Clock Generator

Generate clock signal with one or more phases

Since R2022a

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Libraries:
Mixed-Signal Blockset / Utilities

Description

The Clock Generator block generates a clock signal with multiple output phases and detailed phase noise modeling. The signals at two output ports together model the output clock signal for each phase. These signals are: a saturated clock signal at the clock port and a clock transition time at the clockTime port.

You can use the block to model any clock recovery loop that uses a voltage controlled oscillator (VCO). The block consistently provides clock times where the noise floor is below –150 dBC/Hz. You can also use the block to include phase noise that matches a physical model.

Ports

Input

vctrl — Voltage to control output frequency

scalar | vector

Voltage to control the output frequency, specified as a scalar or vector.

Data Types: double

ReferenceOffset — Reference frequency offset

scalar

Offset for the reference frequency, specified as a scalar. If you select the ReferenceOffsetPort parameter, the ReferenceOffset port uses a reference offset value from an external block.

Data Types: double

PhaseOffset — Duty cycle phase offset

scalar

Offset for the duty cycle phase offset, specified as a scalar. If you select the PhaseOffsetPort parameter, the PhaseOffset port uses a phase offset value from an external block.

Data Types: double

Output

clock0 — Saturated output clock signal

scalar

Saturated output clock signal, returned as a scalar. There is one clock output port for each output phase.

clock0 is the default name of the port. The nonnegative scalar that follows the port name clock indicates the clock phase. For example, clock1 represents the saturated output clock signal for phase 1.

The output is a square wave whose amplitude is defined by the Output amplitude parameter.

Data Types: double

clockTime0 — Simulation time at last clock transition

scalar

Simulation time at the last clock transition, returned as a scalar. There is one clockTime output port for each output phase.

clockTime0 is the default name of the port. The nonnegative scalar that follows the port name clockTime indicates the clock phase. For example, clockTime1 represents the clock transition time for phase 1.

Data Types: double

Phase — Most recent clock phase of fundamental clock

scalar

Most recent clock phase of the fundamental clock, returned as a scalar.

Data Types: double

clockValid — Variable-step discrete-sampled clock

scalar

Variable-step discrete-sampled clock, specified as a scalar. The edge sample times of the signal at the clockValid port exactly match the values in the clock time signal.

Data Types: double

clockTime — Absolute clock time of most recent clock change

scalar

Absolute clock time of the most recent clock change at the clockValid port.

Data Types: double

Parameters

Main

Specify using — Define control sensitivity of clock generator

Voltage sensitivity (default) | Output frequency vs. control voltage | Period offset

Define control sensitivity of theclock generator.

• Select Voltage sensitivity to specify output frequency from the Voltage sensitivity (Hz/V) and Free running frequency (Hz) parameters.

• Select Output frequency vs. control voltage to interpolate output frequency from the Control voltage (V) vector versus the Output frequency (Hz) vector.

• Select Period offset to adjust the cycle time by the fraction of a nominal clock period. Use the Control voltage (V) parameter to specify the fraction. The block determines the values of the Voltage sensitivity (Hz/V) and Free running frequency (Hz) parameters using the value set in the Symbol time (s) parameter.

Programmatic Use

Block parameter: SpecifyUsing

Type: character vector

Values: Voltage sensitivity | Output frequency vs. control voltage | Period offset

Default: Voltage sensitivity

Voltage sensitivity (Hz/V) — Measure of change in output frequency

100e6 (default) | positive real scalar

Measure of change in output frequency for input voltage change, specified as a positive real scalar with units in Hz/V.

Programmatic Use

Block parameter: Kvco

Type: character vector

Values: positive real scalar

Default: 100e6

Data Types: double

Free running frequency (Hz) — Output frequency without control voltage

10e9 (default) | positive real scalar

Frequency of the clock generator without any control voltage input (0 V) or the quiescent frequency, specified as a positive real scalar in hertz.

Programmatic Use

Block parameter: Fo

Type: character vector

Values: positive real scalar

Default: 10e9

Data Types: double

Control voltage (V) — Control voltage values

[-5 0 5] (default) | real valued vector

Control voltage values of the clock generator, specified as a real valued vector in volts.

Programmatic Use

Block parameter: ControlVoltage

Type: character vector

Values: real valued vector

Default: [-5 0 5]

Data Types: double

Output frequency (Hz) — Clock generator output frequency values

[9.9e9 10e9 10.5e9] (default) | positive real valued vector

Output frequency of the clock generator corresponding to the Control voltage (V) vector, specified in hertz.

