DAC AC Measurement

Measure AC performance metrics of DAC output

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  • DAC AC Measurement block

Libraries:
Mixed-Signal Blockset / DAC / Measurements & Testbenches

Description

The DAC AC Measurement block measures DAC AC performance metrics such as signal-to-noise ratio (SNR), signal to noise and distortion radio (SINAD), spurious-free dynamic range (SFDR), effective number of bits (ENOB), and noise floor. You can use DAC AC Measurement block to validate the DAC architecture models provided in Mixed-Signal Blockset™, or you can use a DAC of your own implementation

Examples

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Open Model

This example shows how to find the AC performance metrics such as SNR, SINAD, SFDR, ENOB, and noise floor using a DAC AC Measurement block.

Open the model dac_ac_measure. The model consists of a Signal Generator, a Flash ADC, a Binary Weighted DAC block, and a DAC AC Measurement block.

model = 'dac_ac_measure';
open_system(model)

The Flash ADC acts as the input to the Binary Weighted DAC. The ADC uses an internal start clock whose Conversion start frequency (Hz) is 1e6 and RMS aperture jitter (s) is 1e-12. The input analog frequency to the Flash ADC from the Signal Generator is 250.98 kHz.

The Number of bits of the Binary Weighted DAC is set to 10. All other parameters are kept at their default values.

The Digital signal frequency (Hz) of the DAC AC Measurement block is 2.5098e5 and the Start conversion frequency (Hz) is 1e6.

Run the simulation for 0.0003586 s.

sim(model);

The measured AC performance metrics are displayed on the DAC AC Measurement block.

Ports

Input

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Digital input signal from a DAC, specified as a scalar.

Data Types: fixed point | single | double | int8 | int16 | int32 | uint8 | uint16 | uint32

Converted analog signal from a DAC, specified as a scalar.

Data Types: double

External clock to start conversion, specified as a scalar. This port determines when digital-to-analog conversion process starts.

Data Types: double

Parameters

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Frequency of the digital input signal to the DAC block, specified as a positive real scalar in hertz. Digital signal frequency (Hz) must match the input frequency of the DAC device under test.

Digital input frequency (Hz) needs to satisfy two requirements:

  • All the output codes of the DAC must be activated.

  • The Digital signal frequency (Hz) must not share any common multiples other than 1 with the Conversion start frequency (Hz).

Programmatic Use

Block parameter: InputFrequency
Type: character vector
Values: positive real scalar
Default: 1e3

Data Types: double

Frequency of the internal start conversion clock, specified as a real scalar in Hz. The Start conversion frequency parameter determines the conversion rate at the start of conversion.

Programmatic Use

Block parameter: StartFreq
Type: character vector
Values: positive real scalar
Default: 1e6

Data Types: double

The tolerance allowed for calculating settling time, specified as a positive real scalar in LSB. The output of the DAC must settle within the Settling time tolerance (LSB) by Settling time (s).

Programmatic Use

Block parameter: SettlingTimeTolerance
Type: character vector
Values: positive real scalar
Default: 0.5

Data Types: double

Delay before measurement analysis to avoid corruption by transients, specified as a nonnegative real scalar in seconds.

Programmatic Use

Block parameter: HoldOffTime
Type: character vector
Values: nonnegative real scalar
Default: 0

Minimum time the simulation must run to obtain meaningful results, specified as a positive real scalar in seconds.

To measure AC performance, the simulation must run so that the DAC can generate six spectral updates of the DAC output. So, the Recommended simulation stop time (s) T is given by [1]:

T=6(1.5RBW+Hold off time),

where RBW is the resolution bandwidth of the spectrum estimator inside the DAC Testbench block and is given by the equation: RBW=[min(Input frequency)0.1].

This parameter is only reported by the block and is not editable.

Data Types: double

Store detailed test results to a struct in the base workspace for further processing at the end of simulation. By default, this parameter is deselected.

Name of the variable that stores detailed test results, specified as a character string.

Dependencies

To enable this parameter, select Output result to base workspace parameter.

Programmatic Use

Block parameter: VariableName
Type: character vector
Values: character string
Default: dac_ac_out

Select this parameter to display the Spectrum Analyzer window during simulation. By default, this parameter is selected.

More About

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References

Version History

Introduced in R2020a

See Also

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