Task 4: Ring oscillator An a-stable multivibrator oscillates automatically between two semi-stable states. It has no stable states. There are different ways of construct a-stable multivibrators, but the type of multivibrator used here is a ring oscillator. The rate of oscillation is determined by the propagation delays of the components. Figure 4 shows a ring oscillator consisting of five 74LS14 Schmitt trigger inverters in a closed loop. This circuit is not stable; it is astable. That is, no point in the circuit assumes a particular voltage and stays there. Based on your knowledge so far, analyse this "ring oscillator circuit. Assume that at some point a low-to-high transition occurs and then follow the effect of this transition around the loop. After one pass around the loop, the transition returns to the starting point with the opposite sign. After two laps around the loop, the circuit is again in the starting state. U1A U2A U3A U4A U5A 74LS14D 74LS14D 74LS14D 74LS14D 74LS14D Figure 4: A ring oscillator For this task you need to: . • • Build the circuit using Multisim. While you are placing the inverters check what the propagation delay is using the detail report. Connect the output to the input of an oscilloscope, connect the negative input of the oscilloscope to Ground. Simulate and make screenshots. You will probably need to adjust both the time base of the oscilloscope and the scale of the input channel to clearly see the oscillations on the screen. Measure the period of oscillation with the oscilloscope. Calculate the period of oscillation based on the propagation delays of the gates you found in the detail report. Answer the following questions: 。 Would the ring oscillator also work if the number of gates would be even? 。 How many times does a transition need to travel around the loop to bring the circuit back in its starting state? Develop a general formula to find the period and the frequency of the oscillation of the circuit as a function of the number of gates and the propagation delay of each gate 。 What would the expected oscillation period be for seven Schmitt trigger inverters? Adjust your circuit by adding two more inverters (name this tut2_task4b) and check whether the calculated time is correct. Make screenshots again. Follow all the submission requirements.

A step-up chopper is fed with 200 V. The conduction time of the thyristor is 200 µs and the required output is 600 V. If the frequency of operation is kept constant and the pulse width is halved, what will be the new output voltage?

Number 18 letters a, b and d.