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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. % e- l* ^2 o' ?+ X4 s* ]The signal bandwidth is determined by RF and not by the circuit gain./ X( P0 V# |' o1 }5 X. s2 P6 K
The circuit gain is independently set with RS. ( v5 I( t& \ w1 k6 R f: T" nThe signal bandwidth remains stable for all gain settings .% O$ `* \8 Y+ {# B
Even for unity-gain operation, an RF resistor is required. ; f5 y: ^8 _% j/ [5 SThe 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. , M. e0 z1 k8 r0 n9 X4 }
$ l5 P5 q. x n5 m) h(1) The closed-loop gain can be modified by changing RS, leaving the closed-loop bandwidth unchanged. 6 Q" I" A, C, \2 k(2) For a given RF, frequency compensation can be optimized. 1 F* Q) b/ W6 O T& e2 d(3)Suitable for high frequency applications." D% P" J& e- y; T, h1 x, o) @& `
slide 218 , F. {" t3 R) y% {* s1 |% t% t1. First order Sigma-Delta patterns in the output spectrum , Y5 E$ _% O7 `- r9 z=> Idle tones(pattern noise, limit cycles)# v# b; d s$ w' J
2. Second order Sigma-delta 輸入太大時還是會不穩定