CS3011
CS3012
Vin
Cin
50 pF
50 pF
Vo
Cin
R2
C2
R1
Choose C2 so that R2 • C2 ≥ R1 • Cin
?
Figure 16. Non-Inverting Gain Configuration with Compensation
The feedback capacitor C2 is required for closed-
loop gains greater than 50 V/V. The capacitor intro-
duces a pole and a zero in the loop gain transfer
function.
s
⎛
⎞
----
– 1 +
⎝
⎠
z1
----------------------
T =
Aol
s
p1
⎛
⎞
----
1 +
⎝
⎠
1
1
------------------------------------ ------------------------
P1
Z1
Z1
=
=
≅
for
R2 » R1
||
2π(R1 R2)C2 2π(R1C2)
R2
-----
R1
1
-----------------------------------
where
A =
2π(A × R1)C2
1
------------------------
=
2π(R2)C2
This indicates that the separation of the pole and
the zero is governed by the closed loop gain. It is
required that the zero falls on the steep slope
(–100 dB/decade) of the loop gain plot so that
there is some gain higher than 0 dB (typically 20
dB) at the hand-over frequency (the frequency at
which the slope changes from – 100 dB/decade to
–20 dB/decade).
DS597F5
11
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