EE 322

Phase-Locked Loops (PLL's) and PM Demodulation

The purpose of this lab is to use a phased-locked loop circuit to implement a simple demodulator for frequency modulated signals.

Use two 4046 chips in this lab, the first will produce a FM signal using only the VCO portion of the chip. The second will be a PLL to demodulate the signal.

WARNING -- there are two different chips in the lab, 4046A and 4046B. Use the 4046A. They are different and require different Rs and Cs. There is a data sheet for each.

Voltage-Controlled Oscillator

Phased-locked loops are available in integrated-circuit packages which contain a phase-detector and a VCO. The PLL we will use in the lab is the popular 4046. The VCO frequency range for the 4046 is determined by two external resistors and an external capacitor. The discussion on the 4046 in the correct data sheet shows how to select values for these components.

Phased-Locked Loop

To use the PLL as a demodulator, we need to finish the PLL by adding the phase detector and low-pass filter. The 4046 has three different phase detectors, as discussed in the data book. For this experiment, we will use the Type~1 detector. We will also use a simple RC filter as the low-pass filter, as discussed in class.

PM demodulation

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