) LSB(min) +0.5 +1.5 −0.5 LSB(max) LSB(min) −4 +6 −14 %FS(max) %FS(min) Resolution with No Missing Codes Without Offset Correction VOFF Offset Error With Offset Correction GE Gain Error DYNAMIC CONVERTER CHARACTERISTICS ENOB SINAD SNR THD Effective Number of Bits Signal-to-Noise Plus Distortion Ratio Signal-to-Noise Ratio Total Harmonic Distortion fIN = 1.0 MHz, VIN = FSR −0.1 dB 9.5 Bits fIN = 4.7 MHz, VIN = FSR −0.1 dB 9.5 fIN = 9.5 MHz, VIN = FSR −0.1 dB 9.5 Bits fIN = 19.5 MHz, VIN = FSR −0.1 dB 9.5 Bits fIN = 1.0 MHz, VIN = FSR −0.1 dB 59 dB 9.0 Bits(min) fIN = 4.7 MHz, VIN = FSR −0.1 dB 59 fIN = 9.5 MHz, VIN = FSR −0.1 dB 59 dB fIN = 19.5 MHz, VIN = FSR −0.1 dB 59 dB 56 dB(min) fIN = 1.0 MHz, VIN = FSR −0.1 dB 59 fIN = 4.7 MHz, VIN = FSR −0.1 dB 59 dB fIN = 9.5 MHz, VIN = FSR −0.1 dB 59 dB fIN = 19.5 MHz, VIN = FSR −0.1 dB 59 dB 56 dB(min) fIN = 1.0 MHz, VIN = FSR −0.1 dB −73 fIN = 4.7 MHz, VIN = FSR −0.1 dB −73 fIN = 9.5 MHz, VIN = FSR −0.1 dB −73 dB fIN = 19.5 MHz, VIN = FSR −0.1 dB −73 dB 7 dB −62 dB(min) www.national.com ADC10D020 Absolute Maximum Ratings ADC10D020 Converter Electrical Characteristics (Continued) The following specifications apply for VA = VD = VDR = +3.0 VDC, VREF = 1.0 VDC, GAIN = OF = 0V, OS = 3.0V, VIN (ac coupled) = FSR = 1.0 VP-P, CL = 15 pF, fCLK = 20 MHz, 50% Duty Cycle, RS = 50Ω, trc = tfc < 4 ns, NOT offset corrected. Boldface limits apply for TA = TMIN to TMAX: all other limits TA = 25˚C (Note 7). Symbol HS2 HS3 SFDR IMD FPBW Parameter Second Harmonic Third Harmonic Spurious Free Dynamic Range Intermodulation Distortion Conditions Typical (Note 8) Limits (Note 9) Units (Limits) fIN = 1.0 MHz, VIN = FSR −0.1 dB −84 dB fIN = 4.7 MHz, VIN = FSR −0.1 dB −92 dB fIN = 9.5 MHz, VIN = FSR −0.1 dB −87 dB fIN = 19.5 MHz, VIN = FSR −0.1 dB −87 dB fIN = 1.0 MHz, VIN = FSR −0.1 dB −80 dB fIN = 4.7 MHz, VIN = FSR −0.1 dB −78 dB fIN = 9.5 MHz, VIN = FSR −0.1 dB −78 dB fIN = 19.5 MHz, VIN = FSR −0.1 dB −78 dB fIN = 1.0 MHz, VIN = FSR −0.1 dB 76 dB fIN = 4.7 MHz, VIN = FSR −0.1 dB 75 dB fIN = 9.5 MHz, VIN = FSR −0.1 dB 75 dB fIN = 19.5 MHz, VIN = FSR −0.1 dB 74 dB 65 dB fIN1 < 4.9 MHz, VIN = FSR −6.1 dB fIN2 < 5.1 MHz, VIN = FSR −6.1 dB Overrange Output Code (VIN+−VIN−) > 1.1V 1023 Underrange Output Code (VIN+−VIN−) < −1.1V 0 Full Power Bandwidth 140 MHz INTER-CHANNEL CHARACTERISTICS Crosstalk 1 MHz input to tested channel, 4.75 MHz input to other channel −90 dB Channel - Channel Aperture Delay Match fIN = 8 MHz 8.5 ps 0.03 %FS 1 VP-P Channel - Channel Gain Matching REFERENCE AND ANALOG CHARACTERISTICS VIN Analog Differential Input Range CIN Analog Input Capacitance (each input) RIN Gain Pin = AGND Gain Pin = VA 2 VP-P Clock High 6 pF Clock Low 3 pF Analog Differential Input Resistance 27 kΩ VREF Reference Voltage 1.0 IREF Reference Input Current <1 VCMO Common Mode Voltage Output TC VCMO Common Mode Voltage Temperature Coefficient 1 mA load to ground (sourcing current) 1.5 0.8 V(min) 1.5 V(max) µA 1.35 V(min) 1.6 V(max) 20 ppm/˚C DIGITAL INPUT CHARACTERISTICS VIH Logical “1” Input Voltage VD = +2.7V 2.0 V(min) VIL Logical “0” Input Voltage VD = +3.6V 0.5 V(max) IIH Logical “1” Input Current VIH = VD IIL Logical “0” Input Current VIL = DGND <1 > −1 µA µA DIGITAL OUTPUT CHARACTERISTICS VOH Logical “1” Output Voltage VDR = +2.7V, IOUT = −0.5 mA VDR −0.3V V(min) VOL Logical “0” Output Voltage VDR = +2.7V, IOUT = 1.6 mA 0.4 V(max) www.national.com 8 (Continued) The following specifications apply for VA = VD = VDR = +3.0 VDC, VREF = 1.0 VDC, GAIN = OF = 0V, OS = 3.0V, VIN (ac coupled) = FSR = 1.0 VP-P, CL = 15 pF, fCLK = 20 MHz, 50% Duty Cycle, RS = 50Ω, trc = tfc < 4 ns, NOT offset corrected. Boldface limits apply for TA = TMIN to TMAX: all other limits TA = 25˚C (Note 7). Symbol Parameter Typical (Note 8) Conditions +ISC Output Short Circuit Source Current VOUT = 0V −ISC Output Short Circuit Sink Current VOUT = VDR Limits (Note 9) Units (Limits) Parallel Mode −7 mA Multiplexed Mode −14 mA Parallel Mode 7 mA Multiplexed Mode 14 mA POWER SUPPLY CHARACTERISTICS PD = LOW, STBY = LOW, dc input IA + ID IDR PWR Core Supply Current Digital Output Driver Supply Current (Note 10) Power Consumption 47.6 55 mA(max) PD = LOW, STBY = HIGH 8.8 mA PD = HIGH, STBY = LOW or HIGH 0.22 mA PD = LOW, STBY = LOW, dc input 1.3 1.4 mA(max) PD = LOW, STBY = HIGH 0.1 mA PD = HIGH, STBY = LOW or HIGH 0.1 mA PD = LOW, STBY = LOW, dc input 150 PD = LOW, STBY = LOW, 1 MHz Input 178 169 mW(max) mW PD = LOW, STBY = HIGH 27 mW PD = HIGH, STBY = LOW or HIGH <1 mW PSRR1 Power Supply Rejection Ratio Change in Full Scale with 2.7V to 3.6V Supply Change 90 dB PSRR2 Power Supply Rejection Ratio Rejection at output with 20 MHz, 250 mVP-P Riding on VA and VD 52 dB AC Electrical Characteristics OS = Low (Multiplexed Mode) The following specifications apply for VA = VD = VDR = +3.0VDC, VREF = 1.0 VDC, GAIN = OF = 0V, OS = 0V, VIN (ac coupled) = FSR = 1.0 VP-P, CL = 15 pF, fCLK = 20 MHz, 50% Duty Cycle, RS = 50Ω, trc = tfc < 4 ns, NOT offset corrected. Boldface limits apply for TA = TMIN to TMAX: all other limits TA = 25˚C (Note 7) Symbol Parameter Conditions Typical (Note 