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ADC Testbench

Measures DC and AC performance metrics of ADC output

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  • ADC Testbench block

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

Description

The ADC Testbench block measures both DC and AC performance metrics. DC performance metrics include offset error and gain error. AC performance metrics include signal to noise ratio (SNR), signal to noise and distortion ratio (SINAD), spurious free dynamic range (SFDR), effective number of bits (ENOB), noise floor, and conversion delay.

The ADC Testbench block generates the stimulus to drive the device under test (DUT) from the Stimulus tab. The setup parameters for validating the DUT are defined in the Setup tab and the target validation metrics are defined in the Target Metric tab.

You can use the ADC Testbench block to validate the ADC architectural models provided in Mixed-Signal Blockset™, or you can validate an ADC of your own implementation.

Ports

Input

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Digital input signal from the ADC output, specified as a scalar.

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

Conversion ready signal from the ADC output, specified as a scalar. This signal indicates when the ADC conversion process is complete.

Data Types: double

Output

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Analog output stimulus signal for the ADC input, returned as a scalar.

Data Types: double

External start conversion clock for ADC, returned as a scalar. The rising edge of this signal starts the conversion process in ADC block.

Data Types: double

Parameters

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Select whether to measure static (DC) or dynamic (AC) performance metrics.

  • Select DC to measure offset error and gain error.

  • Select AC to measure SNR, SINAD, SFDR, ENOB, noise floor, and conversion delay.

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

  • To measure DC performance, the simulation must run so that ADC can sample each digital code 10 times, assuming a ramp input that traverses the full scale range of the ADC over the period of simulation. Based on this assumption and considering that the maximum allowed error tolerance is 0.1, the analog input frequency (fanalog), generated by the ADC Testbench block for the sawtooth waveform is set as:

    fanalog=StartFreq·min(ErrorTolerance,0.1)2(Nbits+1)

    where StartFreq is the frequency of the conversion start clock and Nbits is the resolution of the ADC.

    So, the Recommended min. simulation stop time (s) T is calculated by using the formula: T=1fanalog+HoldOffTime.

  • To measure AC performance, the simulation must run so that the ADC can generate 6 spectral updates of the ADC output. The time to generate one spectral output based on Welch's method is given by:

    t=1.5·SamplingFrequencyRBW

    where SamplingFrequency and RBW are the sampling frequency and resolution bandwidth of the spectrum estimator inside the ADC Testbench block.

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

Data Types: double

Click to automatically set the Recommended min. simulation stop time (s) as the stop time of the Simulink® model.

Measure the differential nonlinearity (DNL) error and integral nonlinearity (INL) error using the endpoint method. This method uses the end points of the actual transfer function to measure the DNL and INL error.

Measure the differential nonlinearity (DNL) error and integral nonlinearity (INL) error using the best fit method. This method uses a standard curve fitting technique to find the best fit to measure the DNL and INL error.

Click to plot DC analysis result for further analysis. To perform a complete DC analysis including integral nonlinearity (INL) and differential nonlinearity (DNL), use the ADC DC Measurement block.

Dependencies

This parameter is only available when Measurement option is set to DC.

Click to store detailed test results to a spreadsheet (XLS file) or as comma-separated values (CSV file) for further processing.

Stimulus

Rate at which the ADC Testbench block polls its input, specified as a positive real scalar in seconds. The testbench reads the input signal and updates the value of its output to control the device under test.

Dependencies

To enable this parameter, set Measurement option as DC.

Programmatic Use

Block parameter: SampleInterval
Type: character vector
Values: positive real scalar
Default: 1e-6

Type of distortion the ADC Testbench block is set to measure, specified as Harmonic or Intermodulation.

If the block is calculating the Analog stimulus frequency automatically,

  • when measuring harmonic distortion, the calculated stimulus frequency is used directly.

  • when measuring intermodulation distortion, the harmonics are chosen as one tenth above and below the calculated stimulus frequency.

Dependencies

To enable this parameter, set Measurement option as AC.

Programmatic Use

Block parameter: DistortionMeasurement
Type: character vector
Values: Harmonic | Intermodulation
Default: Harmonic

Frequency of the analog input signal to an ADC block, specified as a positive real scalar in hertz. Analog stimulus frequency must match the input frequency to the ADC device under test. By default, this parameter is calculated automatically. You can deselect Set automatically to customize the value.

If the block is calculating the Analog stimulus frequency automatically,

  • when measuring harmonic distortion, the calculated stimulus frequency is used directly.

  • when measuring intermodulation distortion, the harmonics are chosen as one tenth above and below the calculated stimulus frequency.

Analog stimulus frequency must not share any common multiples other than 1 with the Start conversion frequency.

