CMOS Oscillators INTRODUCTION This note describes several square wave oscillators that can be built using CMOS logic elements. These circuits offer the following advantages: Guaranteed startability Relatively good stability with respect to power supply variations Operation over a wide supply voltage range (3V to 15V) Operation over a wide frequency range from less than 1 Hz to about 15 MHz Low power consumption Easy interface to other logic families and elements in- cluding TTL Several RC oscillators and two crystal controlled oscillators are described. The stability of the RC oscillator will be suffi- cient for the bulk of applications; however, some applications will probably require the stability of a crystal. Some applica- tions that require a lot of stability are: 1. Timekeeping over a long interval. A good deal of stability is required to duplicate the performance of an ordinary wrist watch (about 12 ppm). This is, of course, obtain- able with a crystal. However, if the time interval is short and/or the resolution of the timekeeping device is rela- tively large, an RC oscillator may be adequate. For ex- ample: if a stopwatch is built with a resolution of tenths of seconds and the longest interval of interest is two min- utes, then an accuracy of 1 part in 1200 (2 minutes x 60 seconds/minute x 10 tenth/second) may be acceptable since any error is less than the resolution of the device. 2. When logic elements are operated near their specified limits