Communications Blockset

Linearized Baseband PLL

Implement a linearized version of a baseband phase-locked loop

Library

Synchronization

Description

The Linearized Baseband PLL block is a feedback control system that automatically adjusts the phase of a locally generated signal to match the phase of an input signal. Unlike the Phase-Locked Loop block, this block uses a baseband model method. Unlike the Baseband PLL block, which uses a nonlinear model, this block simplifies the computations by using x to approximate sin(x). The baseband PLL model depends on the amplitude of the incoming signal but does not depend on a carrier frequency.

This PLL has these three components:

• An integrator used as a phase detector.
• A filter. You specify the filter's transfer function using the Lowpass filter numerator and Lowpass filter denominator mask parameters. Each is a vector that gives the respective polynomial's coefficients in order of descending powers of s.

• To design a filter, you can use functions such as butter, cheby1, and cheby2 in the Signal Processing Toolbox. The default filter is a Chebyshev type II filter whose transfer function arises from the command below.

  [num, den] = cheby2(3,40,100,'s')

• A voltage-controlled oscillator (VCO). You specify the sensitivity of the VCO signal to its input using the VCO input sensitivity parameter. This parameter, measured in Hertz per volt, is a scale factor that determines how much the VCO shifts from its quiescent frequency.

The input signal represents the received signal. The input must be a sample-based scalar signal. The three output ports produce:

• The output of the filter
• The output of the phase detector
• The output of the VCO

Dialog Box

Lowpass filter numerator

The numerator of the lowpass filter's transfer function, represented as a vector that lists the coefficients in order of descending powers of s.

Lowpass filter denominator

The denominator of the lowpass filter's transfer function, represented as a vector that lists the coefficients in order of descending powers of s.

VCO input sensitivity (Hz/V)

This value scales the input to the VCO and, consequently, the shift from the VCO's quiescent frequency.

See Also

Baseband PLL, Phase-Locked Loop

References

For more information about phase-locked loops, see the works listed in Selected Bibliography for Synchronization in Using the Communications Blockset.

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