CS3001
CS3002
3.2
Open-loop Gain and Stability Compensation
3.2.1
Discussion
The CS3001 and CS3002 achieve ultra-high open capacitance adds an additional pole in the loop gain
loop gain. Figure 16 illustrates the amplifier in a transfer function at a frequency of f = 1/(2πR*C )
in
non-inverting gain configuration. The open loop where R is the parallel combination of R1 and R2
gain and phase plots indicate that the amplifier is (R1 || R2). A higher value for R produces a pole at
stable for closed-loop gains less than 50 V/V and a lower frequency, thus reducing the phase margin.
R1 ≤ 100 Ohms. For a gain of 50, the phase margin R1 is recommended to be less than or equal to 100
is between 40° and 60° depending upon the loading ohms, which results in a pole at 30 MHz or higher.
conditions. As shown in Figure 17, on page 12, the If a higher value of R1 is desired, a compensation
operational amplifier has an input capacitance at
capacitor (C2) should be added in parallel with R2.
the + and – signal inputs of typically 50 pF. This C2 should be chosen such that R2*C2 ≥ R1*C .
in
RS
Vin
Vo
R2
R1
Figure 16. Non-inverting Gain Configuration
DS490F8
9
CIRRUS [ CIRRUS LOGIC ]
