Microcontroller controls analog phase shifter
By using a digital potentiometer in a phase-shift circuit, a microcontroller can precisely control phase shift.
Nick Ierfino, IGS Technologies, Montreal, PQ, Canada; Edited by Charles H Small and Fran Granville -- EDN, June 12, 2008
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 1/(2×π×R×C). 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.
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Hello!
Could you please provide waveform of the produced signal?
Also how the output signal is measured in order to verify the parameters?
More information about the PLL applications, if possible?
BR
Petre Petrov
Petre Petrov - 2008-30-12 02:26:00 PST -
It would be nice to have a little more information as to what you are actually telling the 16F84 to do!?
Chuck Irwin - 2008-11-9 12:22:00 PDT -
By my calculations the phase varies once, from 0 to -180, if one considers the resistance range of 0 to infinity.
Also worth a comment is that the signal needs to be offset from ground due to input limits of the resistor chip.
Nick Allen - 2008-20-6 13:29:00 PDT
