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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. 6 [* i# W8 D! [. \
The signal bandwidth is determined by RF and not by the circuit gain. 3 O7 U1 C, U* `7 O1 ^- N. R* TThe circuit gain is independently set with RS.% m; b" O. e! s5 y% A$ v# E+ G
The signal bandwidth remains stable for all gain settings . 3 Y+ _6 L( p4 C1 E% N( v2 _( ?. [Even for unity-gain operation, an RF resistor is required.: f6 D# J$ B% r" W$ ~8 K- a3 j
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. & z. R0 a( B- N Y$ d
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(1) The closed-loop gain can be modified by changing RS, leaving the closed-loop bandwidth unchanged.4 L- [/ _) L$ F9 v x% s
(2) For a given RF, frequency compensation can be optimized.' h$ R( D% u3 Y% x8 J, L5 Q/ T
(3)Suitable for high frequency applications.. d5 E: E+ n: c* h M, K6 A# i