PFD

Phase/frequency detector that compares phase and frequency between two signals

• Library:

• Mixed-Signal Blockset / PLL / Building Blocks

• 

Description

The PFD block produces two output pulses that differ in duty cycle. The difference in the duty cycle is proportional to the phase difference between input signals. In frequency synthesizer circuits, such as phase-locked loops (PLL), the PFD block compares the phase and frequency between the reference signal and signal generated by the VCO block and determines the phase error.

Ports

Input

reference — Reference frequency

scalar

Input port that transmits reference frequency to determine phase error.

Data Types: double

feedback — Feedback frequency

scalar

Output port that transmits the feedback frequency to determine the phase error. In a PLL system, the output of the VCO is fed back through feedback port to PFD after passing through a clock divider.

Data Types: double

Output

up — Transmits reference frequency

scalar

Output port that transmits reference frequency to Charge Pump to convert the phase error into current. The difference in the duty cycle of signals in up and down ports is proportional to the phase difference between the signals in reference and feedback ports.

Data Types: double

down — Transmits feedback frequency

scalar

Output port that transmits feedback frequency to Charge Pump to convert the phase error into current. The difference in the duty cycle of signals in up and down ports is proportional to the phase difference between the signals in reference and feedback ports.

Data Types: double

Parameters

Configuration

Deadband compensation (s) — Delay added for active output near zero phase offset

30e-12 (default) | positive real scalar

Delay added for active output near zero phase offset, specified as a positive real scalar in seconds. Deadband is the phase offset band near zero phase offset for which the PFD output is negligible.

Programmatic Use

• Use get_param(gcb,'DeadbandCompensation') to view the current value of Deadband compensation.

• Use set_param(gcb,'DeadbandCompensation',value) to set up Rise/fall time to a specific value.

Data Types: double

Enable increased buffer size — Enable increased buffer size

off (default) | on

Select to enable increased buffer size during simulation. This increases the buffer size of the Variable Pulse Delay, Logic Decision, and Slew Rate blocks inside the PFD block. By default, this option is deselected.

Buffer size — Number of samples of the input buffering available during simulation

10 (default) | positive integer scalar

Number of samples of the input buffering available during simulation, specified as a positive integer scalar. This sets the buffer size of the Variable Pulse Delay, Logic Decision, and Slew Rate blocks inside the PFD block.

Selecting different simulation solver or sampling strategies can change the number of input samples needed to produce an accurate output sample. Set the Buffer size to a large enough value so that the input buffer contains all the input samples required.

Dependencies

This parameter is only available when Enable increased buffer size option is selected in the Configuration tab.

Programmatic Use

• Use get_param(gcb,'NBuffer') to view the current value of Buffer size.

• Use set_param(gcb,'NBuffer',value) to set Buffer size to a specific value.

Data Types: double

Impairments

Enable impairments — Add circuit impairments to simulation

on (default) | off

Select to add circuit impairments such as rise/fall time and propagation delay to the simulation. By default, this option is selected.

Output step size calculation — Determine how output step size is calculated

Default (default) | Advanced

Determine how output step size is calculated:

• Select Default to calculate output step size from rise/fall time. Output step size (ΔT) is given by $$\Delta \text{T}=\frac{{\left(\text{Rise/fall time}\right)}^2}{6·\text{ 0}\text{.22}}$$.

• Select Advanced to calculate output step size from maximum frequency of interest. Output step size (ΔT) is given by $$\Delta \text{T}=\frac{\text{Rise/fall time}}{6·\text{ Maximum frequency of interest}}$$.

Dependencies

To enable this parameter, select Enable Impairments in the Impairments tab.

Maximum frequency of interest (Hz) — Maximum frequency of interest at output

10e9 (default) | positive real scalar

Maximum frequency of interest at the output, specified as a positive real scalar in Hz.

Dependencies

To enable this parameter, select Enable Impairments in the Impairments tab and choose Advanced for Output step size calculation.

Programmatic Use

• Use get_param(gcb,'MaxFreqInterest') to view the current value of Maximum frequency of interest (Hz).

• Use set_param(gcb,'MaxFreqInterest',value) to set Maximum frequency of interest (Hz) to a specific value.

Data Types: double

Rise/fall time (s) — 20% – 80% rise/fall time for up output port of PFD

3e-11 (default) | positive real scalar

20% – 80% rise/fall time for the up output port of the PFD, specified as a positive real scalar in seconds.

Dependencies

To enable this parameter, select Enable Impairments in the Impairments tab.

Programmatic Use

• Use get_param(gcb,'RiseFallTime') to view the current value of Rise/fall time (s).

• Use set_param(gcb,'RiseFallTime',value) to set Impairments to a specific value.

Data Types: double

Propagation Delay (s) — Delay from input port to output port of PFD

50e-12 (default) | positive real scalar

Delay from the input port to output port of the PFD, specified as a positive real scalar in seconds.

Dependencies

To enable this parameter, select Enable Impairments in the Impairments tab.

Programmatic Use

• Use get_param(gcb,'PropDelay') to view the current value of Propagation Delay (s).

• Use set_param(gcb,'PropDelay',value) to set Propagation Delay (s) to a specific value.

Data Types: double

More About

Inside the Mask

PFD consists of two D flip-flops in the master-slave configuration. The reference and feedback signals received at the corresponding ports act as the trigger. The outputs of the two flip-flops pass through a NAND gate, which acts as the reset signal. A pulse delay is introduced after the NAND gate using Variable Pulse Delay block to compensate for deadband.

The impairments are contained in variant subsystems and activated when impairments are enabled. The impairment subsystem utilized Slew Rate block to implement rise/fall time and propagation delay.

References

[1] Banerjee, Dean. PLL Performance, Simulation and Design. Indianapolis, IN: Dog Ear Publishing, 2006.