8) Limits (Note 9) Units (Limits) 20 MHz(min) fCLK1 Maximum Clock Frequency 30 fCLK2 Minimum Clock Frequency 1 Duty Cycle 50 MHz 30 70 %(min) %(max) Pipeline Delay (Latency) I Data 2.5 Clock Cycles Q Data 3.0 Clock Cycles 10 ns(min) 18 ns(max) tr, tf Output Rise and Fall Times tOC Offset Correction Pulse Width tOD Output Delay from CLK Edge to Data Valid 4 13 ns tDIQ I/Q Output Delay 13 tSKEW I/Q to Data Delay ± 200 ps tAD Sampling (Aperture) Delay 2.4 ns tAJ Aperture Jitter < 10 ps(rms) tVALID Data Valid Time 21 ns 50 ns <1 ms Overrange Recovery Time tWUPD Differential VIN step from 1.5V to 0V PD Low to 1/2 LSB Accurate Conversion (Wake-Up Time) 9 ns www.national.com ADC10D020 Converter Electrical Characteristics ADC10D020 AC Electrical Characteristics OS = Low (Multiplexed Mode) (Continued) The following specifications apply for VA = VD = VDR = +3.0VDC, VREF = 1.0 VDC, GAIN = OF = 0V, OS = 0V, VIN (ac coupled) = FSR = 1.0 VP-P, CL = 15 pF, fCLK = 20 MHz, 50% Duty Cycle, RS = 50Ω, trc = tfc < 4 ns, NOT offset corrected. Boldface limits apply for TA = TMIN to TMAX: all other limits TA = 25˚C (Note 7) Symbol tWUSB Parameter Conditions STBY Low to 1/2 LSB Accurate Conversion (Wake-Up Time) AC Electrical Characteristics Typical (Note 8) Limits (Note 9) 800 Units (Limits) ns OS = High (Parallel Mode) The following specifications apply for VA = +3.0 VDC, VD = +3.0 VDC, VDR = +3.0VDC, VREF = 1.0 VDC, GAIN = OF = 0V, OS = 3.0V, VIN (ac coupled) = FSR = 1.0 VP-P, CL = 15 pF, fCLK = 20 MHz, 50% Duty Cycle, RS = 50Ω, trc = tfc < 4 ns, NOT offset corrected. Boldface limits apply for TA = TMIN to TMAX: all other limits TA = 25˚C (Note 7) Symbol Parameter Conditions Typical (Note 8) Limits (Note 9) Units (Limits) 20 MHz(min) 30 70 %(min) %(max) 2.5 Conv Cycles fCLK1 Maximum Clock Frequency 30 fCLK2 Minimum Clock Frequency 1 Duty Cycle 50 Pipeline Delay (Latency) tr, tf Output Rise and Fall Times MHz 7 ns toc OC Pulse Width tOD Output Delay from CLK Edge to Data Valid 15 tDIQ I/Q Output Delay 13 tAD Sampling (Aperture) Delay 2.4 ns tAJ Aperture Jitter < 10 ps(rms) tVALID Data Valid Time 43 ns 50 ns Overrange Recovery Time Differential VIN step from 1.5V to 0V 10 ns 21 ns(max) ns tWUPD PD Low to 1/2 LSB Accurate Conversion (Wake-Up Time) <1 ms tWUSB STBY Low to 1/2 LSB Accurate Conversion (Wake-Up Time) 800 ns Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics. The guaranteed specifications apply only for the test conditions listed. Some performance characteristics may degrade when the device is not operated under the listed test conditions. Note 2: All voltages are measured with respect to GND = AGND = DGND = 0V, unless otherwise specified. Note 3: When the input voltage at any pin exceeds the power supplies (VIN < GND or VIN > VA or VD), the current at that pin should be limited to 25 mA. The 50 mA maximum package input current rating limits the number of pins that can safely exceed the power supplies with an input current of 25 mA to two. Note 4: The absolute maximum junction temperature (TJmax) for this device is 150˚C. The maximum allowable power dissipation is dictated by TJmax, the junction-to-ambient thermal resistance (θJA), and the ambient temperature (TA), and can be calculated using the formula PDMAX = (TJmax - TA )/θJA. In the 48-pin TQFP, θJA is 76˚C/W, so PDMAX = 1,645 mW at 25˚C and 855 mW at the maximum operating ambient temperature of 85˚C. Note that the power dissipation of this device under normal operation will typically be about 170 mW (150 mW quiescent power + 20 mW due to 1 LVTTL load on each digital output). The values for maximum power dissipation listed above will be reached only when the ADC10D020 is operated in a severe fault condition (e.g. when input or output pins are driven beyond the power supply voltages, or the power supply polarity is reversed). Obviously, such conditions should always be avoided. Note 5: Human body model is 100 pF capacitor discharged through a 1.5 kΩ resistor. Machine model is 220 pF discharged through 0Ω. Note 6: See AN450, “Surface Mounting Methods and Their Effect on Product Reliability”, or the section entitled “Surface Mount” found in any post 1986 National Semiconductor Linear Data Book, for other methods of soldering surface mount devices. Note 7: The inputs are protected as shown below. Input voltage magnitude up to 300 mV beyond the supply rails will not damage this device. However, errors in the A/D conversion can occur if the input goes beyond the limits given in these tables. www.national.com 10 OS = High (Parallel Mode) ADC10D020 AC Electrical Characteristics (Continued) 20025506 Note 8: Typical figures are at TJ = 25˚C, and represent most likely parametric norms. Note 9: Test limits are guaranteed to National’s AOQL (Average Outgoing Quality Level). Performance is guaranteed only at VREF = 1.0V and a clock duty cycle of 50%. The limits for VREF and clock duty cycle specify the range over which reasonable performance is expected. Tests are performed and limits guaranteed with clock low and high levels of 0.3V and VD − 0.3V, respectively. Note 10: IDR is the current consumed by the switching