Sep, 2015

Calculates the exact voltage gain A

The above circuit is a fairly general inverting amplifier configuration with a t-network in the feedback loop. This type of t-network enables high gains to be achieved in the inverting amplifier configuration without the use of high feedback resistance values. Since the midband gain of the single-feedback-resistance inverting amplifier configuration is -Rf/Ri and Ri involves the source inpedance, high values of source impedance would require very high Rf values in the single feedback impedance case, compared to the t-network configuration. For the t-network configuration, for an ideal op-amp with infinite GBW, the midband gain (assuming all shunt capacitative impedances are very high, and Rs << R0||R1) is:

where R

Assuming the high-frequency rolloff is determined by the feedback network (and not limited by the GBW of the op-amp), if C2 and C3 are small enough, the -3db high frequency is determined by the pole formed by R

However, it must be noted that feedback analysis of this circuit with a feedback t-network shows that the

The response curves below show the open-loop gain profile for a 10MHz op-amp with single-pole rolloff, noise gain, and amplifier response for the circuit shown above. Responses for both an ideal (infinite GBW op-amp) and the 10MHz GBW op-amp are shown. Note that the mid-band noise gain is about 10db higher than the signal gain, a consequence of the t-network. By comparison, a simple inverting op-amp circuit with a single feedback resistor of the same value as the equivalent for the t-network (1.032 Mohm) would have a noise gain of 27.2db, almost identical to the signal gain of 26.8db with a considerably higher f3db circuit BW of 200kHz: