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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. 2 F6 n8 U- I9 M2 o; b7 A3 tThe signal bandwidth is determined by RF and not by the circuit gain.0 }; d% x: ? f5 T! n
The circuit gain is independently set with RS.- O4 n" G) o; s! k
The signal bandwidth remains stable for all gain settings .! Q# n9 ^8 w4 c
Even for unity-gain operation, an RF resistor is required.8 \8 w5 a; `5 R$ J. ?
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.& {9 _* k# _) t1 X; S' C
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(1) The closed-loop gain can be modified by changing RS, leaving the closed-loop bandwidth unchanged.# z2 {7 L: T) k( L
(2) For a given RF, frequency compensation can be optimized. # t# K5 k, z, q# V(3)Suitable for high frequency applications. [+ X: F1 O G6 m8 s9 i