% S* _2 g9 L+ JFor a CFB amplifier the open-loop gain is ZT and its feedback factor is 1/RF, making the loop-gain TCFB = ZT/RF. / F0 O8 U' A& G" o1 q: [The signal bandwidth is determined by RF and not by the circuit gain.6 E- q/ v: \! e2 b6 r
The circuit gain is independently set with RS.; Q2 N; ]% f( Q7 f) P: U2 Q
The signal bandwidth remains stable for all gain settings .6 C& \7 J7 o9 ], D) n; T
Even for unity-gain operation, an RF resistor is required.. j$ E0 t/ o8 U% p7 d
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.- b7 L- Z5 T! [- h
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(1) The closed-loop gain can be modified by changing RS, leaving the closed-loop bandwidth unchanged.6 M. H+ g) I; A& V
(2) For a given RF, frequency compensation can be optimized. . O8 _" N6 Z3 U2 M# r9 g(3)Suitable for high frequency applications. / q( p& u7 T5 _% h d. S
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1. First order Sigma-Delta patterns in the output spectrum4 ~3 l' d) V9 R" w
=> Idle tones(pattern noise, limit cycles)$ z1 R9 N/ K7 G D/ T [! ~# o" n
2. Second order Sigma-delta 輸入太大時還是會不穩定