Circuit Note CN-0251 Devices Connected/Referenced 4 R , 4-/8-Channel 15 V/+12 V/5 V ON ADG1409 iCMOS Multiplexer Low Cost, Wide Supply Range, Rail-to-Rail AD8226 Output, Instrumentation Amplifier Circuits from the Lab reference designs are engineered and Precision, Selectable Gain, Fully tested for quick and easy system integration to help solve todays AD8475 analog, mixed-signal, and RF design challenges. For more Differential Funnel Amplifier information and/or support, visit www.analog.com/CN0251. 4.8 kHz Ultralow Noise 24-Bit Sigma-Delta AD7192 ADC with PGA 50 mA, High Voltage, Micropower Linear ADP1720-5 5 V Regulator ADR444 Ultralow Noise, LDO XFET Voltage 24-Bit, 4.7 Hz, 4-Channel Analog Data Acquisition System A 10 V full-scale signal is very typical in process control and EVALUATION AND DESIGN SUPPORT industrial automation applications however, in some situations, Circuit Evaluation Boards the signal can be as small as several mV. Attenuation and level CN-0251 Circuit Evaluation Board (EVAL-CN0251-SDPZ) shifting is necessary to process a 10 V signal with modern low System Demonstration Platform (EVAL-SDP-CB1Z) voltage ADCs. However, amplification is needed for small signals Design and Integration Files Schematics, Layout Files, Bill of Materials to make use of the dynamic range of the ADC. Therefore, a circuit with a programmable gain function is desirable when the CIRCUIT FUNCTION AND BENEFITS input signal varies over a wide range. The circuit shown in Figure 1 is a flexible signal conditioning In addition, small signals may have large common-mode voltage circuit for processing signals of wide dynamic range, varying swings therefore, high common-mode rejection (CMR) is required. from several mV p-p to 20 V p-p. The circuit provides the In some applications, where the source impedance is large, high necessary conditioning and level shifting and achieves the impedance is also necessary for the analog front-end input circuit. dynamic range using the internal programmable gain amplifier (PGA) of the high resolution analog-to-digital converter (ADC). +15VA +15VA ADP1720 ADR444 330H 100MHz +5VA A4V096 V V IN OUT +5VA IN OUT A4V096 10F D3V3 GND GND 1F DGND AGND D3V3 +5VA 0.1F DGND 0.1F 0.1F D3V3 +15VA 0.1F +15VA DGND 3 *OMIT R FOR G = 1 V G DD 18 20 21 19 15 16 IN 0.4x +V S 7 NC 2 AGND AV DV DGND 1k DD DD 100k ADG1409 10nF VN 1.25k VS1A S1A 1nF 1.25k +V OUT 100 AV S IN 0.8x AIN2 0.1F DD 12 DA 1 5 8 AIN1 VOCM 1F VOCM VP 11 IN VS4A 4 1 AD8226 AD8475 S4A 4.02k DOUT/RDY AIN3 1.25k 100 13 23 DOUT +IN 0.8x R * R G G SERIAL 10 6 AIN4 2 V DIN OUT 14 +OUT INTERFACE 24 DIN - AINCOM 10nF IA 7 PGA 1.25k 1k 10nF AND 10 ADC SCLK 3 SCLK 3 CONTROL 6 VS1B +IN 0.4x R S1B G LOGIC CS 9 REF V AD8475 4 CS S DB 4 +IN 8 SYNC 5 AD7192 SYNC 25 VS4B S4B 4.02k V S AGND P3 TEMP 5 P3 1nF 0.1F SENSOR BPDSW P2 6 P2 17 15VA 1-OF-4 CLOCK DECODER CIRCUITRY V GND A0 A1 EN SS NC AGND 91 2 7 8 MCLK1 MCLK2 15VA Figure 1. Flexible Analog Front-End Circuit for Wide Industrial Range Signal Conditioning Rev. B 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 One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. determining its suitability and applicability for your use and application. Accordingly, in no event shall Tel: 781.329.4700 www.analog.com Analog Devices be liable for direct, indirect, special, incidental, consequential or punitive damages due Fax: 781.461.3113 20122013 Analog Devices, Inc. All rights reserved. to any cause whatsoever connected to the use of any Circuits from the Lab circuits. (Continued on last page) MUX REFIN1(+) REFIN1() P0/REFIN2() P1/REFIN2(+) 10351-001CN-0251 Circuit Note The circuit shown in Figure 1 solves all of these challenges device that is particularly suitable for high resolution, - ADCs and provides programmable gain, high CMR, and high input and precision data acquisition systems. impedance. The input signal passes through the 4-channel Input Switch and Protection ADG1409 multiplexer into the AD8226 low cost, wide input The ADG1409 multiplexer has 2-bit binary address lines that range instrumentation amplifier. The AD8226 offers high CMR are used to select one of four possible input channels. The