- on Computers & microprocessors
- Published in issue 7/1989 on page 30
Hcmos Square Wave Generator
046 HCMOS SQUARE WAVE GENERATOR This pulse generator supplies three rectangular output signals with a duty factor of 0.5. The signals have a fixed phase relation to one another: output 3 is the reference; output 2 has a phase shift of about 180 0; and output 1 has a phase shift of about 10 ¬∞. The generator is formed by the four bi-direction- al HCMOS electronic switches contained in a Type 74HC4066 lc. Its operation is based on the fairly accurately defined switching threshold of an Hcmos input. The toggle point for low and high levels lies around Lib /2 to ensure a duty factor of 0.5 and thus a square wave output signal. When the supply is switched on, Cl is charged via R3 and the on-resistance of ES3. When the volt- age of Cl reaches Ub/2, ES4 closes and pulls the control input of ES3 low, causing Cl to discharge via ES2 and R3. When the "low" switching threshold is reached at the control input of ES4, the generator starts to oscillate. Considering the oscillator is basically a...