Phase shifters are widely used in various circuits. However, due to the deviation and capacitance tolerance in amplifiers, it is difficult to achieve the precise phase shift required for precise control of circuits. The circuit in the figure uses ad5227 64 step increment / decrement digital potentiometer IC3 to control the phase shift from input to output and replace the resistance value. The formula for calculating the output center frequency is: fcenter = 1 / (2 & times; π& TImes; R&TImes; C）。 Ad5227 can take a variety of different ranges of resistance values. The resistance in this example is 10K Ω。 By stepping 64 points, the 720khz input sine wave can cycle from 0 to 360 degrees several times. Ad5227 as a potentiometer, a and B for both ends, w for wiper.
Figure 1 pic16f84 sets the resistance of ad5227 digital potentiometer to precisely control the output phase shift of analog input
In this example, pic16f84 microcontroller IC2 with 20MHz crystal frequency is applied. The theoretical potential performance of the microcontroller is 5mips, which can be used in many applications in PLL circuit. Ad5227 can also be controlled by any microcontroller or even a field programmable gate array (FPGA).