Quartz crystal oscillator circuit using C-MOS converter

Quartz crystal oscillator circuit using C-MOS converter

Function of the circuit

Recently, there is a trend to replace TTL devices with C-MOS devices, and the 74HC series products have been further enriched. The clock oscillation circuit composed of 2-level TTL can be replaced by the oscillation circuit composed of C-MOS IC, because if the parameters of TTL IC components such as bias resistors are not properly selected, it is easy to stop oscillation or produce abnormalities, but this circuit can be simply constructed and oscillate accurately.

How the Circuit Works

In order to make the C-MOS conversion work in the online linear state, the self-bias resistor R1 is connected between the input and output terminals to fix the input terminal at the threshold voltage. If the high-speed C-MOS is directly used as an oscillation circuit, abnormal oscillation is likely to occur, so a resistor of several K is connected in series with the quartz oscillator, and a low-pass filter is formed by the capacitor C2.

The oscillation frequency is adjusted by the capacitor connected to the input terminal of C-MOS. If accurate adjustment is required, the fine-tuning capacitor VC1 can be used for fine-tuning.

This circuit can be used as a wide-band quartz crystal oscillator circuit. The capacity of the parallel capacitors C1 and C2 should be selected according to the oscillation frequency. According to the parameters in the figure, the oscillation frequency is 2~20MHZ.

4000 series C-MOS devices can also be used, but when VDD=5V, the conversion speed is slow and the oscillation frequency can only reach a few MHZ.