Digital Three-Phase Sinewave Generator

Generating three sinewave signals with constant relative phase offsets of 120 degrees using analogue circuitry is not always easy, especially if it is desired to cover a wide frequency range. The circuit shown here solves this problem in a digital manner, which yields a frequency range of nearly 0 Hz to more than 100 MHz with a fully constant phase offset of 120 degrees. Furthermore, it costs only a couple of pounds to build.The heart of the circuit shown in Figure 1 is formed by IC2, which is an 8-bit shift register wired as a 6-bit Johnson counter. A Johnson counter does not simply count directly from zero to the maximum possible count in equal increments, but instead jumps around from one count to the next in a more or less complicated manner.