JAJSLI5J January 2011 – March 2021 OPA2835 , OPA835
PRODUCTION DATA
Figure 9-1 is an instrumentation amplifier that combines the high input impedance of the differential-to-differential amplifier circuit and the common-mode rejection of the differential-to-single-ended amplifier circuit. This circuit is often used in applications where high input impedance is required (such as taps from a differential line) or in cases where the signal source is a high impedance.
If VIN+ = VCM + VSIG+ and VIN– = VCM + VSIG–, the output of the amplifier may be calculated according to Equation 3.
The signal gain of the circuit is . VCM is rejected, and VREF provides a level shift around which the output signal swings. The single-ended output signal is in-phase with the differential input signal.
Integrated solutions are available, but the OPA835 device provides a much lower-power, high-frequency solution. For best CMRR performance, resistors must be matched. A good rule of thumb is CMRR ≈ the resistor tolerance; so 0.1% tolerance will provide approximately 60-dB CMRR.