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ADC10321

10-Bit, 20MSPS, 98mW A/D Converter with Internal

Sample and Hold

General Description

The ADC10321 is a low power, high performance CMOS

analog-to-digital converter that digitizes signals to 10 bits

resolution at sampling rates up to 25Msps while consuming

a typical 98mW from a single 5V supply. Reference force

and sense pins allow the user to connect an external refer-

ence buffer amplifier to ensure optimal accuracy. No missing

codes is guaranteed over the full operating temperature

range. The unique two stage architecture achieves 9.2 Ef-

fective Bits with a 10MHz input signal and a 20MHz clock

frequency. Output formatting is straight binary coding.

To ease interfacing to 3V systems, the digital I/O power pins

of the ADC10321 can be tied to a 3V power source, making

the outputs 3V compatible. When not converting, power

consumption can be reduced by pulling the PD (Power

Down) pin high, placing the converter into a low power

standby state, where it typically consumes less than 4mW.

The ADC10321’s speed, resolution and single supply opera-

tion makes it well suited for a variety of applications in video,

imaging, communications, multimedia and high speed data

acquisition. Low power, single supply operation ideally suit

the ADC10321 for high speed portable applications, and its

speed and resolution are ideal for charge coupled device

(CCD) input systems.

The ADC10321 comes in a space saving 32-pin TQFP and

operates over the industrial (−40˚C ≤ T

≤ +85˚C) tempera-

ture range.

Features

n Internal Sample-and-Hold

n Single +5V Operation

n Low Power Standby Mode

n Guaranteed No Missing Codes

n Tri-State Outputs

n TTL/CMOS or 3V Logic Input/Output Compatible

Key Specifications

n Resolution 10 Bits

n Conversion Rate 20 Msps

n ENOB

10MHz Input 9.2 Bits (typ)

n DNL 0.35 LSB (typ)

n Conversion Latency 2 Clock Cycles

n PSRR 56dB

n Power Consumption 98mW (typ)

n Low Power Standby Mode

4mW (typ)

Applications

n Digital Video

n Communications

n Document Scanners

n Medical Imaging

n Electro-Optics

n Plain Paper Copiers

n CCD Imaging

January 2003

ADC10321 10-Bit, 20MSPS, 98mW A/D Converter with Internal Sample and Hold

Summary of content (18 pages)

