Microcontroller Controlled Analog Phase Shifter

Phase shifters are widely used in various circuits, but due to the deviation in the amplifier and the tolerance of the capacitors, it is usually difficult to achieve the precise phase shift required for accurate control of the circuit. The circuit in Figure 1 uses the AD5227 64-step up/down digital potentiometer IC3 to control the phase shift from input to output and replace the resistor value. The formula for calculating the output center frequency is: FCENTER = 1/(2×π×R×C). The AD5227 can take a variety of different ranges of resistor values. The resistor in this example is 10kΩ. By stepping 64 points, the 720kHz input sine wave can cycle from 0 degrees to 360 degrees several times. The AD5227 acts as a potentiometer, with A and B as the two ends and W as the wiper.

This example uses a PIC16F84 microcontroller IC2 with a 20MHz crystal frequency. This microcontroller has a theoretical potential performance of 5MIPS and can be used for many purposes in a phase-locked loop (PLL) circuit. The AD5227 can also be controlled by any microcontroller, even a field programmable gate array (FPGA).