Gain margin and phase margin Assume you have an operational amplifier whose gain function is…

Gain margin and phase margin Assume you have an operational amplifier whose gain function is characterized by: DC open-loop gain; A dominant pole; Either two non-dominant (high-frequency) poles, or a non-dominant pole and a right half-plane (RHP) zero. The parameters that characterize this op amp are its dc open-loop gain, the break frequency of the dominant pole, and the break frequencies of the non-dominant pole(s) and the RHP zero (if applicable). Assume also that you place this op amp in a negative feedback loop with feedback ratio b. Create an Excel spreadsheet to compute and plot the

»Gain margin and phase margin Assume you have an operational amplifier whose gain function is characterized by: DC open-loop gain; A dominant pole; Either two non-dominant (high-frequency) poles, or a non-dominant pole and a right half-plane (RHP) zero. The parameters that characterize this op amp are its dc open-loop gain, the break frequency of the dominant pole, and the break frequencies of the non-dominant pole(s) and the RHP zero (if applicable). Assume also that you place this op amp in a negative feedback loop with feedback ratio b. Create an Excel spreadsheet to compute and plot the loop gain of this op amp with feedback over a frequency range from 1Hz to 100MHz or 1GHz (your choice). The graph should be a Bode plot with a logarithmic frequency scale and separate y -axes for loop gain (dB) and phase of the loop gain (degrees). Choose the break frequencies of the poles (and RHP zero, if applicable) such that the phase crosses -180° at some frequency between 1MHz and 20MHz. Then choose a value for the dc open-loop gain such that you have a gain margin of -12 to -20dB with b = 1. Create a Word file in which to record your work for each of the following sections: 1. Calculate the Bode plot of loop gain with b = 1. Copy the Bode plot to the Word file and include the op amp parameters, gain margin, phase margin, b, and dc closed-loop gain. 2. Now determine the value of b that gives a gain margin of +6dB. Copy the resulting Bode plot to the Word file and include the op amp parameters, gain margin, phase margin, b, and dc closed-loop gain. 3. Now reset the value of b to 1. Move the dominant pole to a frequency that produces a gain margin of +6dB. Copy the resulting Bode plot to the Word file and include the op amp parameters, gain margin, phase margin, b, and dc closed-loop gain. The dc open-loop gain should be between 5000V/V and 250,000V/V. The break frequencies of the poles (and RHP zero, if applicable) are up to you, but the open-loop gain of the op amp should show definite dominant-pole behavior. The break frequencies of the non-dominant pole(s) and RPH zero (if applicable) should be higher by a factor of 100 or more than the break frequency of the dominant pole. Examples: Example Bode plot of loop gain for the parameters given above. This loop gain shows a gain margin of approximately -15dB and a phase margin of -53°.

»