slide 1010 # }; O& N+ I1 n9 \) G ) c' c7 Z6 U# l6 ]) @2 J1 w% lFor a CFB amplifier the open-loop gain is ZT and its feedback factor is 1/RF, making the loop-gain TCFB = ZT/RF. . l' I1 ^# X7 S% A: E: y$ aThe signal bandwidth is determined by RF and not by the circuit gain.4 b5 U4 j4 p l" b. r* {
The circuit gain is independently set with RS. * |. x6 C3 I! o! D4 DThe signal bandwidth remains stable for all gain settings .8 I2 j9 y6 i% T& e! s+ Y( d
Even for unity-gain operation, an RF resistor is required.; A; `* ~) i* p9 d* z0 B' {* ?
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. 3 W2 K7 B6 m7 g8 Z+ r$ V
slide 1020/ W b/ B& ]: P' Z
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(1) The closed-loop gain can be modified by changing RS, leaving the closed-loop bandwidth unchanged.& D. G& X- s3 @- e# Y6 v& Y
(2) For a given RF, frequency compensation can be optimized.% Q! u! S8 d+ O4 X% {7 B
(3)Suitable for high frequency applications. 3 N4 o* ?5 |& V( v0 k$ p* ?9 r