Programmatic Use

Block parameter: OutputFrequency

Type: character vector

Values: positive real valued vector

Default: [9.9e9 10e9 10.5e9]

Data Types: double

Output amplitude (V) — Maximum amplitude of clock generator output voltage

1 (default) | positive real scalar

Maximum amplitude of the clock generator output voltage, specified as a positive real scalar.

Programmatic Use

Block parameter: Amplitude

Type: character vector

Values: positive real scalar

Default: 1

Data Types: double

Phase unit — Units of output phase and duty cycle

Degrees (default) | Fraction of a clock cycle

The units of the output phase and duty cycle, specified as Degrees or Fraction of a clock cycle.

Programmatic Use

Block parameter: PhaseUnits

Type: character vector

Values: Degrees | Fraction of a clock cycle

Default: Degrees

Output phase — Phases of output clock signals

[0] (default) | nonnegative real scalar | nonnegative real valued vector

The phases of the output clock signals, specified as a scalar vector. If specified as a vector, each element defines one output.

Programmatic Use

Block parameter: OutputPhase

Type: character vector

Values: nonnegative real scalar | nonnegative real valued vector

Default: [0]

Output duty cycle — Duty cycle of the output clock signals

[180] (default) | positive real scalar | positive real valued vector

The duty cycles of the output clock signals, specified as a scalar or a vector. The clock output phase refers to the rising edge of the output clock.

If specified as a vector, each element defines one output. Missing or empty elements of the vector are given the default duty cycle. Extra elements are ignored.

The duty cycle must be greater than $$\frac{\text{Sample interval}}{\text{Symbol time}}$$ but less than $$1-\frac{\text{Sample interval}}{\text{Symbol time}}$$, defined as a fraction of clock cycle.

Programmatic Use

Block parameter: OutputDutyCycle

Type: character vector

Values: positive real scalar | positive real valued vector

Default: [180]

PhaseOffsetPort — Define duty cycle phase offset through an input port

on (default) | off

Define the duty cycle phase offset through PhaseOffset input port from an external block. If you deselect the PhaseOffsetPort parameter, it is removed from the AMI files. This effectively hard-codes phase offset to the value defined by the Phase offset (symbol time) parameter.

Phase offset (symbol time) — Duty cycle phase offset

0 (default) | scalar in the range [-0.5,0.5]

Duty cycle phase offset, specified as a scalar in the range [-0.5, 0.5] in fraction of symbol time. Phase offset manually shifts clock probability distribution function (PDF) for better bit error rate (BER)..

Dependencies

To enable this parameter, deselect PhaseOffsetPort.

Programmatic Use

Block parameter: PhaseOffset

Type: character vector

Values: scalar

Default: 0

ReferenceOffsetPort — Define reference frequency offset through an input port

on (default) | off

Define the reference frequency offset through ReferenceOffset input port from an external block. If you deselect the ReferenceOffsetPort parameter, it is removed from the AMI files. This effectively hard-codes Reference offset to the value defined by the Reference clock frequency offset (ppm) parameter.

Reference clock frequency offset (ppm) — Factor by which nominal output frequency is to be offset

0 (default) | scalar in the range of [-300,300]

The factor by which the nominal output frequency is to be offset from $$\frac{1}{\text{Symbol time}}$$, specified as a scalar in the range of [-300,300] in unit of parts per million. It is the deviation between the transmitter oscillator frequency and the receiver oscillator frequency

Dependencies

To enable this parameter, deselect ReferenceOffsetPort.

Programmatic Use

Block parameter: ReferenceOffset

Type: character vector

Values: scalar in the range of [-300,300]

Default: 0

Simulate using — Select simulation mode

Code generation (default) | Interpreted execution

Select the simulation mode. This choice affects the simulation performance.

Simulating the model using the Code generation method requires additional startup time, but the subsequent simulations run faster. Simulating the model using the Interpreted execution method may reduce the startup time, but the subsequent simulations run slower. For more information, see Interpreted Execution vs. Code Generation.

Programmatic Use

Block parameter: SimulateUsing

Type: character vector

Values: Code generation| Interpreted execution

Default: Code generation

Phase Noise

Add phase noise — Add phase noise as a function of frequency

on (default) | off

Select to introduce phase noise as a function of frequency. By default, this option is selected.

Phase noise frequency offset (Hz) — Frequency offsets of specified phase noise from carrier frequency

[30e3 100e3 1e6 3e6 10e6] (default) | positive real valued vector

The frequency offsets of the specified phase noise from the carrier frequency, specified as a positive real valued vector in hertz.

Dependencies

To enable this parameter, select Add phase noise in the Impairments tab.

