CS3001

CS3002

DS490F9

9

3.2

Open-loop Gain and Stability Compensation

3.2.1

Discussion

The CS3001 and CS3002 achieve ultra-high open

loop gain. Figure 16 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 and

R1

≤ 100 Ohms. For a gain of 50, the phase margin

is between 40

° and 60° depending upon the loading

conditions. As shown in Figure 17, on page 10, the

operational amplifier has an input capacitance at

the + and – signal inputs of typically 50 pF. This

capacitance adds an additional pole in the loop gain

transfer function at a frequency of f = 1/(2

where R is the parallel combination of R1 and R2

(R1

|| R2). A higher value 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*C

R1

R2

Vin

Vo

R

S

Figure 16. Non-inverting Gain Configuration