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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.
! e0 S( W: [; X7 ?" R% SThe signal bandwidth is determined by RF and not by the circuit gain.0 {* t& x. M% d5 X/ y
The circuit gain is independently set with RS.
' @$ O& k4 h, r( K! z. q2 JThe signal bandwidth remains stable for all gain settings .; P4 X! E# k" M0 J
Even for unity-gain operation, an RF resistor is required.5 j5 z4 G0 l( j: k
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.* e' D4 Y; ^3 y6 {5 m/ N
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