slide 1010 0 Q' }9 P" P4 _& m ( Y1 ?/ q' r, J4 @ ~ q( p2 {For a CFB amplifier the open-loop gain is ZT and its feedback factor is 1/RF, making the loop-gain TCFB = ZT/RF. ! {" k$ t' v3 O+ s3 w$ z2 Q
The signal bandwidth is determined by RF and not by the circuit gain. : x$ J7 @6 }" ~% |: F/ Y; FThe circuit gain is independently set with RS.( j0 G* z+ K) i8 P. W' g; R- ^
The signal bandwidth remains stable for all gain settings .& o: s1 r* w( X' c. n& r& \8 n
Even for unity-gain operation, an RF resistor is required. 2 h" L( D5 j0 L" x }! Q& v5 OThe 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.% M3 Y F" K, I. s3 b
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(1) The closed-loop gain can be modified by changing RS, leaving the closed-loop bandwidth unchanged. 6 h1 M8 e* q- h+ u(2) For a given RF, frequency compensation can be optimized.4 U" H" U8 ^7 ], M: @
(3)Suitable for high frequency applications. 6 o; z! N, P I: m1 {
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1. First order Sigma-Delta patterns in the output spectrum / u% j4 u. ~. s- w' b=> Idle tones(pattern noise, limit cycles)7 e: k( u9 k8 t6 M
2. Second order Sigma-delta 輸入太大時還是會不穩定