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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. : W, K* Q) R" [7 u& \
The signal bandwidth is determined by RF and not by the circuit gain.' A, s- v/ D3 U
The circuit gain is independently set with RS. # X3 \: {+ ~+ M, }- wThe signal bandwidth remains stable for all gain settings .) N0 @4 j; j; e% o
Even for unity-gain operation, an RF resistor is required. p7 [- c9 O9 V9 {9 Y, D
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.0 D7 ^. ?. L- L& P
slide 1020 . E P6 b* I- J) M0 S3 h' K7 _9 B! p# @! H% B' c9 S4 ^
(1) The closed-loop gain can be modified by changing RS, leaving the closed-loop bandwidth unchanged.$ d% R/ J9 p' e
(2) For a given RF, frequency compensation can be optimized. , M/ m4 E1 I! H% M(3)Suitable for high frequency applications.6 @$ T" w9 D' n3 w3 W+ ~- |0 `