Communications Blockset

Overview of PLL Simulation

A simple PLL consists of a phase detector, a loop filter, and a voltage-controlled oscillator (VCO). For example, the following figure shows how these components are arranged for an analog passband PLL. In this case, the phase detector is just a multiplier. The signal e(t) is often called the error signal.

Different PLLs use different phase detectors, filters, and VCO characteristics. Some of these attributes are built into the PLL blocks in this blockset, while others depend on parameters that you set in the block mask:

• You specify the filter's transfer function in the block mask using the Lowpass filter numerator and Lowpass filter denominator parameters. Each of these parameters is a vector that lists the coefficients of the respective polynomial in order of descending exponents of the variable s. To design a filter, you can use functions such as butter, cheby1, and cheby2 in the Signal Processing Toolbox.
• You specify the key VCO characteristics in the block mask. All four PLL blocks use a VCO input sensitivity parameter. Some blocks also use VCO quiescent frequency, VCO initial phase, and VCO output amplitude parameters.
• The phase detector for each of the PLL blocks is a feature that you cannot change from the block mask.

Synchronization

Implementing an Analog Baseband PLL