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