slide 1010, H. _# Y! K' D! D
8 Y7 l7 `' Q( O' ?4 ?$ J
For a CFB amplifier the open-loop gain is ZT and its feedback factor is 1/RF, making the loop-gain TCFB = ZT/RF. [( u. |1 e0 B3 m0 I8 p
The signal bandwidth is determined by RF and not by the circuit gain. 5 _! A) C% d+ h tThe circuit gain is independently set with RS." B: q2 `9 j. A
The signal bandwidth remains stable for all gain settings .2 N7 I% G% |$ ^( I4 _2 f) L
Even for unity-gain operation, an RF resistor is required. O% [6 R( P2 B- d- \ IThe 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.: q: E. k: y1 [! x9 b8 I0 G
% H/ u) a! r2 i- u0 \(1) The closed-loop gain can be modified by changing RS, leaving the closed-loop bandwidth unchanged. 2 a; Y1 O, l/ J2 u* I(2) For a given RF, frequency compensation can be optimized. & { j; L2 i; b# ], [2 Z9 W: [/ D(3)Suitable for high frequency applications. " v1 _7 Z; J1 z# ]9 @# c
silde 1557: . @& R2 ~' x t$ L8 |0 z& `1. Input offset: Bipolar is better than MOS* d2 \5 Z4 F: A M; A
KT/C = 26mV << MOS Vov + H, d( e9 p0 ~$ j: F! ]2. Mismatch 造成Randon offset ( K, L; A f _$ e R
3. 電路不對稱所造成Systematic offset