Circuit Note CN-0277 Devices Connected/Referenced Circuits from the Lab® reference designs are engineered and tested for quick and easy system integration to help solve today’s analog, mixed-signal, and RF design challenges. For more information and/or support, visit www.analog.com/CN0277. AD7960 18-Bit, 5 MSPS PulSAR® Differential ADC ADA4897-1/ ADA4897-2 1 nV/√Hz, Low Power, Rail-to-Rail Output Single/Dual Amplifiers AD8031/ AD8032 2.7 V, 800 μA, 80 MHz Rail-to-Rail I/O Single/Dual Amplifiers ADR4550 Ultralow Noise, High Accuracy Voltage References 18-Bit, 5 MSPS, Data Acquisition System Optimized for AC Performance EVALUATION AND DESIGN SUPPORT CIRCUIT FUNCTION AND BENEFITS Circuit Evaluation Boards AD7960 Circuit Evaluation Board (EVAL-AD7960FMCZ) System Demonstration Platform (EVAL-SDP-CH1Z) Design and Integration Files Schematics, Layout Files, Bill of Materials The circuit shown in Figure 1 is an 18-bit, 5 MSPS low power, low noise, high-precision complete data acquisition signalchain solution that dissipates only 122 mW. The reference, reference buffer, driver amplifiers, and ADC provide an optimized solution with industry-leading SNR of 99 dB, THD of −117 dB. The circuit is ideal for portable applications because of its low power and small PCB footprint. +7V +5V +7V +5V AD8031 ADR4550 +VS +7V/+5V/EXT 0.1µF VIN+ +5V +1.8V VCM = VREF ÷ 2 = 2.5V 820Ω 33Ω 100pF 56pF 1kΩ 0.1µF VREF = 5V REFIN REF VDD1 VDD2 VIO ADA4897-1 0.1µF CNV+/ CNV– 100Ω VIN+ VCM = 2.5V IN+ –2.5V/EXT –VS VIN– GND VIN– VCM = VREF ÷ 2 = 2.5V 820Ω IN– 33Ω GND 100pF 1kΩ 0.1µF 56pF ADA4897-1 0.1µF 100Ω DCO+/DCO– 100Ω AD7960 +VS +7V/+5V/EXT 0.1µF D+/D– VCM CLK+/CLK– 100Ω +2.5V +7V AD8031 10798-001 –2.5V/EXT –VS Figure 1. 18-Bit, 5 MSPS Signal Chain (All Connections and Decoupling Not Shown) Rev. C Circuits from the Lab® reference designs from Analog Devices have been designed and built by Analog Devices engineers. Standard engineering practices have been employed in the design and construction of each circuit, and their function and performance have been tested and verified in a lab environment at room temperature. However, you are solely responsible for testing the circuit and determining its suitability and applicability for your use and application. Accordingly, in no event shall Analog Devices be liable for direct, indirect, special, incidental, consequential or punitive damages due toanycausewhatsoeverconnectedtotheuseofanyCircuitsfromtheLabcircuits. (Continuedonlastpage) One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 www.analog.com Fax: 781.461.3113 ©2013–2014 Analog Devices, Inc. All rights reserved. CN-0277 Circuit Note 1.00 The circuit uses supplies of +7 V and −2.5 V for the input ADA4897-1 drivers to minimize power dissipation and to achieve the optimum system distortion performance. The ADA4897-1 output stage is rail-to-rail and swings to within 150 mV of each supply rail. The additional headroom afforded by the +7 V and −2.5 V supplies provides excellent distortion performance. INL (LSB) 0 –0.25 –0.50 –1.00 0 50000 100000 150000 200000 250000 CODE 10798-002 –0.75 Figure 2. AD7960 Typical Integral Nonlinearity vs. Output Code, REF = 5 V Histogram and FFT Performance The precision performance of the circuit shown in the histogram plot in Figure 3 and the FFT plot in Figure 4 using a 5 V external reference . The data was taken using the EVAL-AD7960FMCZ evaluation board and the Audio Precision SYS-2702 as a signal source. Figure 3. Typical Histogram, REF = 5 V Rev. C | Page 2 of 5 260000 240000 10798-003 BINS 220000 200000 180000 160000 140000 120000 100000 110,000 105,000 100,000 95,000 90,000 85,000 80,000 75,000 70,000 65,000 60,000 55,000 50,000 45,000 40,000 35,000 30,000 0 The AD7960, 5MSPS, 18-bit converter has ±0.8 LSB INL, ±0.5 LSB DNL, 100 dB DR, and dissipates only 46.5 mW. As shown in Figure 1, the AD7960 is powered from +5 V (VDD1) and +1.8 V (VDD2 and VIO) supplies. The required 5 V and 1.8 V supplies can be generated using LDOs such as ADP7104 and ADP124. 