slide 1010 6 ~4 E. K9 u, H) E' Y 7 M/ q3 g% m, m# \: X8 L# uFor a CFB amplifier the open-loop gain is ZT and its feedback factor is 1/RF, making the loop-gain TCFB = ZT/RF. # b8 T) _$ U2 }. j$ T5 C8 ZThe signal bandwidth is determined by RF and not by the circuit gain.# Q5 m( M6 v0 {1 ]& A0 _. Y6 n
The circuit gain is independently set with RS. ( i1 O6 {6 u+ W6 r3 CThe signal bandwidth remains stable for all gain settings . ; l* F1 T. W9 v$ q$ kEven for unity-gain operation, an RF resistor is required. : O1 Y& }; _% @% H. ^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. 7 B( T0 \" Q7 z
% c% b$ M8 y5 ?4 _(1) The closed-loop gain can be modified by changing RS, leaving the closed-loop bandwidth unchanged. : X% s. W9 x, ]2 t(2) For a given RF, frequency compensation can be optimized. ( B9 L9 a7 X) T9 r6 Z(3)Suitable for high frequency applications. 9 |$ ~3 P" t7 P9 g* y