Programmable gain amplifier circuit composed of the AD7523

Published:2011/5/5 19:21:00 Author:TaoXi | Keyword: Programmable, gain amplifier | From:SeekIC

The programmable gain amplifier circuit can amplifies, transforms and filter the analog signal, and interconnects the multiple function-modules of the device, and reconstructs the circuit, also it can adjust the circuit's gain, bandwidth, and threshold. The programmable gain amplifier circuit composed of the AD7523 is as shown in the figure. The circuit's gain is controlled by the 8-bit data to ensure the gain is between 1 to 256, as from the D7 (MSB) there is only one high-level voltage, so it is able to make 6dB as the step length, from 6dB to 42 dB. The AD7523 has the analog switch and R-2R ladder network, the rated resistance is 5～20kΩ, the center value is 10kΩ. If you input the signal from RFB port, the side input resistance will be low, so we connect the buffer amplifier Al before the RFB port as the inverter. If you input from the Al's same-phase port, you can get the same-phase signal. For the variable gain amplifier, if the gain is high, the imbalance voltage is high, so you need to adjust the Op amp to zero and particular pay attention to the output of Al. We usually do the gain calibration on the RFB port series potentiometer RP2. The set gain of op amp A2 is higher, the closed-loop frequency response is worser because the negative feedback of op amp A2 can be changed. We need to use the op amp with narrow gain variable range or good open-loop frequency feature. For small power or accurate op amp, the AC characteristics are sacrificed, so we should pay more attention when we input the signal of thousands Hz.



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