0.25 80000 The AD7960 digital interface uses low voltage differential signaling (LVDS) to enable high data transfer rates. An LVDS CLK+/CLK− signal must be applied to the AD7960 to transfer data to the digital host. 0.50 OCCURRENCES The AD7960 differential input range is set by a 5 V or 4.096 V external reference voltage. In Figure 1, the 5 V reference is supplied by the ADR4550 is a high precision, low power (max 950 µA operating current), low noise voltage reference featuring ±0.02% maximum initial error, excellent temperature stability, and low output noise. The AD8031 is used to buffer the external reference and the common-mode output voltage of the AD7960, and is an ideal for a wide range of applications, from battery-operated systems with large bandwidth to high-speed systems where component density requires lower power dissipation. The AD8031 is also stable for large capacitive loads, and can drive the decoupling capacitors that are required to minimize voltage spikes caused by transient currents. 0.75 60000 The input signals to the ADA4897-1 op amps are filtered by the 820 Ω/ 100 pF network that has a bandwidth of 2 MHz. Additional filtering at the input of the AD7960 ADC is provided by the 33 Ω/ 56 pF network that has a bandwidth of 86 MHz. The latter filter helps to reduce the kick back coming from the cap DAC input of the AD7960 and limits the noise coming to the AD7960 inputs. 40000 The ADA4897-1 is an ideal candidate for driving the AD7960 high precision 18-bit, 5 MSPS SAR ADC. The ADA4897-1 is a low noise (1 nV/√Hz typical) and low power (3 mA) rail-to-rail output amplifier that has 230 MHz bandwidth, 120 V/μs slew rate, and settles to 0.1% in 45 ns. The AD7960 converts the differential voltage of the antiphase analog inputs (IN+ and IN−) into a digital output. The analog inputs, IN+ and IN−, require a common-mode voltage equal to one-half the reference voltage. The low noise and low power AD8031 amplifier buffers the +5V reference voltage from the low noise and low drift ADR4550 and it also buffers the commonmode output voltage (VCM) of the AD7960. The ADA4897-1 is configured as a unity gain buffer and drives the inputs of the AD7960 with a 0 V to 5 V differential anti-phase (180°out of phase with each other). Figure 2 shows the typical integral nonlinearity as a function of the AD7960 output code is within the specifications of ±0.8 LSB using a 5 V external reference. 20000 CIRCUIT DESCRIPTION Circuit Note CN-0277 CIRCUIT EVALUATION AND TEST 0 REFERENCE = 5V INPUT FREQENCY = 1kHz SNR = 96.5dB SINAD = 96dB THD = –111.5dB SFDR = 113.1dB –20 AMPLITUDE (dB) –40 The EVAL-AD7960FMCZ evaluation board was developed to evaluate and test the AD7960 ADC. To test the circuit shown in Figure 1, two ADA4897-1 op amps were used to drive the AD7960. –60 A detailed schematic and user instructions are available in the EVAL-AD7960FMCZ user guide UG-490. This documentation describes how to run the ac/dc tests described in this circuit note. –80 –100 –120 Note that the user has the option to provide +7 V and −2.5 V supplies for the input amplifiers on the EVAL-AD7960FMCZ board from the external dual power supply. –140 –160 0 0.5 1.0 1.5 2.0 FREQUENCY (MHz) 2.5 A functional block diagram of the test setup is shown in Figure 5, and a photograph of the evaluation board is shown in Figure 6 10798-004 –180 Equipment Required Figure 4. 1 kHz, −0.5 dBFS Input Tone FFT, REF = 5 V Complete schematics and layout of the printed circuit board can be found in the CN-0277 Design Support Package: www.analog.com/CN0277-DesignSupport . The following equipment is required to test the circuit: COMMON VARIATIONS The AD7961 is a 16-bit, 5 MSPS PulSAR® differential ADC and is pin compatible with the AD7960 PulSAR® family, so it can be used in place of the AD7960 in the circuit of Figure 1 when only 16-bit performance is required. The AD7960 series supports either 4.096 V or 5 V external references. The EVAL-AD7960FMCZ board allows either the ADR4540 (4.096 V) or the ADR4550 (5 V) to be selected with a jumper. The various options for connecting the reference voltage are controlled by the enable EN[0:3] pins of the AD7960 as described in the AD7960 datasheet. If a 0 V to 5 V input range is required, the ADR4550 reference can be used with the AD8031 reference buffer. This is