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
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-6 (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
Defaultto calculate output step size from rise/fall time. Output step size (ΔT) is given by .Select
Advancedto calculate output step size from maximum frequency of interest. Output step size (ΔT) is given by .
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
Rise/fall time (s) — 20%-80% rise/fall time for up input port
50e-12 (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.
Propagation delay — Total propagation delay for up input port
60e-12 (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.
Rise/fall time — 20%-80% rise/fall time for down input port
20e-12 (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.
Propagation delay — Total propagation delay for down input port
40e-12 (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,'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.