Symmetrical cascode oscillator

by R Shankar 14symmetrical cascode oscillator Free running as well as crystal con- trolled clock generators in many digital designs are most frequently based upon the use of one or more inverter gates. However easy it may seem to use these devices for the construction of reliable oscillators, the resultant frequency stability is generally not such as might be ex- pected from a look at the relevant quartz crystal data, and this is mainly on account of the rather poorly de- fined capacitive and/or inductive loading of the crystal at resonance. Stability, however, may be improved by a factor 3 to 5 by using cascode type inverters in a symmetrical con- figuration, as can be seen in the ac- companying circuit diagram. Two sets of two n- and p-channel MOS- FETs, contained in the Type 4007UB IC, have been connected to form a highly stable oscillator circuit capable of operation at frequencies up to 10 MHz, as determined by quartz crystal Xi, which should be a series resonant type. As the...