# Differential Amplifier Resistor Tolerance Analysis

Make all resistors “Control Objects” and use “Parameter Stepping” to step each resistor value from 9.9k (1% low) to 10.1k (1% high) in 3 linear steps. Run DC Analysis, “DC Transfer Characteristic” and sweep “Vcmv” from -1V to +1V. The resulting family of curves shows the differential amplifier output error due to the various resistor tolerance combinations. The OPA277 error contribution is nil. Note that using 1% resistors in a differential amplifier design can result in a worst- case CMRR error of 20mV per volt of common-mode voltage. This is only 36dB! (Circuit is created Neil P. Albaugh  TI-Tucson)

## Online Simulation of the Differential Amplifier Resistor Tolerance Analysis Circuit

The great feature of the TINA circuit simulator that you can analyze this circuit immediately with TINACloud the online version of TINA. Of course you can also run this circuit in the off-line version of TINA.

Click here to invoke TINACloud  and analyze the circuit yourself, or watch our tutorial video!

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Michael Koltai
www.tina.com

# Differential Amplifier CMRR Trim Circuit

Adding a negative- resistance circuit (U2) to the REF pin allows the CMRR of a differential amplifier or instrumentation amplifier to be trimmed. This is done by applying a sine wave of 20Vp-p to the inputs of U1 and adjusting the potentiometer P1 for a minimum signal at the amplifier output. By using an AC source the DC input offset errors do not effect this trim. At 50% rotation of P1 the resistance of R8 cancels the resistance of R5, appearing as a virtual ground to the REF pin. As P1 is adjusted from end to end, R5 is “undercancelled”or “overcancelled” by R8 and the resistance presented to the REF pin goes from a real, positive resistance to a negative resistance. This allows the internal resistor network of U1to be trimmed for maximum CMRR. ( Circuit is created by Neil P. Albaugh  TI – Tucson )

Differential Amplifier CMRR Trim Circuit

## Online Simulation of the Differential Amplifier CMRR Trim Circuit

The great feature of the TINA circuit simulator that you can analyze this circuit immediately with TINACloud the online version of TINA. Of course you can also run this circuit in the off-line version of TINA.