6 N6 _& i: l2 v& a6 }8 oFor a CFB amplifier the open-loop gain is ZT and its feedback factor is 1/RF, making the loop-gain TCFB = ZT/RF. 0 B g- \: A/ F v
The signal bandwidth is determined by RF and not by the circuit gain.% X. ~" n" a+ ]6 r" t0 V
The circuit gain is independently set with RS. 6 [- p! {7 n! N R+ Q8 CThe signal bandwidth remains stable for all gain settings . # _0 K* M: T% }# P2 f; OEven for unity-gain operation, an RF resistor is required.4 F& I: O7 E# ?
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.6 p2 E. L. a3 B
1 Q) [1 _* ?% m( O(1) The closed-loop gain can be modified by changing RS, leaving the closed-loop bandwidth unchanged. b0 |4 M* J5 f4 |(2) For a given RF, frequency compensation can be optimized. 1 b! j0 }& L" x* { T7 z2 N+ z(3)Suitable for high frequency applications. # W( m) b7 |& L* c; l
silde 1557: , S& W3 W. Z m. J% e1. Input offset: Bipolar is better than MOS( O: c& f1 S9 z1 ]/ h
KT/C = 26mV << MOS Vov- S" F. f( m' a$ T2 C5 p) Z
2. Mismatch 造成Randon offset ) y+ r H: I5 e2 @2 _& G
3. 電路不對稱所造成Systematic offset