Prescaler

From Wikipedia, the free encyclopedia

A prescaler is an electronic device that takes a frequency and reduces it by a pre-determined factor. For example; converts a 1 MHz signal to a 100kHz signal (scales the frequency by a factor of 10).

[edit] Example of use

There are many applications for prescalers. An example is in conjunction with Phase-locked loops (PLL) in transmitters. A PLL supplies a voltage to a Voltage-controlled oscillator (VCO). This voltage causes the frequency (freq) to increase or decrease.

A prescaler can convert a transmission frequency of 1.1GHz (microwave radio communications) to 1.1kHz. This scaled signal is then 'mixed' with the output of a local oscillator (LO). Any difference in these two nominally identical frequencies will be converted into an error voltage. It is this which is fed into a PLL.

If the difference is 0, the PLL will generate an 'error' voltage of 0, with no change to the output of the transmitter. If the error voltage is non-zero, the frequency adjusts up or down accordingly, and your transmitter remains fixed on the one same frequency. Radios work in a similar fashion.

Although it would be possible in principle for the phase-locked loop to operate at the higher frequency, in practice it is can be substantially easier to design circuits that function at the lower frequency. Avalailability of crystal oscillators might also be problematic.

Prescalers are an essential part of modern electronics.