slide 1010 7 }1 [% \ p: \! ~# ^6 ]% T3 U, P 3 X* o' h8 Q8 `For a CFB amplifier the open-loop gain is ZT and its feedback factor is 1/RF, making the loop-gain TCFB = ZT/RF. 8 r( _: K5 q9 `. z. HThe signal bandwidth is determined by RF and not by the circuit gain.! g" K3 P4 \. [$ @6 V
The circuit gain is independently set with RS. & _4 M0 I2 K8 {) G/ X% {7 Y CThe signal bandwidth remains stable for all gain settings .8 L- v& g( ?3 g: A o5 e8 g
Even for unity-gain operation, an RF resistor is required.* a0 h" g2 J2 {' S) n
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. ! ]2 K3 ` g* q$ I
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(1) The closed-loop gain can be modified by changing RS, leaving the closed-loop bandwidth unchanged.& s% f2 t, o5 w, g" }: I# g
(2) For a given RF, frequency compensation can be optimized.3 ?: v! V: n8 l; N
(3)Suitable for high frequency applications. H1 @) ^' {$ ]) B6 z+ R