Phase shifters find use in a variety of circuits, but variation in amplifier and capacitance tolerances usually makes it difficult to control the exact phase shift that precise control circuitry requires. The circuit in Figure 1 can control the phase shift from input to output by using IC3, an AD5227 64-step-up/step-down control digital potentiometer, to replace the value for the resistance. The formula of the center frequency of the output is
|Figure 1.||A PIC16F84 sets the resistance of the AD5227 digital potentiometer, precisely controlling the phase shift of
the output with respect to the analog input.
Different ranges of resistance are available for the AD5227. This example uses a 10-kΩ value. By stepping through the 64 points, the 720-kHz input sine wave rotates several times from 0 to 360°. The AD5227 acts as a potentiometer, in which A and B are the extremes and W is the wiper.
This example uses IC2, a PIC16F84 microcontroller with a crystal frequency of 20 MHz. This microcontroller has a theoretical potential performance of 5 MIPS and should serve many purposes in PLL (phase-locked-loop) circuitry. You could use any microcontroller or even an FPGA to control the AD5227.