9 q! }7 c9 S/ P' }For a CFB amplifier the open-loop gain is ZT and its feedback factor is 1/RF, making the loop-gain TCFB = ZT/RF. & W! {$ w/ j4 xThe signal bandwidth is determined by RF and not by the circuit gain. ; n7 X9 H1 n( l0 N; T& v9 _% qThe circuit gain is independently set with RS.2 w: Y2 m3 @2 s
The signal bandwidth remains stable for all gain settings . : z2 Y( h8 T7 X0 l- NEven for unity-gain operation, an RF resistor is required. 8 t0 W5 U* G/ A' t JThe 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.3 A7 ~& U( c( d! m9 V; u
slide 1020 % p$ z I) ]4 r0 ?) o& M# m7 ?5 K/ [8 j3 a
(1) The closed-loop gain can be modified by changing RS, leaving the closed-loop bandwidth unchanged. $ }, p$ G) J: l, w(2) For a given RF, frequency compensation can be optimized.1 o% q( f2 \- l8 J) o
(3)Suitable for high frequency applications.2 e7 |# \2 \+ J- R; K8 W