done by setting the enable pins of the AD7960 as EN[0:3] = ‘X001’ or ‘X101’. The ADA4897-1 and AD8031 single op amps can be replaced with their dual versions (ADA4897-2 and AD8032, respectively) if desired. For optimized noise and distortion performance, the ADA4899-1 (15 mA), unity-gain stable, ultralow distortion, 1 nV/√Hz voltage noise, high speed op amp can be used instead of the ADA4897-1 in the circuit if desired. Rev. C | Page 3 of 5 • The EVAL-AD7960FMCZ Evaluation Board and Software • The System Demonstration Platform (EVAL-SDPCH1Z) board • A low distortion signal generator, such as the Agilent 81150A or Audio Precision SYS2702 • A PC with a USB 2.0 port running Windows® XP, Windows Vista, or Windows 7 (32-bit or 64-bit) • A 12 V dc wall wart (included with EVAL-SDP-CH1Z board) • USB interface Cable (1) and SMA cable (1) CN-0277 Circuit Note +12V WALL WART ADP7102 +5V ADP7104 +12V ADP2300 +12V +7V PC (USB) USB PORT –VS = –2.5V ADR4550 +7V POWER SUPPLY CIRCUITRY ADP124 +5V +5V AD8031 +1.8V +VS REFIN AIN+ REF VDD1 VDD2 VIO CNV± 100Ω AD4897-1 ADSP-BF522 –VS IN+ D± 100Ω AD7960 SIGNAL GENERATOR +7V AUDIO PRECISION SYS-2702 GND AD4897-1 AIN– LVDS INTERFACE DCO± IN– –VS VCM SPARTAN-6 FPGA XC6SLX25 100Ω CLK± 100Ω 2.5V +7V VCM AD8031 EVAL-SDP-CH1Z 10798-005 EVAL-AD7960FMCZ 160-PIN 10mm VITA 57 CONNECTOR Figure 5. Functional Diagram of Test Setup TO +12V WALL WART SMA CONNECTOR USB PC 10798-006 SIGNAL SOURCE Figure 6. EVAL-AD7960FMCZ Board Connected to EVAL-SDP-CH1Z Board Rev. C | Page 4 of 5 Circuit Note CN-0277 REVISION HISTORY LEARN MORE 2/14—Rev. B to Rev. C CN-0277 Design Support Package: www.analog.com/CN0277-DesignSupport CN-0307 Circuit Note, CN-0307 Circuit Note, A 16-Bit, 6 MSPS SAR ADC System with Low Power Input Drivers and Reference Optimized for Multiplexed Applications Changes to Common Variations Section ....................................... 3 Changes to Learn More Section ...................................................... 5 12/13—Rev. A to Rev. B Changes to Title ................................................................................. 1 CN-0237 Circuit Note, Ultralow Power, 18-Bit, Differential PulSAR® ADC Driver. 9/13—Rev. 0 to Rev. A MT-031 Tutorial, Grounding Data Converters and Solving the Mystery of AGND and DGND. Analog Devices. 8/13—Revision 0: Initial Version Changes to Figure 3 .......................................................................... 2 MT-035 Tutorial, Op Amp Inputs, Outputs, Single-Supply, and Rail-to-Rail Issues. Analog Devices. MT-101 Tutorial, Decoupling Techniques. Analog Devices. Voltage Reference Wizard Design Tool. UG-490 User Guide, Evaluating the AD7960 18-Bit, 5 MSPS PulSAR Differential ADC, Analog Devices. UG-502 User Guide, SDP-H1 Controller Board, Analog Devices. Data Sheets and Evaluation Boards AD7960 Data Sheet and Evaluation Board ADA4897-1 Data Sheet ADA4897-2 Data Sheet ADR4550 Data Sheet AD8031 Data Sheet AD8032 Data Sheet (Continued from first page) Circuits from the Lab reference designs are intended only for use with Analog Devices products and are the intellectual property of Analog Devices or its licensors. While you may use the Circuits from the Lab reference designs in the design of your product, no other license is granted by implication or otherwise under any patents or other intellectual property by application or use of the Circuits from the Lab reference designs. Information furnished by Analog Devices is believed to be accurate and reliable. However, Circuits from the Lab reference designs are supplied "as is" and without warranties of any kind, express, implied, or statutory including, but not limited to, any implied warranty of merchantability, noninfringement or fitness for a particular purpose and no responsibility is assumed by Analog Devices for their use, nor for any infringements of patents or other rights of third parties that may result from their use. Analog Devices reserves the right to change any Circuits from the Lab reference designs at any time without notice but is under no obligation to do so. ©2013–2014 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. CN10798-0-2/14(C) Rev. C | Page 5 of 5