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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 ~+ ^" K) y# @: D" jThe signal bandwidth is determined by RF and not by the circuit gain. # q! m& ~. X) }9 [The circuit gain is independently set with RS. $ x7 u5 f( K0 V! W; jThe signal bandwidth remains stable for all gain settings .2 G+ ^3 h4 d; f- @
Even for unity-gain operation, an RF resistor is required. |# {& R9 g2 U# CThe 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.- j" x$ D# ~$ V
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(1) The closed-loop gain can be modified by changing RS, leaving the closed-loop bandwidth unchanged. " W5 r$ [, d9 `# c$ q, a(2) For a given RF, frequency compensation can be optimized. 6 O9 p$ J; J' H9 [(3)Suitable for high frequency applications.. u o2 i1 K# U! T