HCMOS VCO

59HCMOS VCO Crafty designers are forever trying to use ICs for applications they were never intended for. In this circuit a member of the newish HCMOS fam- ily is used as a voltage-controlled oscillator (VCO). This is achieved by using the characteristic of the HCMOS family of operating from a 2 to 6 volt supply. However, at 6 V these ICs are faster than at 2 V. In the present circuit, a "supply voltage" variable between 1.5 and 5 V is used as the input signal of the oscillator, which consists of three cascaded NAND gates. The VCO operates as follows: a logic 1 at pin 2 causes a logic 0 at pin 3; this becomes a 1 at pin 6, and a 0 at pin 8. Pin 8 is, however, connected to pin 2, which, therefore, is no longer 1 but becomes 0. This 0, because of the delay times of the gates, appears a little later at pin 2 as a logic 1. And so on: the oscillator works! Gate N4 functions as a buffer for the oscillator output. Since the peak output voltage cannot be greater than the supply voltage, i...