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For a CFB amplifier the open-loop gain is ZT and its feedback factor is 1/RF, making the loop-gain TCFB = ZT/RF. % n" x% Q" n5 N0 q. IThe signal bandwidth is determined by RF and not by the circuit gain.0 R; p i- s( O7 A0 s5 s
The circuit gain is independently set with RS. " ~: o2 D* U0 b& m: O6 \The signal bandwidth remains stable for all gain settings . 4 L9 K0 i/ A( O. ~4 n2 I! n* g! bEven for unity-gain operation, an RF resistor is required.* [8 _ Z: Z# Z n$ s% P1 k6 V* {
The best practice when designing with CFB op-amps is to use the RF values given in the datasheet and to adjust the desired gain level through RS.' c/ Z2 E( n" ?
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(1) The closed-loop gain can be modified by changing RS, leaving the closed-loop bandwidth unchanged.6 l0 o# s- A1 V3 w* C5 l
(2) For a given RF, frequency compensation can be optimized. $ K' m5 a' z: H5 e* b% W9 s5 U. _(3)Suitable for high frequency applications.( u' }( \$ O0 e8 {# i( \* n