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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. 4 z- M# S! C t5 J
The signal bandwidth is determined by RF and not by the circuit gain. * {* B9 d1 J& ` s; r$ zThe circuit gain is independently set with RS. 8 Y" f# m. o9 c& A" a/ QThe signal bandwidth remains stable for all gain settings . E L! X; \3 D9 v" T+ P! h: z
Even for unity-gain operation, an RF resistor is required. 3 ~$ x8 D! ?* p- k: m% x( Z, Z) CThe 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. " D( ^; v# I- P0 P, c
slide 1020 8 M2 l6 A+ k' [1 c& j, A% n 1 u0 ]0 k7 F# ~, \, G Z(1) The closed-loop gain can be modified by changing RS, leaving the closed-loop bandwidth unchanged. + u3 M" G) G: a" s% g(2) For a given RF, frequency compensation can be optimized.( `& g& u3 M9 }' {
(3)Suitable for high frequency applications.: s: Z! }$ U8 W( u% k% y9 l
slide 218 # s! @1 Y4 V( w; X5 \0 g0 H1 o. f- W1. First order Sigma-Delta patterns in the output spectrum5 w7 c _: ?5 x/ n2 w2 r
=> Idle tones(pattern noise, limit cycles) 8 p; l& b+ \% c1 b; B D2. Second order Sigma-delta 輸入太大時還是會不穩定