of the output drivers and is primarily determined by the load capacitance on the output pins, the supply voltage, VDR, and the rate at which the outputs are switching (which is signal dependent). IDR = VDR (CO x fO + C1 x f1 + ... + C9 x f9) where VDR is the output driver power supply voltage, Cn is the total capacitance on the output pin, and fn is the average frequency at which that pin is toggling. Timing Diagrams 20025508 ADC10D020 Timing Diagram for Multiplexed Mode 11 www.national.com ADC10D020 Timing Diagrams (Continued) 20025507 ADC10D020 Timing Diagram for Parallel Mode 20025509 FIGURE 1. AC Test Circuit www.national.com 12 APERTURE (SAMPLING) DELAY is that time required after the fall of the clock input for the sampling switch to open. The Sample/Hold circuit effectively stops capturing the input signal and goes into the “hold” mode tAD after the clock goes low. OFFSET ERROR is a measure of how far the mid-scale transition point is from the ideal zero voltage input. OUTPUT DELAY is the time delay after the rising edge of the input clock before the data update is present at the output pins. OVERRANGE RECOVERY TIME is the time required after the differential input voltages goes from 1.5V to 0V for the converter to recover and make a conversion with its rated accuracy. PIPELINE DELAY (LATENCY) is the number of clock cycles between initiation of conversion and when that data is presented to the output driver stage. New data is available at every clock cycle, but the data output lags the input by the Pipelined Delay plus the Output Delay. POWER SUPPLY REJECTION RATIO (PSRR) can be one of two specifications. PSRR1 (DC PSRR) is the ratio of the change in full scale gain error that results from a power supply voltage change from 2.7V to 3.6V. PSRR2 (AC PSRR) is measured with a 20 MHz, 250 mVP-P signal riding upon the power supply and is the ratio of the signal amplitude on the power supply pins to the amplitude of that frequency at the output. PSRR is expressed in dB. SIGNAL TO NOISE RATIO (SNR) is the ratio, expressed in dB, of the rms value of the fundamental signal at the output to the rms value of the sum of all other spectral components below one-half the sampling frequency, not including harmonics or dc. SIGNAL TO NOISE PLUS DISTORTION (S/(N+D) or SINAD) is the ratio, expressed in dB, of the rms value of the fundamental signal at the output to the rms value of all of the other spectral components below half the clock frequency, including harmonics but excluding dc. SPURIOUS FREE DYNAMIC RANGE (SFDR) is the difference, expressed in dB, between the rms values of the fundamental signal at the output and the peak spurious signal, where a spurious signal is any signal present in the output spectrum that is not present at the input. TOTAL HARMONIC DISTORTION (THD) is the ratio, expressed in dB, of the rms total of the first 9 harmonic levels to the level of the input frequency. THD is calculated as APERTURE JITTER is the variation in aperture delay from sample to sample. Aperture jitter shows up as input noise. CLOCK DUTY CYCLE is the ratio of the time that the clock waveform is high to the total time of one clock period. CROSSTALK is coupling of energy from one channel into the other channel. DIFFERENTIAL NON-LINEARITY (DNL) is the measure of the maximum deviation from the ideal step size of 1 LSB. Measured at 20 MSPS with a ramp input. EFFECTIVE NUMBER OF BITS (ENOB, or EFFECTIVE BITS) is another method of specifying Signal-to-Noise and Distortion Ratio, or SINAD. ENOB is defined as (SINAD − 1.76)/6.02 and says that the converter is equivalent to a perfect ADC of this (ENOB) number of bits. FULL POWER BANDWIDTH (FPBW) is the frequency at which the magnitude of the reconstructed output fundamental drops 3 dB below its 1 MHz value. GAIN ERROR is the difference between the ideal and actual differences between the input levels at which the first and last code transitions occur. That is, how far this difference is from Full Scale. INTEGRAL NON LINEARITY (INL) is a measure of the maximum deviation of each individual code from a line drawn from zero scale (1⁄2 LSB below the first code transition) through positive full scale (1⁄2 LSB above the last code transition). The deviation of any given code from this straight line is measured from the center of that code value. The end point test method is used. Measured at 20 MSPS with a ramp input. INTERMODULATION DISTORTION (IMD) is the creation of spectral components that are not present in the input as a result of two sinusoidal frequencies being applied to the ADC input at the same time. It is defined as the ratio of the power in the second and third order intermodulation products to the total power in one of the original frequencies. IMD is usually expressed in dB. LSB (LEAST SIGNIFICANT BIT) is the bit that has the smallest value of weight of all bits. This value is m * VREF/2n where “m” is the reference scale factor and “n” is the ADC resolution, which is 10 in the case of the ADC10D020. The value of “m” is determined by the logic level at the gain pin and has a value of 1 when the gain pin is at a logic low and a value of 2 when the gain pin is at a logic high. MISSING CODES are those output codes that are skipped or will never appear at the ADC outputs. These codes cannot be reached with any input value. where f1 is the RMS power of the fundamental (output) frequency and f2 through f10 are the RMS power of the first 9 harmonic frequencies in the output spectrum. 