slide 1010 1 }2 ^' A4 a; V& u$ l% q* ?) a4 L + X$ t" T- a1 Z( FFor a CFB amplifier the open-loop gain is ZT and its feedback factor is 1/RF, making the loop-gain TCFB = ZT/RF. ! @- `0 j r9 L8 k
The signal bandwidth is determined by RF and not by the circuit gain.1 ]+ u" z+ N. Y
The circuit gain is independently set with RS. ' _3 l) W4 B- H$ v' n; qThe signal bandwidth remains stable for all gain settings .' U% Y$ w8 i9 `6 e L
Even for unity-gain operation, an RF resistor is required. 6 n6 F6 _! L" K. {# ^0 TThe 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. & i3 G0 {! G' @6 Y* }3 Z
slide 1020 / G7 K* {/ ^& w7 t 4 f3 ~0 B# @9 {% z) N9 H(1) The closed-loop gain can be modified by changing RS, leaving the closed-loop bandwidth unchanged. , C; W' L( g' u3 o6 E+ h$ W(2) For a given RF, frequency compensation can be optimized.. c; U2 t+ F* l8 T e+ I r
(3)Suitable for high frequency applications. & u% B5 O3 D$ d; w
slide 218 7 t# Y9 K7 k7 B9 Z' H1 a0 E1. First order Sigma-Delta patterns in the output spectrum$ a5 W o! P5 ]" }2 e {; f
=> Idle tones(pattern noise, limit cycles)4 X ~* O6 V+ w' M; _7 f
2. Second order Sigma-delta 輸入太大時還是會不穩定