How does the potentiometer achieve multiple gains of the in-phase amplifier

Considering the resistance matching: RF1 / RG1 = RF2 / RG2 = 1, so the output current I0 can be simplified to Vref / R1. Although the circuit is a high-precision current source, there will still be resistance matching errors, AD8276 A and B gain errors, and the voltage divider R1 and load resistance tolerances. Therefore, precise resistors are still required to achieve a precise current source. If a larger error is acceptable, the AD8603 can be removed, and pin 1 of the AD8276 is directly connected to the Vload node.

Digital potentiometer, also known as NC programmable resistor, is a new type of integrated circuit for CMOS digital and analog mixed signal processing that replaces traditional mechanical potentiometer (analog potentiometer). The digital potentiometer is controlled by a digital input and produces an analog output.

Depending on the digital potentiometer, the maximum tap current can be from a few hundred microamperes to a few milliamperes. The digital potentiometer uses numerical control to adjust the resistance value. It has the characteristics of flexible use, high adjustment accuracy, no contact, and low noise. It can replace the mechanical potentiometer in many fields.

The non-inverting amplifier is another basic operational amplifier circuit, which uses negative feedback to stabilize the total voltage gain. The negative feedback of this amplifier can also increase the input impedance and reduce the output impedance.

A variable gain non-inverting amplifier composed of a digital potentiometer (AD5270 / AD5272) and an operational amplifier (AD8615) is used.

How to calculate the maximum circuit gain?

When the input signal is alternating current, the parasitic capacitance of the digital potentiometer will have a greater impact and may oscillate at the output. What is the solution to this situation?

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