13 www.national.com ADC10D020 MSB (MOST SIGNIFICANT BIT) is the bit that has the largest value or weight. Its value is one half of full scale. Specification Definitions ADC10D020 Typical Performance Characteristics VA = VD = VDR = 3.0V, fCLK = 20 MHz, unless otherwise specified Typical INL INL vs. Supply Voltage 20025511 20025512 INL vs. VREF INL vs. fCLK 20025513 20025514 INL vs. Clock Duty Cycle INL vs. Temperature 20025516 20025515 www.national.com 14 VA = VD = VDR = 3.0V, fCLK = 20 MHz, unless otherwise specified (Continued) Typical DNL DNL vs. Supply Voltage 20025517 20025518 DNL vs. VREF DNL vs. fCLK 20025519 20025520 DNL vs. Clock Duty Cycle DNL vs. Temperature 20025521 20025522 15 www.national.com ADC10D020 Typical Performance Characteristics ADC10D020 Typical Performance Characteristics VA = VD = VDR = 3.0V, fCLK = 20 MHz, unless otherwise specified (Continued) SNR vs. Supply Voltage SNR vs. VREF @ fIN = 1 MHz to 9.5 MHz @ fIN = 4.7 MHz 20025523 20025524 SNR vs. fCLK @ fIN = 9.5 MHz SNR vs. fIN 20025525 20025526 SNR vs. Clock Duty Cycle @ fIN = 4.7 MHz SNR vs. VDR @ fIN = 9.5 MHz 20025527 www.national.com 20025528 16 VA = VD = VDR = 3.0V, fCLK = 20 MHz, unless otherwise specified (Continued) SNR vs. VCM @ fIN = 9.5 MHz SNR vs. Temperature @ fIN = 1 MHz to 9.5 MHz 20025530 20025529 SINAD & ENOB vs. Supply Voltage @ fIN = 1 MHz to 9.5 MHz SINAD & ENOB vs. VREF @ fIN = 4.7 MHz 20025531 20025532 SINAD & ENOB vs. @ fCLK (fIN = 9.5 MHz) SINAD & ENOB vs. fIN 20025533 20025534 17 www.national.com ADC10D020 Typical Performance Characteristics ADC10D020 Typical Performance Characteristics VA = VD = VDR = 3.0V, fCLK = 20 MHz, unless otherwise specified (Continued) SINAD & ENOB vs. Clock Duty Cycle @ fIN = 4.7 MHz SINAD & ENOB vs. VDR @ fIN = 9.5 MHz 20025535 20025536 SINAD & ENOB vs. Temperature @ fIN = 1 MHz to 9.5 MHz SINAD & ENOB vs. VCM @ fIN = 9.5 MHz 20025538 20025537 Distortion vs. Supply Voltage @ fIN = 4.7 MHz Distortion vs. VREF @ fIN = 4.7 MHz 20025539 www.national.com 20025540 18 VA = VD = VDR = 3.0V, fCLK = 20 MHz, unless otherwise specified (Continued) Distortion vs. fCLK @ fIN = 9.5 MHz Distortion vs. fIN 20025541 20025542 Distortion vs. Clock Duty Cycle @ fIN = 4.7 MHz Distortion vs. VDR @ fIN = 4.7 MHz 20025543 20025544 Distortion vs. VCM @ fIN = 4.7 MHz Distortion vs. Temperature 20025546 20025545 19 www.national.com ADC10D020 Typical Performance Characteristics ADC10D020 Typical Performance Characteristics VA = VD = VDR = 3.0V, fCLK = 20 MHz, unless otherwise specified (Continued) SFDR vs. Supply Voltage @ fIN = 4.7 MHz SFDR vs. VREF @ fIN = 4.7 MHz 20025547 20025548 SFDR vs. fCLK @ fIN = 9.5 MHz SFDR vs. fIN 20025549 20025550 SFDR vs. Clock Duty Cycle @ fIN = 4.7 MHz SFDR vs. VDR @ fIN = 4.7 MHz 20025551 www.national.com 20025552 20 VA = VD = VDR = 3.0V, fCLK = 20 MHz, unless otherwise specified (Continued) SFDR vs. VCM @ fIN = 4.7 MHz SFDR vs. Temperature @ fIIN = 4.7 MHz 20025554 20025553 Crosstalk vs. VDR @ fIN = 4.7 MHz Crosstalk vs. fIN 20025555 20025556 Crosstalk vs. VCM @ fIN = 4.7 MHz Crosstalk vs. Temperature 20025558 20025557 21 www.national.com ADC10D020 Typical Performance Characteristics ADC10D020 Typical Performance Characteristics VA = VD = VDR = 3.0V, fCLK = 20 MHz, unless otherwise specified (Continued) Spectral Response @ fIN = 1 MHz Power Consumption vs. Temperature 20025561 20025562 Spectral Response @ fIN = 4.7 MHz Spectral Response @ fIN = 9.5 MHz 20025563 20025564 Spectral Response @ fIN = 21 MHz Spectral Response @ fIN = 49 MHz 20025565 www.national.com 20025566 22 VA = VD = VDR = 3.0V, fCLK = 20 MHz, unless otherwise specified (Continued) Spectral Response @ fIN = 99 MHz IMD Response @ fIN = 4.9 MHz, 5.1 MHz 20025581 20025568 Functional Description Applications Information Using a subranging architecture, the ADC10D020 achieves 9.5 effective bits over the entire Nyquist band at 20 MSPS while consuming just 150 mW. The use of an internal sample-and-hold amplifier (SHA) not only enables this sustained dynamic performance, but also lowers the converter’s input capacitance and reduces the number of external components required. Analog signals at the “I” and “Q” inputs that are within the voltage range set by VREF and the GAIN pin are digitized to ten bits at up to 30 MSPS. VREF has a range of 0.8V to 1.5V, providing a differential peak-to-peak input range of 0.8 VP-P to 1.5 VP-P with the GAIN pin at a logic low, or an input range of 1.6 VP-P to 3.0 VP-P with the GAIN pin at a logic high. Differential input voltages less than −VREF/2 with the GAIN pin low, or less than −VREF with the GAIN pin high will cause the output word to indicate a negative full scale. Differential input voltages greater than VREF/2 with the GAIN pin low, or greater than