Charge Pump

Output a current proportional to the difference in duty cycle between two input ports

• Library:

• Mixed-Signal Blockset / PLL / Building Blocks

• 

Description

The Charge Pump block produces an output current which is proportional to the difference in duty cycles between the signals at its up and down input ports. In a phase-locked loop (PLL) system, the Charge Pump block converts the phase error as represented by the two outputs of the PFD block into a single current at the input to the Loop Filter.

Ports

Input

up — Input port

scalar

Input port, connected to the up output of a PFD in a PLL system.

Data Types: double

down — Input port

scalar

Input port, connected to the down output of PFD in a PLL system.

Data Types: double

Output

out — Output port

scalar

Output port, connected to the Loop Filter block in a PLL system. out delivers current proportional to the difference in duty cycles between up and down input ports.

Data Types: double

Parameters

Configuration

Output current (A) — Design output current

1e-3 (default) | positive real scalar

Full scale magnitude of design output current, specified as a positive real scalar in amperes.

Programmatic Use

• Use get_param(gcb,'OutputCurrent') to view the current value of Output current (A).

• Use set_param(gcb,'OutputCurrent',value) to set Output current (A) to a specific value.

Input threshold (V) — Logic switching threshold at input ports

0.5 (default) | real scalar

Logic switching threshold at input ports, specified as a real scalar in volts.

Programmatic Use

• Use get_param(gcb,'InputThreshold') to view the current value of Input threshold (V).

• Use set_param(gcb,'InputThreshold',value) to set Input threshold (V) to a specific value.

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 Logic Decision and Slew Rate inside the Charge Pump 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 Logic Decision and Slew Rate inside the Charge Pump 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.

Impairments

Enable current impairments — Add current impairments to simulation

on (default) | off

Select to add current impairments such as current imbalance and leakage current to simulation. By default, this option is selected.

Current imbalance (A) — Difference between full scale positive and negative current

1e-7 (default) | positive real scalar

Difference between full scale positive and negative current, specified as a positive real scalar in amperes.

Dependencies

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

Programmatic Use

• Use get_param(gcb,'CurrentImbalance') to view the current value of Current imbalance (A).

• Use set_param(gcb,'CurrentImbalance',value) to set Current imbalance (A) to a specific value.

Data Types: double

Leakage current (A) — Output current without any input

1e-8 (default) | nonnegative real scalar

Output current when both inputs are at logic zero, specified as a nonnegative real scalar in amperes.

Dependencies

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

Programmatic Use

• Use get_param(gcb,'LeakageCurrent') to view the current value of Leakage current (A).

• Use set_param(gcb,'LeakageCurrent',value) to set Leakage current (A) to a specific value.

Data Types: double

Enable timing impairments — Add timing impairments to simulation

on (default) | off

Select to add timing impairments such as rise/fall time and propagation delay to 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 timing 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 timing 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

up

Rise/fall time (s) — 20%-80% rise/fall time for up input port

5e-9 (default) | positive real scalar

20%-80% rise/fall time for up input port, specified as a positive real scalar in seconds.

Dependencies

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

Programmatic Use

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

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

Up propagation delay — Total propagation delay for up input port

6e-9 (default) | positive real scalar

Total propagation delay for up input port, 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,'PropDelayUp') to view the current value of Up propagation delay.

• Use set_param(gcb,'PropDelayUp',value) to set Up propagation delay to a specific value.

down

Rise/fall time — 20%-80% rise/fall time for down input port

2e-9 (default) | positive real scalar

20%-80% rise/fall time for down input port, 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,'RiseFallDown') to view the current value of down Rise/fall time.

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

Down propagation delay — Total propagation delay for down input port

4e-9 (default) | positive real scalar

Total propagation delay for down input port, 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,'PropDelayDown') to view the current value of Down propagation delay.

• Use set_param(gcb,'PropDelayDown',value) to set Down propagation delay to a specific value.

More About

Inside the Charge Pump

The Charge Pump block converts the two outputs of the PFD block into a single output. It consists of two current branches: one Up and one down. The difference between these two branches is summed to the leakage current impairment, if enabled.

Each current branch consists of a Logic Decision block, an Impairments subsystem, and a gain block. The Logic Decision block compares the incoming signal to the Input Threshold. The Impairments subsystem incorporates the effect of the charge pump impairments. The gain block multiplies the output of the Impairments subsystem to produce the current level defined in the Output current parameter.

References

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

[2] Gardner, Floyd M. Phaselock Techniques. Hoboken, NJ: John Wiley & Sons, Inc. 2005.

Version History

Introduced in R2019a