! P* S, m4 l0 r. T9 \7 HFor a CFB amplifier the open-loop gain is ZT and its feedback factor is 1/RF, making the loop-gain TCFB = ZT/RF. & C% f$ \( |3 H( m& hThe signal bandwidth is determined by RF and not by the circuit gain. 8 B n! s+ }# A! E5 [9 Q7 BThe circuit gain is independently set with RS. 3 ]7 V) O1 F% R GThe signal bandwidth remains stable for all gain settings .6 M( k4 K( x: g+ _& l
Even for unity-gain operation, an RF resistor is required. 6 h/ q" o) S7 I1 @/ Z+ S; ]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 l/ V# f" d: j w
slide 1020 * |( Q9 p8 ]/ [ M" ]8 {; O2 Q) A# C- X& g
(1) The closed-loop gain can be modified by changing RS, leaving the closed-loop bandwidth unchanged. H! {* @) s) i/ V& N& x
(2) For a given RF, frequency compensation can be optimized.' U& i0 M) u0 D7 h @8 u6 f# ~# m* ~
(3)Suitable for high frequency applications. 9 w; c" W6 H2 a3 M0 s& a