How does the open-loop gain vary with frequency?
The open-loop gain falls at 6 dB/octave. This means that if we double the frequency, the gain falls to half of what it was. Conversely, if the frequency is halved, the open-loop gain will double, as shown in Figure 1-8. This gives rise to what is known as the Gain-Bandwidth Product.
Why is frequency compensation required in amplifiers?
It usually has two primary goals: To avoid the unintentional creation of positive feedback, which will cause the amplifier to oscillate, and to control overshoot and ringing in the amplifier’s step response. It is also used extensively to improve the bandwidth of single pole systems.
How is the loop gain of an amplifier determined?
This error signal is subjected to the open loop gain of the amplifier (A0) to produce the output voltage: This is rearranged to find the closed loop gain of the amplifier: In most op amp circuits the open loop gain of the amplifier is very high, i.e. much greater than the “1” in the denominator, allowing the closed loop gain approximation:
What happens when the open loop gain increases?
Basic op amp theory states that the two input voltages regulate to the same voltage, a suitable assumption at very high open loop gains, but what happens as the open loop gain reduces with increasing signal frequency?
Why does an amplifier have to have compensation?
The text says that “the amplifier requires compensation because its basic open loop gain is still higher at frequency where internal phase shift are reaching 180 degrees..This turn negative feedback to positive at higher frequencies which causes oscillation.”
How does frequency compensation affect the op amp?
This frequency compensation is used to ensure that the op amp remains stable under all operating conditions. The very earliest op amps were prone to instability and as a result, compensation was introduced into virtually all op amp IC designs as a matter of course. The effect of the compensation on the op-amp bandwidth is to reduce the break point.