VREF with the GAIN pin high, will cause the output word to indicate a positive full scale. Both “I” and “Q” channels are sampled simultaneously on the falling edge of the clock input, while the timing of the data output depends upon the mode of operation. In the parallel mode, the “I” and “Q” output busses contain the conversion result for their respective inputs. The “I” and “Q” channel data are present and valid at the data output pins tOD after the rising edge of the input clock. In the multiplexed mode, “I” channel data is available at the digital outputs tOD after the rise of the clock edge, while the “Q” channel data is available at the digital outputs tOD after the fall of the clock. However, a delayed I/Q output signal should be used to latch the output for best, most consistent results. Data latency in the parallel mode is 2.5 clock cycles. In the multiplexed mode data latency is 2.5 clock cycles for the “I” channel and 3.0 clock cycles for the “Q” channel. The ADC10D020 will convert as long as the clock signal is present and the PD and STBY pins are low. Throughout this discussion,VCM refers to the Common Mode input voltage of the ADC10D020 while VCMO refers to its Common Mode output voltage. 1.0 THE ANALOG SIGNAL INPUTS Each of the analog inputs of the ADC10D020 consists of a switch (transmission gate) followed by a switched capacitor amplifier. The capacitance seen at each input pin changes with the clock level, appearing as about 3 pF when the clock is low, and about 6 pF when the clock is high. A switched capacitance is harder to drive than is a larger, fixed capacitance. The CLC409 and the CLC428 dual op amp have been found to be a good amplifiers to drive the ADC10D020 because of their wide bandwidth and low distortion. They also have good Differential Gain and Differential Phase performance. Care should be taken to avoid driving the inputs beyond the supply rails, even momentarily, as during power-up. The ADC10D020 is designed for differential input signals for best performance. With a 1.0V reference and the GAIN pin at a logic low, differential input signals up to 1.0 VP-P are digitized. See Figure 2. For differential signals, the input common mode is expected to be about 1.5V, but the inputs are not sensitive to the common-mode voltage and can be anywhere within the supply rails (ground to VA) with little or no performance degradation, as long as the signal swing at the individual input pins is no more than 300 mV beyond the supply rails. For single ended drive, operate the ADC10D020 with the GAIN pin at a logic low, connect one pin of the input pair to 1.5V (VCM) and drive the other pin of the input pair with 1.0 VP-P centered around 1.5V. Because of the larger signal swing at one input for single-ended operation, distortion performance will not be as good as with a differential input signal. Alternatively, single-ended to differential conversion with a transformer provides a quick, easy solution for those applications not requiring response to dc and low frequencies. See Figure 3. The 36Ω resistors and 110 pF capacitor values are chosen to provide a cutoff frequency near the clock frequency to compensate for the effects of input sampling. A lower time constant should be used for undersampling applications. 23 www.national.com ADC10D020 Typical Performance Characteristics ADC10D020 Applications Information Figure 4 shows a simple reference biasing scheme with minimal components. While this circuit will suffice for many applications, the value of the reference voltage will depend upon the supply voltage. (Continued) The circuit of Figure 5 is an improvement over the circuit of Figure 4 because the reference voltage is independent of supply voltage. This reduces problems of reference voltage variability. The reference voltage at the VREF pin should be bypassed to AGND with a 5 µF (or larger) tantalum or electrolytic capacitor and a 0.1 µF ceramic capacitor. The circuit of Figure 6 may be used if it is desired to obtain a precise reference voltage not available with a fixed reference source. The 240Ω and 1k resistors can be replaced with a potentiometer, if desired. 20025569 FIGURE 2. The ADC10D020 is designed for use with differential signals of 1.0 VP-P with a common mode voltage of 1.5V. The signal swing should not cause any pin to experience a swing more than 300 mV beyond the supply rails. 20025570 2.0 REFERENCE INPUTS The VRP and VRN pins should each be bypassed with a 5 µF (or larger) tantalum or electrolytic capacitor and a 0.1 µF ceramic capacitor. Use these pins only for bypassing. DO NOT connect anything else to these pins. www.national.com FIGURE 3. Use of an input transformer for single-ended to differential conversion can simplify circuit design for single-ended signals. 