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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. % Q. @: r7 a% s! ]5 i, C
The signal bandwidth is determined by RF and not by the circuit gain. ; D3 ^6 k& z2 k3 B! CThe circuit gain is independently set with RS. * g) d7 w5 g0 W& D; c0 P) @The signal bandwidth remains stable for all gain settings . 2 I% e! @+ R$ w1 u7 KEven for unity-gain operation, an RF resistor is required." j7 I# _2 [! S$ ^& ^. Y
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.+ w" p h1 |/ E( i% \
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(1) The closed-loop gain can be modified by changing RS, leaving the closed-loop bandwidth unchanged.0 t% R* I/ S$ E6 o: A4 ]
(2) For a given RF, frequency compensation can be optimized. ) D! v$ J% ?# `) p( `(3)Suitable for high frequency applications.1 j' i k3 q0 |* k- ]# V5 @0 x- F
slide 218 ; K1 p1 Q9 w) b: f; w A# K# h1. First order Sigma-Delta patterns in the output spectrum: [6 v3 I) n8 Y6 v
=> Idle tones(pattern noise, limit cycles); g8 K! \: I: c
2. Second order Sigma-delta 輸入太大時還是會不穩定