To satisfy this condition, use the equation fanalog=JMfstart,

where:

fanalog is the analog signal frequency,

fstart is the start conversion frequency,

J is the number of cycles of the stimulus per FFT window,

and M is the number of FFT points.

Note

J is selected as the largest prime number less than one tenth of the number of FFT points. The minimum value of M is allowed to be 16.

Dependencies

To enable this parameter, set Measurement option as AC.

Programmatic Use

Block parameter: InputFrequency
Type: character vector
Values: positive real scalar | positive real valued vector
Default: 98632.8125

Resolution bandwidth, specified as a positive real scalar in hertz. This parameter defines the smallest positive frequency that can be resolved. By default, this parameter is calculated automatically. You can deselect Set automatically to customize the value.

Dependencies

To enable this parameter, set Measurement option as AC.

Programmatic Use

Block parameter: RBW
Type: character vector
Values: positive real scalar
Default: 976.5625

Frequency of the start conversion clock of the ADC, specified as a positive real scalar in Hz. Start conversion frequency (Hz) must match the frequency of the start conversion clock of the ADC block.

Programmatic Use

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

Data Types: double

RMS aperture jitter to be added by the start conversion clock, specified as a positive real scalar in seconds.

Programmatic Use

Block parameter: RMSJitt
Type: character vector
Values: positive real scalar
Default: 40e-12

Data Types: double

Maximum allowed difference in the amplitude of the successive samples of the analog input signal, specified as positive real scalar in least significant bit (LSB).

Dependencies

To enable this parameter, set Measurement option as DC.

Data Types: double

Select to automatically determine the sweep range from the ADC dynamic input range and target metrics. You can deselect this option to specify a custom sweep range.

Dependencies

To enable this parameter, set Measurement option as DC.

Define a custom sweep range, specified as a 2-element vector.

Dependencies

To enable this parameter, set Measurement option as DC and deselect the Automatically determine sweep range parameter.

Data Types: double

Select to stop the simulation on completion. You can deselect this option terminate a simulation early.

Dependencies

To enable this parameter, set Measurement option as DC.

Setup

Click to automatically propagate setup parameters from the ADC.

Dependencies

This parameter only works when the ADC is a Flash ADC or a SAR ADC from the Mixed-Signal Blockset.

Number of physical output bits, specified as a unitless positive real integer in the range [1, 26]. Number of bits determines the resolution of the ADC.

Programmatic Use

  • Use get_param(gcb,'NBits') to view the current Number of bits.

  • Use set_param(gcb,'NBits',value) to set Number of bits to a specific value.

Data Types: double

ADC dynamic range, specified as a 2-element row vector in volts.

Programmatic Use

Block parameter: InputRange
Type: character vector
Values: 2-element row vector
Default: [-1 1]

Data Types: double

Delays 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

Data Types: double

Displays spectrum analyzer during simulation. By default, this option is deselected.

Dependencies

This parameter is only available when Measurement option is set to AC.

Select to enable increased buffer size during simulation. By default, this option is deselected.

Number of samples of the input buffering available during simulation, specified as a positive integer scalar.

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 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

Block parameter: NBuffer
Type: character vector
Values: positive integer scalar
Default: 5

Data Types: double

Target Metric

Click to automatically propagate target metrics from ADC.

Dependencies

  • To enable this parameter, set Measurement option to DC.

  • This parameter only works when the ADC is a Flash ADC or a SAR ADC from the Mixed-Signal Blockset.

Shifts quantization steps by specific value, specified as a positive real scalar in %FS, FS, or LSB.

Note

The full scale range of the converter is defined as the difference between the last and first code on the +0.5 LSB compensated transfer curve. In a +0.5 LSB compensated transfer curve, first code is 0.5 LSB wide while the last code is 1.5 LSB wide. The input values must be considered within the full scale range of the converter.

Note

LSB is calculated by the equation LSB = Full scale range of converter2NBits.

Dependencies

To enable this parameter, set Measurement option to DC.

Programmatic Use

Block parameter: TargetOffsetError
Type: character vector
Values: real scalar
Default: 1.5 LSB

Data Types: double

Error on the slope of the straight line interpolating ADC transfer curve, specified as a positive real scalar in least significant bit %FS, FS, or LSB.

Note

The full scale range of the converter is defined as the difference between the last and first code on the +0.5 LSB compensated transfer curve. In a +0.5 LSB compensated transfer curve, first code is 0.5 LSB wide while the last code is 1.5 LSB wide. The input values must be considered within the full scale range of the converter.

Note

LSB is calculated by the equation LSB = Full scale range of converter2NBits.

Dependencies

To enable this parameter, set Measurement option to DC.

Programmatic Use

Block parameter: TargetGainError
Type: character vector
Values: real scalar
Default: 1 LSB

Data Types: double

Version History

Introduced in R2019a

See Also

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