PAGE 1
ADC10321 10-Bit, 20MSPS, 98mW A/D Converter with Internal Sample and Hold General Description The ADC10321 is a low power, high performance CMOS analog-to-digital converter that digitizes signals to 10 bits resolution at sampling rates up to 25Msps while consuming a typical 98mW from a single 5V supply. Reference force and sense pins allow the user to connect an external reference buffer amplifier to ensure optimal accuracy. No missing codes is guaranteed over the full operating temperature range.
PAGE 2
ADC10321 Connection Diagram 10089701 Ordering Information Commercial (−40˚C ≤ TA ≤ +85˚C) NS Package ADC10321CIVT TQFP Block Diagram 10089702 www.national.
PAGE 3
ADC10321 Pin Descriptions and Equivalent Circuits Pin No. Symbol Description Equivalent Circuit Analog I/O 30 VIN Analog Input signal to be converted. Conversion range is VREF+ S to VREF− S. 31 VREF+ F Analog input that goes to the high side of the reference ladder of the ADC. This voltage should force VREF+ S to be in the range of 2.3V to 4.0V. 32 VREF+ S Analog output used to sense the voltage near the top of the ADC reference ladder.
PAGE 4
ADC10321 Pin Descriptions and Equivalent Circuits Pin No. Symbol 5, 10 (Continued) Description Equivalent Circuit Positive digital supply pins. These pins should be connected to a clean, quiet voltage source of +5V. VA and VD should have a common supply and be separately bypassed with 10µF to 50µF capacitors in parallel with 0.1µF capacitors. VD 12, 21 VD I/O Positive supply pins for the digital output drivers.
PAGE 5
Machine Model (Notes 1, 200V 2) Soldering Temp., Infrared, 10 sec. (Note 6) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Storage Temperature Positive Supply Voltage (V = VA = VD) Voltage on Any I/O Pin Operating Ratings(Notes 1, 2) 6.5V Operating Temperature −0.3V to (VA or VD) +0.3V) Package Input Current (Note 3) Package Dissipation at TA = 25˚C +4.5V to +5.
PAGE 6
ADC10321 Converter Electrical Characteristics (Continued) The following specifications apply for VA = +5.0VDC, VD = 5.0VDC, VD I/O = 5.0VDC, VREF+ = +3.5VDC, VREF− = +1.5VDC, CL = 20pF, fCLK = 20MHz, RS = 25Ω.
PAGE 7
(Continued) The following specifications apply for VA = +5.0VDC, VD I/O = 5.0VDC, VREF+ = +3.5VDC, VREF− = +1.5VDC, fCLK = 20MHz, trc = tfc = 5ns, RS = 25Ω.
PAGE 8
ADC10321 AC Electrical Characteristics (Continued) 10089712 10089724 10089711 Note 8: Typical figures are at TA = TJ = 25˚C, and represent most likely parametric norms. Note 9: Tested limits are guaranteed to Nationsl’s AOQL (Average Outgoing Quality Level). Note 10: When the input signal is between VREF+ and (VA + 300mV), the output code will be 3FFh, or all 1s. When the input signal is between −300 mV and VREF−, the output code will be 000h, or all 0s.
PAGE 9
SINAD & ENOB vs VA SINAD & ENOB vs fCLK and fIN 10089732 10089731 IA + ID vs. Temperature 10089737 Spectral Response at 20 MSPs 10089735 9 www.national.com ADC10321 Typical Performance Characteristics VA = VD = VDI/O = 5V, fCLK = 20MHz, unless otherwise specified.
PAGE 10
ADC10321 OUTPUT DELAY is the time delay after the fall of the input clock before the data update is present at the output pins. OUTPUT HOLD TIME is the length of time that the output data is valid after the fall of the input clock. OVER RANGE RECOVERY TIME is the time required after VIN goes from AGND to VREF+ or VIN goes from VA to VREF− for the converter to recover and make a conversion with its rated accuracy.
PAGE 11
ADC10321 Timing Diagram 10089715 FIGURE 1. ADC10321 Timing Diagram 10089717 10089716 FIGURE 2. AC Test Circuit FIGURE 3. tEN, tDIS Test Circuit 11 www.national.
PAGE 12
ADC10321 bandwidth, low distortion and minimal Differential Gain and Differential Phase. The LMH6702 performs best with a feedback resistor of about 100 ohms. Care should be taken to keep digital noise out of the analog input circuitry to maintain highest noise performance. Functional Description The ADC10321 maintains excellent dynamic performance for input signals up to half the clock frequency.
PAGE 13
ADC10321 Applications Information (Continued) 10089718 FIGURE 4. Simple, low component count reference biasing 13 www.national.
PAGE 14
ADC10321 Applications Information (Continued) 10089719 FIGURE 5. Better low component count reference biasing Voltages at the reference sense pins (VREF+ S and VREF− S) should be within the range specified in the Operating Ratings table (2.3V to 4.0V for VREF+ and 1.3V to 3.0V for VREF−). Any device used to drive the reference pins should be able to source sufficient current into the VREF+ F pin and sink sufficient current from the VREF− F pin when the ladder is at its minimum value of 850 Ohms.
PAGE 15
ADC10321 Applications Information (Continued) 10089720 FIGURE 6. Setting precision reference voltages 3.0 POWER SUPPLY CONSIDERATIONS A/D converters draw sufficient transient current to corrupt their own power supplies if not adequately bypassed. A 10µF to 50µF tantalum or aluminum electrolytic capacitor should be placed within an inch (2.5 centimeters) of the A/D power pins, with a 0.1µF ceramic chip capacitor placed as close as possible to each of the converter’s power supply pins.
PAGE 16
ADC10321 Applications Information 5.0 LAYOUT AND GROUNDING (Continued) Proper routing of all signals and proper ground techniques are essential to ensure accurate conversion. Separate analog and digital ground planes are required to meet data sheet limits. The analog ground plane should be low impedance and free of noise form other parts of the system. The clock line should be series terminated at the source end in the characteristic impedance of that line.
PAGE 17
operation. It is not uncommon for high speed digital circuits (e.g., 74F and 74AC devices) to exhibit undershoot that goes more than a volt below ground. A resistor of 50 to 100Ω in series with the offending digital input will usually eliminate the problem. Care should be taken not to overdrive the inputs of the ADC10321 (or any device) with a device that is powered from supplies outside the range of the ADC10321 supply. Such practice may lead to conversion inaccuracies and even to device damage.
PAGE 18
ADC10321 10-Bit, 20MSPS, 98mW A/D Converter with Internal Sample and Hold Physical Dimensions inches (millimeters) unless otherwise noted 32-Lead TQFP Package Ordering Number ADC10321CIVT NS Package Number VBE32A 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.