6 g$ [9 h& {/ I$ s* w8 J8 \$ m% a( ^For a CFB amplifier the open-loop gain is ZT and its feedback factor is 1/RF, making the loop-gain TCFB = ZT/RF. # N- l( u0 v Q8 G2 I9 D7 ? G
The signal bandwidth is determined by RF and not by the circuit gain. & ~0 B( c+ H* h0 B* D: o8 O4 ]8 WThe circuit gain is independently set with RS.# w/ P+ W* ~$ j$ t
The signal bandwidth remains stable for all gain settings .5 b1 l8 S& x' _2 ^. I9 N
Even for unity-gain operation, an RF resistor is required. # r) Q/ `8 z& w: ~! E" A0 ~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.! H: p# f6 u& y! F+ f" ~: |& |
slide 1020 ( j: v; d2 W4 l6 x: V& A' t7 M4 D4 A# b- |
(1) The closed-loop gain can be modified by changing RS, leaving the closed-loop bandwidth unchanged.. q" n* p* n* z% e) B# x! I8 I/ J
(2) For a given RF, frequency compensation can be optimized. / g7 s( g) c5 q* q! h8 g(3)Suitable for high frequency applications. 8 }4 l X/ ~* m5 G* [