design up to 80 dB and very high input impedance (800 M differential also includes external protection such as standard diodes and mode and 400 M common mode). A wide input range and transient voltage suppressors to enhance the robustness of the rail-to-rail output allow the AD8226 to make full use of the circuit. These are not shown in Figure 1 however, they are shown supply rails. in the detailed schematics and other documentation in the The AD8475 is a fully differential, attenuating amplifier with CN0251 Design Support Package. integrated precision gain resistors. It provides precision attenuation The ADG1409 multiplexer is configured to accept four (G = 0.4 or G = 0.8), common-mode level shifting, and single- differential input signals: (VS1A VS1B), (VS2A VS2B), ended-to-differential conversion. The AD8475 is an easy to use, (VS3A VS3B), and (VS4A VS4B). The outputs of the fully integrated precision gain block, designed to process signal multiplexer, DA and DB, are applied to the inputs of the levels up to 10 V on a single supply. Therefore, the AD8475 is AD8226 in-amp. suitable for attenuating signals from the AD8226 up to 20 V p-p, AD8226 Input Instrumentation Amplifier while maintaining high CMR and offering a differential output to drive the differential input ADC. The external RG resistor sets the gain of the AD8226. For this circuit, RG is omitted, and the gain of the in-amp stage is 1. The The AD7192 is a 24-bit sigma-delta (-) ADC with an internal output of the AD8226 is therefore VSxA VSxB, where x is the PGA. The on-chip, low noise gain stage (G = 1, 8, 16, 32, 64, or input channel number. 128) means that signals of large and small amplitude can be interfaced directly to the ADC. The differential input of the AD8226 is filtered by two 4.02 k resistors and a 10 nF capacitor, which form a single-pole RC filter With the combination of the previous parts, the circuit offers with a cutoff frequency of 2.0 kHz. The two 1 nF capacitors add very good performance and easy configuration for signals common-mode filtering with a cutoff frequency of 40 kHz. with varying amplitudes. The circuit can be used in industrial automation, process control, instrumentation, and medical AD7192 ADC PGA Gain Configuration equipment applications. The AD7192 is configured to accept differential analog inputs CIRCUIT DESCRIPTION to match the differential output signals from the AD8475. The full-scale input range of the AD7192 is V /gain, where REF The circuit comprises of an ADG1409 multiplexer, an AD8226 VREF = REFINx(+) REFINx(). instrumentation amplifier, an AD8475 difference amplifier, and an AD7192 - ADC with an ADR444 reference, and the ADP1720 When the buffer in the AD7192 is enabled, the input channel regulator. Only a few external components are used for protection, drives the high impedance input stage of the buffer amplifier, and filtering, and decoupling, making this circuit highly integrated, and the absolute input voltage range in this mode is restricted to a it requires a small circuit board (printed circuit board PCB ) area. range of AGND + 250 mV and AV 250 mV. When the gain DD stage is enabled, the output from the buffer is applied to the input Regulator and Reference Selection of the PGA, and the analog input range must be limited to The ADP1720-5 was chosen as the 5 V regulator for this circuit. (AV 1.25 V)/gain because the PGA requires additional DD It is a high voltage micropower, low dropout linear regulator headroom. Therefore, with a 4.096 V reference and a 5 V power suitable for industrial applications. supply, and to make the maximum use of the dynamic range of the The 4.096 V ADR444 reference was chosen as the reference for ADC, the signal can be attenuated or amplified as shown in Table 1. this circuit. It is an ultralow noise, high accuracy, low dropout Table 1. Gain Configurations for the AD8475 and the AD7192 Internal PGA for Various Input Ranges Input Range (VSxA VSxB) Gain of AD8475 Gain of AD7192 PGA Output Range, Bipolar Mode (V) 10 V 0.4 1 4 5 V 0.8 1 4 1 V 0.4 8 3.2 500 mV 0.8 8 3.2 250 mV 0.8 16 3.2 125 mV 0.8 32 3.2 62.5 mV 0.8 64 3.2 31.25 mV 0.8 128 3.2 Rev. B Page 2 of 6