slide 1010 4 S2 V& O8 K% M s; N ! k" i1 I3 V2 T4 G& v2 {For a CFB amplifier the open-loop gain is ZT and its feedback factor is 1/RF, making the loop-gain TCFB = ZT/RF. 9 s( q# c* B$ N% A+ w9 H
The signal bandwidth is determined by RF and not by the circuit gain. 7 q4 v5 C) z+ u& M7 Y! iThe circuit gain is independently set with RS. 5 f# [2 c% }; W& z( Z" cThe signal bandwidth remains stable for all gain settings .# Z( _3 }) _9 C; x+ g! H5 A* x5 _
Even for unity-gain operation, an RF resistor is required.9 {3 y+ V+ o: |. m
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 b: t7 \6 F' n* B' A( [
n& h3 J5 Y, ]7 s' i: R+ D: V(1) The closed-loop gain can be modified by changing RS, leaving the closed-loop bandwidth unchanged./ N. i8 J3 J7 [9 L4 Q* W$ l) }2 E
(2) For a given RF, frequency compensation can be optimized.' M9 M$ S2 p ^, q+ ^
(3)Suitable for high frequency applications./ k: J$ O+ M" e4 M. d' t) F# Q