24 ADC10D020 Applications Information (Continued) 20025571 FIGURE 4. Simple Reference Biasing 25 www.national.com ADC10D020 Applications Information (Continued) 20025572 FIGURE 5. Improved Low Component Count Reference Biasing The VCMO output can be used as the ADC reference source as long as care is taken to prevent excessive loading of this pin. However, the VCMO output was not designed to be a precision reference and has more variability than does a precision reference. Refer to VCMO, Common Mode Voltage Output, in the Electrical Characteristics table. Since the reference input of the ADC10D020 is buffered, there is virtually no loading on the VCMO output by the VREF pin. While the ADC10D020 will work with a 1.5V reference voltage, it is fully www.national.com specified for a 1.0V reference. To use the VCMO for a reference voltage at 1.0V, the 1.5V VCMO output needs to be divided down. The divider resistor values need to be carefully chosen to prevent excessive VCMO loading. See Figure 7. While the average temperature coefficient of VCMO is 20 ppm/˚C, that temperature coefficient can be broken down to a typical 50 ppm/˚C between −40˚C and +25˚C and a typical −12 ppm/˚C between +25˚C and +85˚C. 26 ADC10D020 Applications Information (Continued) 20025573 FIGURE 6. Setting An Accurate Reference Voltage 27 www.national.com ADC10D020 Applications Information (Continued) 20025574 FIGURE 7. The VCMO output pin may be used as an internal reference source if its output is divided down and not loaded excessively. 2.1 REFERENCE VOLTAGE The reference voltage should be within the range specified in the Operating Ratings table (0.8V to 1.5V). A reference voltage that is too low could result in a noise performance that is less than desired because the quantization level falls below other noise sources. On the other hand, a reference voltage that is too high means that an input signal that produces a full scale output uses such a large input range that the input stage is less linear, resulting in a degradation of distortion performance. Also, for large reference voltages, the internal ladder buffer runs out of head-room, leading to a reduction of gain in that buffer and causing gain error degradation. The Reference bypass pins VRP and VRN are output compensated and should each be bypassed with a parallel combination of a 5 µF (minimum) and 0.1 µF capacitors. As mentioned in the previous section, the VCMO output can be used as the ADC reference. www.national.com 2.2 VCMO OUTPUT The VCMO output pin is intended to provide a common mode bias for the differential input pins of the ADC10D020. It can also be used as a voltage reference source. Care should be taken, however, to avoid loading this pin with more than 1 mA. A load greater than this could result in degraded long term and temperature stability of this voltage. The VCMO pin is output compensated and should be bypassed with a 2 µF/0.1 µF combination, minimum. See 2.0 REFERENCE INPUTS for more information on using the VCMO output as a reference source. 3.0 DIGITAL INPUT PINS The seven digital input pins are used to control the function of the ADC10D020. 28 Each input pair should have a 0V differential voltage value during this entire 34 clock period, but the “I” and “Q” input common mode voltages do not have to be equal to each other. Because of the uncertainty as to exactly when the correction sequence starts, it is best to allow 35 clock periods for this sequence. (Continued) 3.1 CLOCK (CLK) INPUT The clock (CLK) input is common to both A/D converters. This pin is CMOS/LVTTL compatible with a threshold of about VA/2. Although the ADC10D020 is tested and its performance is guaranteed with a 20 MHz clock, it typically will function well with low-jitter clock frequencies from 1 MHz to 30 MHz. The clock source should be series terminated to match the source impedance with the characteristic impedance, ZO, of the clock line and the ADC clock pin should be AC terminated, near the clock input, with a series RC to ground. The resistor value should equal the characteristic impedance, ZO, of the clock line and the capacitor should have a value such that C x ZO ≥ 4 x tPD, where tPD is the time of propagation of the clock signal from its source to the ADC clock pin. The typical propagation rate on a board of FR4 material is about 150 ps/inch. The rise and fall times of the clock supplied to the ADC clock pin should be no more than 2 ns. The analog inputs I = (I+) – (I−) and Q = (Q+) – (Q−) are simultaneously sampled on the falling edge of this input to ensure the best possible aperture delay match between the two channels. 3.4 OUTPUT FORMAT (OF) PIN The Output Format (OF) pin provides a choice of straight binary or 2’s complement output formatting. With this pin at a logic low, the output format is straight binary. With this pin at a logic high, the output format is 2’s complement. 