Programmatic Use

Block parameter: Foffset

Type: character vector

Values: positive real valued vector

Default: [30e3 100e3 1e6 3e6 10e6]

Data Types: double

Phase noise level (dBc/Hz) — Specified phase noise power at phase noise frequency offsets relative to the carrier

[-56 -106 -132 -143 -152] (default) | negative real valued vector

The specified phase noise power in a 1 Hz bandwidth centered at the phase noise frequency offsets relative to the carrier, specified as a negative real valued vector in dBc/Hz. The elements of Phase noise level correspond to relative elements in the Phase noise frequency offset (Hz) parameter.

Dependencies

To enable this parameter, select Add phase noise in the Impairments tab.

Programmatic Use

Block parameter: PhaseNoise

Type: character vector

Values: negative real valued vector

Default: [-56 -106 -132 -143 -152]

Data Types: double

Estimate phase noise parameters — Estimate phase noise parameters from measured phase noise data

button

Click to estimate the phase noise parameters from the phase noise measured phase noise data. This calculates the Period jitter (S) and Flicker corner frequency (Hz) parameters from the Phase noise frequency offset (Hz) and Phase noise level (dBc/Hz) parameters. As a result, the phase noise profile matches a physical model.

Period jitter (S) — Standard deviation of period jitter

1.7e-15 (default) | positive real scalar

Standard deviation of the period jitter, specified as a positive real scalar in seconds. Period jitter is the deviation in cycle time of a clock signal with respect to the ideal period.

Programmatic Use

Block parameter: PeriodJitter

Type: character vector

Values: positive real scalar

Default: 1.7e-15

Flicker corner frequency (Hz) — Corner frequency of flicker noise

0 (default) | scalar

Corner frequency of the flicker noise, specified as a scalar in hertz. Flicker corner frequency (Hz) is defined as the frequency at which the phase noise transitions from 1/f² to 1/f³ due to flicker noise. At this frequency, the spectral densities of period jitter and flicker noise are equal.

Programmatic Use

Block parameter: CornerFrequency

Type: character vector

Values: scalar

Default: 0

Customize flicker exponent (Advanced feature) — Customize flicker noise power spectral distribution

off (default) | on

Select this parameter to customize the power spectral distribution of the flicker noise. Traditionally, flicker noise is defined as the 1/f noise, but it can vary as 1/f^V, where 0.8<V<1.5.

Flicker exponent — Flicker noise power exponent

1.0 (default) | 0.8 | 0.9 | 1.1 | 1.2 | 1.3 | 1.4 | 1.5

Flicker noise power exponent, specified between 0.8 to 1.5.

Programmatic Use

Block parameter: FlickerExponent

Type: character vector

Values: 1.0 | 0.8 | 0.9 | 1.1 | 1.2 | 1.3 | 1.4 | 1.5

Default: 1.0

Plot fit — Plot fitted phase noise profile

button

Click to plot the fitted phase noise profile. This allows you how the fitted model matches the specified phase noise data.

Advanced

Symbol time (s) — Time of single symbol duration

100e-12 (default) | real positive scalar

Time of a single symbol duration, specified as a real positive scalar in seconds.

Programmatic Use

Block parameter: SymbolTime

Type: character vector

Values: real positive scalar

Default: 100e-12

Data Types: double

Sample interval (s) — Uniform time step of waveform

6.25e-12 (default) | real positive scalar

Uniform time step of the waveform, specified as a real positive scalar in seconds.

Programmatic Use

Block parameter: SampleInterval

Type: character vector

Values: real positive scalar

Default: 6.25e-12

Data Types: double

Modulation (2:NRZ, 3:PAM3, 4:PAM4) — Modulation scheme

2 (default) | 3 | 4

Number of logic levels in the modulation scheme:

• Select 2 if the modulation scheme is NRZ(non-return to zero).

• Select 3 if the modulation scheme PAM3 (pulse amplitude modulation level 3).

• Select 4 if the modulation scheme PAM4 (pulse amplitude modulation level 4).

Programmatic Use

Block parameter: Modulation

Type: character vector

Values: 2.| 3 | 4

Default: 2

Data Types: char

Input waveform type — Type of input waveform

Sample (default) | Impulse

Type of input waveform, either a sample by sample signal or an impulse response signal.

Programmatic Use

Block parameter: WaveType

Type: character vector

Values: Sample.| Impulse

Default: Sample

More About

Clock and Data Recovery

To optimize clock and data recovery operation, specify the control sensitivity of the Clock Generator block using the Period offset option in the Specify using parameter. This maps the period offset input from the vctrl port to the center frequency and control sensitivity configuration. The voltage sensitivity is calculated for the currently configured symbol rate.

IBIS AMI Parameters

The reference offset and phase offset parameters are supported as IBIS-AMI parameters. You can define how they are included in the AMI files by using the PhaseOffsetPort and ReferenceOffsetPort.

Version History

Introduced in R2022a