certain op-amp has the open-loop response in Figure 7–19 . As you can see, the lowest closed-loop gain for which stability is assured is approximately 40 dB (where the closed-loop gain line still intersects the -20 dB/decade slope). In a particular application, a 20 dB closed-loop gain is required.

Question

(a) Determine the critical frequency for the compensating network.

(b) Sketch the ideal response curve for the compensating network.

(c) Sketch the total ideal compensated open-loop response.

Accepted Answer

(a) The gain must be dropped so that the -20 dB/decade roll-off extends down to 20 dB rather than to 40 dB. To achieve this, the midrange open-loop gain must be made to roll off a decade sooner. Therefore, the critical frequency of the compensating network must be 10 Hz.

(b) The roll-off of the compensating network must end at 100 Hz, as shown in Figure 7–20 (a).
(c) The total open-loop response resulting from compensation is shown in Figure 7–20 (b).

P R A C T I C E EXERCISE

In this example, what is the uncompensated bandwidth? What is the compensated bandwidth?

Question 7.6: certain op-amp has the open-loop response in Figure 7–19 . A...

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