ADC Testbench

Measures DC and AC performance metrics of ADC output

• Library:

• 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 radio (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

from adc digital — Digital signal from ADC output

scalar

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

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

from adc ready — Conversion ready signal from ADC output

scalar

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

to adc analog — Analog stimulus signal for ADC input

scalar

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

Data Types: double

to adc start — External start conversion clock for ADC

scalar

External start conversion clock for ADC, returned as a scalar. This signal starts the conversion process in ADC block.

Data Types: double

Parameters

Measurement — Select whether to measure DC or AC performance metrics

DC (default) | AC

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.

Recommended min. simulation stop time (s) — Minimum time simulation must run for meaningful result

2.048e-02 (default) | positive real scalar

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 20 times, assuming a ramp input that traverses the full scale range of the ADC over the period of simulation. Based on this assumption, the analog input frequency (f_analog), generated by the ADC Testbench block for the sawtooth waveform is set as:

  $$f_{\text{analog}}=\frac{StartFreq}{2^{(Nbits+1)}·10}$$

  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: $$T=\frac{1}{f_{\text{analog}}}$$.

• 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 [1] is given by:

  $$t=\frac{1.5·SamplingFrequency}{RBW}$$

  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

Set as model stop time — Automatically set recommended min. simulation stop time as model stop time

button

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

Endpoint — Measure DNL, INL using endpoint method

on (default) | off

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.

Best fit — Measure DNL, INL using best fit method

on (default) | off

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.

Plot DC analysis result — Plot DC analysis results

button

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.

Export measurement result — Store detailed test results to base workspace

button

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

Stimulus

Distortion measurement type — Type of distortion to measure

Harmonic (default) | Intermodulation

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

Dependencies

To enable this parameter, set Measurement option as AC.

Programmatic Use

Block parameter: DistortionMeasurement

Type: character vector

Values: Harmonic | Intermodulation

Default: Harmonic

Analog stimulus frequency (Hz) — Frequency of the analog input signal to ADC

positive real scalar | positive real valued vector

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.

• When the ADC Testbench is set to measure the Harmonic distortion, the default value of Analog stimulus frequency is 976.563.

• When the ADC Testbench is set to measure the Intermodulation distortion, the default value of Analog stimulus frequency is [878.907,1074.22].

Analog stimulus frequency needs to satisfy two requirements:

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

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

To satisfy both the conditions, use the equation $$f_{\text{analog}}=\frac{J}{M}{f}_{\text{start}}$$ [2],

where:

f_analog is the analog signal frequency,

f_start is the start conversion frequency,

$$M>2^{Nbits}·\pi$$, where Nbits is the number of bits of the ADC,

and J is an integer with no common factors with M.

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: 976.563

Resolution bandwidth (Hz) — Resolution bandwidth

positive real scalar

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.

• When the ADC AC Measurement is set to measure the Harmonic distortion, the default value of Resolution bandwidth (Hz) is 97.6563.

• When the ADC AC Measurement is set to measure the Intermodulation distortion, the default value of Resolution bandwidth (Hz) is 87.8907.

Dependencies

To enable this parameter, set Measurement option as AC.

Programmatic Use

Block parameter: RBW

Type: character vector

Values: positive real scalar

Default: 97.6563

Start conversion frequency (Hz) — Frequency of the start conversion clock of the ADC

1e6 (default) | positive real scalar

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 (s) — RMS aperture jitter to be added by the start conversion clock

40e-12 (default) | positive real scalar

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

Error tolerance (LSB) — Maximum difference between successive samples of analog signal

0.1 (default) | positive scalar in the range (0, 1]

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

Setup

Autofill setup parameter — Automatically propagate setup parameters from ADC

button

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 bits — Number of physical output bits

10 (default) | positive real integer in the range [1, 26]

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

Input range (V) — ADC dynamic range

[-1 1] (default) | 2-element row vector

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

Programmatic Use

• Use get_param(gcb,'InputRange') to view the current Input range (V).

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

Data Types: double

Hold off time (s) — Delay before measurement analysis

0 (default) | nonnegative real scalar

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

Show spectrum analyzer during simulation — Displays spectrum analyzer during simulation

off (default) | on

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

Dependencies

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

Enable increased buffer size — Enable increased buffer size

off (default) | on

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

Buffer size — Number of samples of the input buffering available during simulation

5 (default) | positive integer scalar

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

Autofill target metric — Automatically propagate target metrics from ADC

button

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.

Offset error — Shifts quantization steps by specific value

1.5 LSB (default) | real scalar

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

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

Gain error — Error on the slope of ADC transfer curve

1 LSB (default) | real scalar

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.

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

References

[1] Spectrum Analyzer

[2] IEEE Std 1241-2010. "IEEE Standard for Terminology and Test Methods for Analog-to-Digital Converters," pp. 29-30, 14 January 2011.