3.5 STANDBY (STBY) PIN The Standby (STBY) pin may be used to put the ADC10D020 into a low power mode where it consumes just 27 mW and can quickly be brought to full operation. The device operates normally with a logic low on this and the PD pins. 3.6 POWER DOWN (PD) PIN The Power Down (PD) pin puts the device into a low-power “sleep” state where it consumes less than 1 mW when the PD pin is at a logic high. Power consumption is reduced more when the PD pin is high than when the STBY pin is high, but recovery to full operation is much quicker from the standby state than it is from the power down state. When the STBY and PD pins are both high, the ADC10D020 is in the power down mode. 3.2 OUTPUT BUS SELECT (OS) PIN The Output Bus Select (OS) pin determines whether the ADC10D020 is in the parallel or multiplexed mode of operation. A logic high at this pin puts the device into the parallel mode of operation where “I” and “Q” data appear at their respective output buses. A logic low at this pin puts the device into the multiplexed mode of operation where the “I” and “Q” data are multiplexed onto the “I” output bus and the “Q” output lines all remain at a logic low. 3.7 GAIN PIN The GAIN pin sets the internal signal gain of the “I” and “Q” inputs. With this pin at a logic low, the full scale differential peak-to-peak input signal is equal to VREF. With the GAIN pin at a logic high, the full scale differential peak-to-peak input signal is equal to 2 times VREF. 3.3 OFFSET CORRECT (OC) PIN The Offset Correct (OC) pin is used to initiate an offset correction sequence. This procedure should be done after power up and need not be performed again unless power to the ADC10D020 is interrupted. An independent offset correction sequence for each converter is initiated when there is a low-to-high transition at the OC pin. This sequence takes 34 clock cycles to complete, during which time 32 conversions are taken and averaged. The result is subtracted from subsequent conversions. Because the offset correction is performed digitally at the output of the ADC, the output range of the ADC is reduced by the offset amount. 4.0 INPUT/OUTPUT RELATIONSHIP ALTERNATIVES The GAIN pin of the ADC10D020 offers input range selection, while the OF pin offers a choice of straight binary or 2’s complement output formatting. The relationship between the GAIN, OF, analog inputs and the output code are as defined in Table 1. Keep in mind that the input signals must not exceed the power supply rails. TABLE 1. ADC10D020 Input/Output Relationships GAIN OF I+/Q+ I−/Q− Output Code 0 0 VCM + 0.25*VREF VCM − 0.25*VREF 11 1111 1111 0 0 VCM VCM 10 0000 0000 0 0 VCM − 0.25*VREF VCM + 0.25*VREF 00 0000 0000 0 1 VCM + 0.25*VREF VCM − 0.25*VREF 01 1111 1111 0 1 VCM VCM 00 0000 0000 0 1 VCM − 0.25*VREF VCM + 0.25*VREF 10 0000 0000 1 0 VCM + 0.5*VREF VCM − 0.5*VREF 11 1111 1111 1 0 VCM VCM 10 0000 0000 1 0 VCM − 0.5*VREF VCM + 0.5*VREF 00 0000 0000 1 1 VCM + 0.5*VREF VCM − 0.5*VREF 01 1111 1111 1 1 VCM VCM 00 0000 0000 1 1 VCM − 0.5*VREF VCM + 0.5*VREF 10 0000 0000 29 www.national.com ADC10D020 Applications Information ADC10D020 Applications Information 6.0 LAYOUT AND GROUNDING Proper routing of all signals and proper ground techniques are essential to ensure accurate conversion. Separate analog and digital ground planes may be used if adequate care is taken with signal routing, but may result in EMI/RFI. A single ground plane with proper component placement will yield good results while minimizing EMI/RFI. (Continued) 5.0 POWER SUPPLY CONSIDERATIONS A/D converters draw sufficient transient current to corrupt their own power supplies if not adequately bypassed. A 10 µF to 50 µF tantalum or aluminum electrolytic capacitor should be placed within half an inch (1.2 centimeters) of the A/D power pins, with a 0.1 µF ceramic chip capacitor placed as close as possible to each of the converter’s power supply pins. Leadless chip capacitors are preferred because they have low lead inductance. While a single voltage source should be used for the analog and digital supplies of the ADC10D020, these supply pins should be well isolated from each other to prevent any digital noise from being coupled to the analog power pins. A choke is recommended between the VA and VD supply lines. VDR should have a separate supply from VA and VD to avoid noise coupling. The VDR pins are completely isolated from the other supply pins. Because of this isolation, a separate supply can be used for these pins. This VDR supply can be significantly lower than the three volts used for the other supplies, easing the interface to lower voltage digital systems. Using a lower voltage for this supply can also reduce the power consumption and noise associated with the output drivers. The converter digital supply should not be the supply that is used for other digital circuitry on the board. It should be the same supply used for the ADC10D020 analog supply. As is the case with all high speed converters, the ADC10D020 should be assumed to have little high frequency power supply rejection. A clean analog power source should be used. No pin should ever have a voltage on it that is more than 300 mV in excess of the supply voltages or below ground, not even on a transient basis. This can be a problem upon application of power to a circuit and upon turn off of the power source. Be sure that the supplies to circuits driving the CLK, or any other digital or analog inputs do not come up any faster than does the voltage at the ADC10D020 power pins. Analog and digital ground current paths should not coincide with each other as the common impedance will cause digital noise to be added to analog signals. Accordingly, traces carrying digital