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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. % x! c, n# m; Q) H$ j
The signal bandwidth is determined by RF and not by the circuit gain.: b! R9 W) }5 l5 F' ]6 ~
The circuit gain is independently set with RS.
$ Y9 H$ V! f# S5 rThe signal bandwidth remains stable for all gain settings .& }1 a$ R8 L; W8 v
Even for unity-gain operation, an RF resistor is required., j% [. e/ n- ]8 w) @& k( {2 Z
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.
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