5.22  A ring oscillator is a circuit that has an odd number, n, of inverters connected in a ringlike structure, as shown in Figure P5.5. The output of each inverter is a periodic signal with a certain period.

 

 

f

 

 

 

Figure P5.5   A ring oscillator.

 

 

(a)    Assume that all the inverters are identical; hence they all have the same delay, called tp. Let the output of one of the inverters be named f . Give an equation that expresses the period of the signal f in terms of n and tp.

(b)    For this part you are to design a circuit that can be used to experimentally measure the delay tp through one of the inverters in the ring oscillator. Assume the existence of an input called Reset and another called Interval. The timing of these two signals is shown in Figure P5.6. The length of time for which Interval has the value 1 is known. Assume that this length of time is 100 ns. Design a circuit that uses the Reset and Interval signals and the signal f from part (a) to experimentally measure tp. In your design you may use logic gates and subcircuits such as adders, flip-flops, counters, registers, and so on.

 

 

Reset

 

 

 

Interval

 

 

                            100 ns                             

 

 

Figure P5.6   Timing of signals for Problem 5.24.