0 T* \2 f- j: EFor a CFB amplifier the open-loop gain is ZT and its feedback factor is 1/RF, making the loop-gain TCFB = ZT/RF. 7 I9 z( w/ c0 ]; ?6 [. xThe signal bandwidth is determined by RF and not by the circuit gain.8 F% S3 Z- N8 X8 G4 O& i: \
The circuit gain is independently set with RS.& m6 ^" H2 T3 u7 J, ?+ I
The signal bandwidth remains stable for all gain settings .6 _% @4 a* g- B8 W n$ ]
Even for unity-gain operation, an RF resistor is required.4 p2 C& Y; p3 g" U8 a
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.4 j/ \9 z" \; E% K
slide 1020/ Y9 s5 W0 Y/ W/ D
% A; V9 b) c* z3 V3 O8 V
(1) The closed-loop gain can be modified by changing RS, leaving the closed-loop bandwidth unchanged.+ _) w0 t4 H6 ]8 t5 S8 m- Z
(2) For a given RF, frequency compensation can be optimized. 3 ~0 f$ ?$ }/ I! A8 L. M(3)Suitable for high frequency applications.+ ]1 V, w0 ?( L b; ^/ j0 e
slide 218 ! T. [# Y6 q7 m8 O9 \1. First order Sigma-Delta patterns in the output spectrum* ^6 K* l% R2 B" _* O8 P
=> Idle tones(pattern noise, limit cycles) ! T+ i6 G. `3 M; p2. Second order Sigma-delta 輸入太大時還是會不穩定