CS3011
CS3012
3.2
Open Loop Gain and Stability Compensation
3.2.1
Discussion
The CS3011 and CS3012 achieve ultra-high open
loop gain. Figure 15 illustrates the amplifier in a
non-inverting gain configuration. The open loop
gain and phase plots indicate that the amplifier is
stable for closed-loop gains less than 50 V/V. For
a gain of 50, the phase margin is between 40° and
60° depending upon the loading conditions. As
shown in Figure 16 on page 11, the op amp has an
input capacitance at the + and – signal inputs of
typically 50 pF. This capacitance adds an addition-
al pole in the loop gain transfer function at a fre-
quency of f = 1/(2πR*Cin) where R is the parallel
combination of R1 and R2 (R1 || R2). A higher val-
ue for R produces a pole at a lower frequency, thus
reducing the phase margin. R1 is recommended to
be less than or equal to 100 ohms, which results in
a pole at 30 MHz or higher. If a higher value of R1
is desired, a compensation capacitor (C2) should
be added in parallel with R2. C2 should be chosen
such that R2*C2 ≥ R1*Cin.
RS
Vin
Vo
R2
R1
Figure 15. Non-Inverting Gain Configuration
10
DS597F5
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