March 2020 StudentZone Quiz Solution

Question 1:

The faster amplifiers show a ringing settling characteristic. What circuit component(s) could you add to remove the ringing (perhaps at the cost of a longer settling time)?

Answer:

To reduce the ringing settling characteristic, the easiest way is to add a capacitor in parallel with the feedback resistor. This setup will work as an active low pass filter that will attenuate high frequencies, corresponding to the ringing. The value of the capacitor should be chosen properly to minimize as much as possible the settling time.

The updated circuit is presented in figure below.

With a value of 39pF for the capacitor (this value can be found also in the ADALP2000 Parts Kit for physical usage) the output of the op-amp (Vout) is presented in the figure below (red line), in comparison with the initial version of the circuit, without capacitor (blue line).

Question 2:

Try using lower value resistors for R1 and R2 (1KΩ for example) and a lower value for the potentiometer (5KΩ or lower). How does this change the settling waveforms you see if any?

Answer:

Lowering the values of the resistors will reduce the parasitic elements of the components, therefore the output of the op amp will have a less prominent settling time.

Plot for 10KΩ resistors:

Plot for 1KΩ resistors:



change Feb to March
[edited by: bsiegel at 2:12 PM (GMT 0) on 13 Jan 2020]