CS3001
CS3002
Vin
C
in
50 pF
Vo
50 pF
C
in
R2
R1
C2
Choose C2 so that R2
•
C2
≥
R1
•
C
in
?
Figure 17. Non-inverting Gain Configuration with Compensation
The feedback capacitor C2 is required for closed-
loop gains greater than 50 V/V. The capacitor in-
troduces a pole and a zero in the loop gain transfer
function,
s-
–
⎛
1 + ----
⎞
⎝
z
1
⎠
-
T = ---------------------- A
ol
s
⎛
1 + ----
⎞
-
⎝
p
1
⎠
1
1
-
-
P
1
= ------------------------------------
≅
------------------------
||
R
2
)C
2
2π
(
R
1
C
2
)
2π
(
R
1
for
R
2
» R
1
1
Z
1
= -----------------------------------
2π
(
A
×
R
1
)C
2
where
R
2
-
A = -----
R
1
1
-
Z
1
= ------------------------
2π
(
R
2
)C
2
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).
10
DS490F8
CIRRUS [ CIRRUS LOGIC ]
