In this post we discuss a simple yet extremely stable CMOS square wave generator circuit whose output can be controlled ON/OFF through an external high/low signal.
In electronic digital circuits in which parallel data needs to be transformed into serial data, a start-stop oscillator is usually employed. One particular strategy is to utilize the oscillator to pulse a counter, whose output is analyzed with the parallel data.
At first the counter is set to default position; next the external oscillator is switched ON, sending the clock pulses to the counter; as soon as the right count is attained, the oscillator is switched OFF.
By doing this a (clock) pulse sequence, having a length of equivalent to the binary number specified by the parallel data.
This may not be adequate for these applications to clock the output of a free-running oscillator, considering that the 'enable' signal may not be typically aligned with the oscillator.
The stable square wave generator circuit detailed above is in fact switched on and off through the enable signal, it has proved very well-performing and stable for output frequencies ranging up to 10 MHz.
Provided that the enable input (one input of N3) is held at logic 0, the oscillator working will be inhibited and the output of N4 is likewise kept at logic 0.
Once the enable input turns into logic 1, the square wave oscillator begins working instantly and the initial output pulse is delayed only through the propagation periods of N3 and N4.