MAKE THE PLL FREQENCY SYNTHESIZER WITH PIC CONTROL

摘要

A frequency synthesizer (signal generator) is a device which generates a very stable waveform at a user-selected frequency. They are very handy when you need such a waveform as an input to another circuit such as an audio mixer, a radio transmitter, or digital logic. This design is optimized for use with digital circuits but can easily be adapted to audio or radio frequency applications. The short list of requirements I had for this synthesizer included a wide frequency range (up to 30 MHz), small frequency steps (1 kHz), high accuracy, 50% duty cycle output, and a simple user interface for selecting the frequency. The end result (Figure 1) met all these requirements at a cost of around $70 including the custom-made circuit board. There are some ready-made synthesizer chips on the market including the LTC6904 - a neat little eight-pin device with an I~2C interface - but these didn't have the frequency steps I wanted or had insufficient accuracy.