slide 1010 + P5 h6 F4 h- y) C5 m 8 f. {' J |9 j+ _* t- b" v0 PFor a CFB amplifier the open-loop gain is ZT and its feedback factor is 1/RF, making the loop-gain TCFB = ZT/RF. ; C$ z8 o' m2 u- BThe signal bandwidth is determined by RF and not by the circuit gain. 8 j s+ x8 S E8 _% i2 u. D" VThe circuit gain is independently set with RS.& @! T6 f! p) ?
The signal bandwidth remains stable for all gain settings .4 t$ ^" x" ^) F- k) x) v( r* u
Even for unity-gain operation, an RF resistor is required.8 T) s; s& Q. L! {5 H% A* J) y0 o# O
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. 0 K6 D- d# |' R& t* J) \) l) [ D
slide 1020 8 V, z. s) B$ [7 C& F; }/ r, ~. d) y$ l5 N8 F
(1) The closed-loop gain can be modified by changing RS, leaving the closed-loop bandwidth unchanged.1 |. [1 P( E6 p* V, _1 t
(2) For a given RF, frequency compensation can be optimized. ) D$ q8 t( ?( K- }6 n4 o" j(3)Suitable for high frequency applications.' d4 i) ?. b: O$ H# ~# K$ c' L
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1. First order Sigma-Delta patterns in the output spectrum/ L, L6 K' b/ B# k- I \
=> Idle tones(pattern noise, limit cycles) / u4 o1 ?3 m, [# ?2. Second order Sigma-delta 輸入太大時還是會不穩定