signals should be kept as far away from traces carrying analog signals as is possible. Power should be routed with traces rather than the use of a power plane. The analog and digital power traces should be kept well away from each other. All power to the ADC10D020, except VDR, should be considered analog. The DR GND pin should be considered a digital ground and not be connected to the ground plane in close proximity with the other ground pins of the ADC10D020. Each bypass capacitor should be located as close to the appropriate converter pin as possible and connected to the pin and the appropriate ground plane with short traces. The analog input should be isolated from noisy signal traces to avoid coupling of spurious signals into the input. Any external component (e.g., a filter capacitor) connected between the converter’s input and ground should be connected to a very clean point in the ground return. The clock line should be properly terminated, as discussed in Section 3.1, and be as short as possible. Figure 8 gives an example of a suitable layout and bypass capacitor placement. All analog circuitry (input amplifiers, filters, reference components, etc.) and interconnections should be placed in an area reserved for analog circuitry. All digital circuitry and I/O lines should be placed in an area reserved for digital circuitry. Violating these rules can result in digital noise getting into the analog circuitry, which will degrade accuracy and dynamic performance (THD, SNR, SINAD). 20025575 FIGURE 8. An Acceptable Layout Pattern www.national.com 30 on even a transient basis can cause faulty or erratic operation. It is not uncommon for high speed digital circuits (e.g., 74F and 74AC devices) to exhibit overshoot and undershoot that goes a few hundred millivolts beyond the supply rails. A resistor of 50Ω to 100Ω in series with the offending digital input, close to the source, will usually eliminate the problem. Care should be taken not to overdrive the inputs of the ADC10D020 (or any device) with a device that is powered from supplies outside the range of the ADC10D020 supply. Such practice may lead to conversion inaccuracies and even to device damage. Attempting to drive a high capacitance digital data bus. The more capacitance the output drivers have to charge for each conversion, the more instantaneous digital current is required from VDR and DR GND. These large charging current spikes can couple into the analog section, degrading dynamic performance. Adequate bypassing and attention to board layout will reduce this problem. Buffering the digital data outputs (with a 74ACTQ841, for example) may be necessary if the data bus to be driven is heavily loaded. Dynamic performance can also be improved by adding series resistors of 47Ω to 56Ω at each digital output, close to the ADC output pins. Using a clock source with excessive jitter. This will cause the sampling interval to vary, causing excessive output noise and a reduction in SNR and SINAD performance. The use of simple gates with RC timing as a clock source is generally inadequate. Using the same voltage source for VD and external digital logic. As mentioned in Section 5.0, VD should use the same power source used by VA and other analog components, but should be decoupled from VA. (Continued) 7.0 DYNAMIC PERFORMANCE The ADC10D020 is ac tested and its dynamic performance is guaranteed. To meet the published specifications, the clock source driving the CLK input must be free of jitter. For best dynamic performance, isolating the ADC clock from any digital circuitry should be done with adequate buffers, as with a clock tree. See Figure 9. 20025576 FIGURE 9. Isolating the ADC Clock from Digital Circuitry 8.0 COMMON APPLICATION PITFALLS Driving the inputs (analog or digital) beyond the power supply rails. For proper operation, no input should go more than 300 mV beyond the supply pins. Exceeding these limits 31 www.national.com ADC10D020 Applications Information ADC10D020 Dual 10-Bit, 20 MSPS, 150 mW A/D Converter Physical Dimensions inches (millimeters) unless otherwise noted 48-Lead TQFP Package Ordering Number ADC10D020CIVS NS Package Number VBA48A NOTES UNLESS OTHERWISE SPECIFIED 1. STANDARD LEAD FINISH 7.62 MICROMETERS MINIMUM SOLDER PLATING (85/15) THICKNESS ON ALLOY 42/COPPER. 2. DIMENSION DOES NOT INCLUDE MOLD PROTRUSION. MAXIMUM ALLOWABLE MOLD PROTRUSION 0.15 mm PER SIDE. 3. REFERENCE JEDEC REGISTRATION MS-026, VARIATION ABC, DATED FEBRUARY 1999. LIFE SUPPORT POLICY NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. National Semiconductor Corporation Americas Email: [email protected] www.national.com National Semiconductor Europe Fax: +49 (0) 180-530 85 86 Email: [email protected] Deutsch Tel: +49 (0) 69 9508 6208 English Tel: +44 (0) 870 24 0 2171 Français Tel: +33 (0) 1 41 91 8790 2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. National Semiconductor Asia Pacific Customer Response Group Tel: 65-2544466 Fax: 65-2504466 Email: [email protected] National Semiconductor Japan Ltd. Tel: 81-3-5639-7560 Fax: 81-3-5639-7507 National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.