Complete High Speed, High CMRR Precision Analog Front End for Process Control (CN0213)

Signal levels in industrial process control systems generally fall into one of the following categories: single-ended current (4 mA-to-20 mA), single-ended, differential voltage (0 V to 5V, 0 V to 10 V, ±5 V, ±10 V), or small signal inputs from sensors such as thermocouples or load cells. Large common-mode voltage swings are also typical, especially for small signal differential inputs; therefore good common-mode rejection is an important specification in the analog signal processing system.


The analog front-end circuit shown in Figure 1 is optimized for high precision and high common-mode rejection ratio (CMRR) when processing these types of industrial-level signals.



Figure 1. High Performance Analog Front End for Process Control (Simplified Schematic: All Connections and Decoupling Not Shown)


The circuit level shifts and attenuates the signals so they are compatible with the input range requirements of most modern single-supply SAR ADCs, such as the AD7685 high performance 16-bit 250 kSPS PulSAR® ADC.


With an 18 V p-p input signal, the circuit achieves approximately 105 dB common-mode rejection (CMR) at 100 Hz and 80 dB CMR at 5 kHz.


High precision, high input impedance, and high CMR are provided by the AD8226 instrumentation amplifier. For high precision applications, a high input impedance is required to minimize system gain errors and also to achieve good CMR. The AD8226 gain is resistor-programmable from 1 to 1000.


A resistive level shifter/attenuator stage directly on the input would inevitably degrade CMR performance due to the mismatch between the resistors. The AD8226 provides the excellent CMR required for both small signal and large signal inputs. The AD8275 level shifter/attenuator/driver performs the attenuation and level shifting function in the circuit, without any need for external components.


Traditionally, sigma-delta ADCs have been used in high resolution measurement systems because signal bandwidths are quite low, and the sigma-delta architecture provides excellent noise performance at low update rates. However, there is an increased trend for higher update rates, especially in multichannel systems, to allow faster per-channel update, or for increased channel density. In such cases a high performance SAR ADC is a good alternative. The circuit shown in Figure 1 uses the AD7685 250 kSPS 16 bit ADC, with the AD8226 high performance in-amp, and the AD8275 attenuator/level shifter amplifier implemented as a complete system solution without the need for any external components.

Файлы

Используемые компоненты

Производитель: Analog Devices Inc.
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AD8226ARMZ
AD8226ARMZ
Analog Devices Inc.
Арт.: 439275 ИНФО PDF RD
Доступно: 11053 шт. от: 148 руб.
LS: Wide Supply Range. Rail-to-Rail Output Instrumentation Amplifier
AD8226ARMZ 148,00 от 23 шт. 127,00 от 50 шт. 116,00
1945 шт.
(на складе)
9108 шт.
(под заказ)
AD8226ARZ
AD8226ARZ
Analog Devices Inc.
Арт.: 563305 PDF RD
Доступно: 7093 шт. от: 150 руб.
IC, AMP, INST, R-R, LP, 13MA, 8SO
AD8226ARZ 150,00 от 23 шт. 129,00 от 49 шт. 118,00
2557 шт.
(на складе)
4536 шт.
(под заказ)
AD8226BRMZ
AD8226BRMZ
Analog Devices Inc.
Арт.: 568125 PDF RD
Доступно: 7771 шт.
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INSTR AMP, 1.5MHZ, 120DB, MSOP-8
AD8226BRMZ
7771 шт.
(под заказ)
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ADR439ARM
Analog Devices Inc.
Арт.: 600242 ИНФО RD
Доступно: 1858 шт.
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IC VREF PREC 4.5V 30MA 8-MSOP
ADR439ARM
1858 шт.
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AD8226ARMZ-R7
AD8226ARMZ-R7
Analog Devices Inc.
Арт.: 1074386 PDF RD
Доступно: 46641 шт.
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AMPLIFIER, INSTRUMENTATION, 1.5MHZ, 80dB, MSOP-8, FULL REEL
AD8226ARMZ-R7
46641 шт.
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AD8226ARZ-R7
Analog Devices Inc.
Арт.: 1074455 ИНФО RD
Доступно: 12150 шт.
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IC AMP INST R-R LP 13MA 8SOIC
AD8226ARZ-R7
12150 шт.
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AD8226BRMZ-R7
Analog Devices Inc.
Арт.: 1198712 ИНФО RD
Доступно: 18586 шт.
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IC INSTR AMP +/-18 8MSOP
AD8226BRMZ-R7
18586 шт.
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AD8226BRZ
AD8226BRZ
Analog Devices Inc.
Арт.: 1640221 PDF RD
Доступно: 1863 шт.
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INSTR AMP, 1.5MHZ, 120DB, NSOIC-8
AD8226BRZ
1863 шт.
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AD8226ARZ-RL
Analog Devices Inc.
Арт.: 2258313 ИНФО RD
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IC AMP INST R-R LP 13MA 8SOIC
AD8226ARZ-RL
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