slide 1010 ( I4 n) p1 v* p9 h / L& L+ ]9 O( c1 K$ H8 F# vFor a CFB amplifier the open-loop gain is ZT and its feedback factor is 1/RF, making the loop-gain TCFB = ZT/RF. 1 v- {$ O4 j8 e5 E0 @4 X+ u
The signal bandwidth is determined by RF and not by the circuit gain.2 ~, |' `9 k0 A3 I ~2 m* H7 q3 l
The circuit gain is independently set with RS. ' d! e1 i8 O. LThe signal bandwidth remains stable for all gain settings . % V# ]3 {9 I6 {4 B3 P SEven for unity-gain operation, an RF resistor is required.* R" b. G) Z# u/ r1 S* h3 t' G' g
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. ( Y+ X8 ~( O$ O8 s8 O
slide 1020 2 H( t6 J1 v6 D, i2 ~& r/ ]* }% }5 K$ h4 z, K
(1) The closed-loop gain can be modified by changing RS, leaving the closed-loop bandwidth unchanged.7 g4 u$ k1 ?1 O& R
(2) For a given RF, frequency compensation can be optimized. ) H4 {' j* M4 k% A; M8 q& S(3)Suitable for high frequency applications. 4 v! v) a2 o' w8 @: m4 q: R" o$ i