September 2021 StudentZone Quiz Solution

Question 1:

1. For the circuit in Figure 1, explain how the R6 potentiometer affects the output signal, when set to minimum/maximum resistance value.

Build the circuit in Figure 1, using LTspice software tool. A circuit example is presented in figure below. Set the value of the potentiometer R6 to 50% and plot the input and output signal. We might notice that the output signal (V2+) has a sine wave shape on both the positive and negative half.

Now set the potentiometer value to minimum and plot the input and output signals. The negative half of the output signal has a more pronounced sine wave shape, while the positive half has a similar shape to the input triangle wave.

Similar, when the potentiometer is set to its maximum value, the output signal will have the negative half similar to the input signal, while the positive half will have a pronounced sine wave shape.

• Might also be worth pointing out the subtle trick used on the triangle wave generator - buffering a red LED with an emitter follower roughly cancels their temperature coefficients...