# DAC DC Measurement

Measure DC performance metrics of DAC output

**Library:**Mixed-Signal Blockset / DAC / Measurements & Testbenches

## Description

The DAC DC Measurement block measures DAC DC performance metrics such as offset error, gain error, integral nonlinearity (INL), and differential nonlinearity (DNL) errors. You can use the DAC DC Measurement block to validate the DAC architecture models provided in Mixed-Signal Blockset™, or you can use a DAC of your own implementation.

## Ports

### Input

`digital`

— Digital input signal from DAC

scalar

Digital signal from a DAC, specified as a scalar.

**Data Types: **`fixed point`

| `single`

| `double`

| `int8`

| `int16`

| `int32`

| `uint8`

| `uint16`

| `uint32`

`analog`

— Converted analog signal from DAC

scalar

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

**Data Types: **`double`

`start`

— External clock to start conversion

scalar

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

**Data Types: **`double`

## Parameters

`Input polarity`

— Polarity of input signal to DAC

`Bipolar`

(default) | `Unipolar`

Polarity of the input signal to the DAC.

#### Programmatic Use

Block parameter:
`Polarity` |

Type: character vector |

Values:
`Bipolar` |`Unipolar` |

Default:
`Bipolar` |

`Reference (V)`

— Reference voltage

`2`

(default) | real scalar

Reference voltage of the DAC, specified as a real scalar in volts. **Reference
(V)** helps determine the output from the input digital code,
**Number of bits**, and **Bias (V)** using the
equation:

$$\text{DACoutput=}\left(\left(\frac{\text{Digitalinputcode}}{{2}^{\text{Numberofbits}}}\right)\text{Reference}\right)+\text{Bias}$$.

#### Programmatic Use

Block parameter:
`Ref` |

Type: character vector |

Values: real scalar |

Default:
`2` |

**Data Types: **`double`

`Bias (V)`

— Bias voltage added to output

`0`

(default) | real scalar

Bias voltage added to the output of the DAC, specified as a real scalar in volts.
**Bias (V)** helps determine the output from the input digital
code, **Number of bits**, and **Reference (V)** using
the equation:

$$\text{DACoutput=}\left(\left(\frac{\text{Digitalinputcode}}{{2}^{\text{Numberofbits}}}\right)\text{Reference}\right)+\text{Bias}$$.

#### Programmatic Use

Block parameter:
`Bias` |

Type: character vector |

Values: real scalar |

Default:
`0` |

**Data Types: **`double`

`Settling time (s)`

— Time required for output to settle

`3e-7`

(default) | nonnegative real scalar

The time required for the output of the DAC to settle to within some fraction of its final value, specified as a nonnegative real scalar in seconds.

#### Programmatic Use

Block parameter:
`SettlingTime` |

Type: character vector |

Values: real scalar |

Default:
`3e-7` |

**Data Types: **`double`

`Hold off time (s)`

— Delay before measurement analysis

`1e-3`

(default) | nonnegative real scalar

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:
`1e-3` |

**Data Types: **`double`

`Number of bits`

— Number of bits in input word

`10`

(default) | positive real integer

Number of bits in the input word, specified as a unitless positive real integer.
**Number of bits** determines the resolution of the DAC.

#### Programmatic Use

Block parameter:
`NBits` |

Type: character vector |

Values: positive real integer |

Default:
`10` |

**Data Types: **`double`

`Start conversion frequency (Hz)`

— Frequency of internal start conversion clock

`1e6`

(default) | positive real scalar

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`

`Recommended simulation stop time (s)`

— Minimum time simulation must run for meaningful result

`0.02148`

(default) | positive real scalar

Minimum time 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 the DAC can sample each
digital code 20 times. Based on this assumption, the **Recommended simulation
stop time (s)**
*T* is given by:

$$T=\frac{\text{Samplesperbit}}{\left(StartFreq/{2}^{Nbits+1}\right)}+\text{Holdofftime}$$,

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

The number of samples per bit is calculated using the equation:

$$\text{Samplesperbit=}\mathrm{max}\left(\frac{1}{\text{Errortolerance}},10\right)$$.

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

**Data Types: **`double`

`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 endpoints of the actual transfer function to measure the DNL and INL errors.

`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 errors.

`Output result to base workspace`

— Store detailed test results to base workspace

off (default) | on

Select to 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.

`Workspace variable name`

— Name of the variable that stores detailed test results

`dac_dc_out`

(default) | character string

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_dc_out` |

`Plot`

— Plot measurement results

button

Click to plot measurement result for further analysis.

## More About

### Offset Error

Offset error represents the offset of the DAC transfer function curve from it ideal value at a single point.

### Gain Error

Gain error represents the deviation of the slope of the DAC transfer function curve from its ideal value.

### INL Error

Integral nonlinearity (INL) error, also termed as relative accuracy, is the maximum deviation of the measured transfer function from a straight line. The straight line can either be a best fit using standard-curve fitting technique, or be drawn between the endpoints of the actual transfer function after gain adjustment.

The best fit method gives a better prediction of distortion in AC applications, and a lower value of linearity error. The endpoint method is mostly used in the measurement applications of data converters, since the error budget depends on actual deviation from the ideal transfer function.

### DNL Error

Differential nonlinearity (DNL) is the deviation from the ideal difference (1 LSB) between analog input levels that trigger any two successive digital output levels. The DNL error is the maximum value of DNL found at any transition.

## See Also

**Introduced in R2020a**

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