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For a CFB amplifier the open-loop gain is ZT and its feedback factor is 1/RF, making the loop-gain TCFB = ZT/RF. ; G9 r( { t5 Z5 `5 l; q" K7 Y/ tThe signal bandwidth is determined by RF and not by the circuit gain.' q5 }5 J1 b0 C) O
The circuit gain is independently set with RS. 0 [ S2 D# ^1 _The signal bandwidth remains stable for all gain settings . t2 C8 k+ T3 kEven for unity-gain operation, an RF resistor is required.* d& r; j$ j* {& @
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.- o1 R8 I8 n1 Q" b# m
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(1) The closed-loop gain can be modified by changing RS, leaving the closed-loop bandwidth unchanged.. E* W9 U+ \7 S2 }
(2) For a given RF, frequency compensation can be optimized. 0 _" R; l4 l9 ^8 @# F# X(3)Suitable for high frequency applications.: ~% p: i# b7 @; S4 M1 t4 d
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1. First order Sigma-Delta patterns in the output spectrum5 v# {0 C5 T' @6 Y2 O, ]$ g$ R
=> Idle tones(pattern noise, limit cycles): A# h6 D% N9 s+ r
2. Second order Sigma-delta 輸入太大時還是會不穩定