Current feedback op-amps
Current feedback op-amps
Current feedback op-amps
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Gain calculation – frequency response (2)<br />
G NINV <br />
ZZ F ZZ G<br />
ZZ G Z B Z F Z B Z G Z F Z G<br />
Z T <br />
Z 0<br />
1s 1 1s 2 <br />
Neglect Z B<br />
since it is much smaller than anything else. Then,<br />
Z<br />
NINV<br />
<br />
( + ) ⎛ ⎞ 1<br />
Z ZF ZG ZF<br />
= ⎜1+<br />
⎟<br />
ZZG + ZFZG ⎝ ZG ⎠1 + ZF<br />
/ Z<br />
<br />
Gain<br />
Bandwidth<br />
Observe that the gain and bandwidth have been decoupled.<br />
The bandwidth depends only on Z F<br />
(and Z B<br />
, really), while the<br />
gain depends on both Z F<br />
and Z G<br />
There is no magic involved. The CFOA is a dominant pole<br />
transimpedance amplifier, while the voltage and current buffers have<br />
poles at much higher frequencies.
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