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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. 8 @: ~/ h* i# W( _ |2 D( q: E QThe signal bandwidth is determined by RF and not by the circuit gain.. M8 Y9 H2 b4 d3 n
The circuit gain is independently set with RS. ) p/ `* x" o$ DThe signal bandwidth remains stable for all gain settings .8 T a- ~. o3 R( f" b' W
Even for unity-gain operation, an RF resistor is required.$ ^# v0 \8 A B
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. 6 G2 {' |. `1 o8 z/ J
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(1) The closed-loop gain can be modified by changing RS, leaving the closed-loop bandwidth unchanged.4 B2 X$ y4 ?* d0 _' @! p9 I
(2) For a given RF, frequency compensation can be optimized. ( z( U. D5 C6 y7 `! R7 {1 I(3)Suitable for high frequency applications.6 e' f. q' i% c" e