# DAC AC Measurement

Measure AC performance metrics of DAC output

**Library:**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

## Ports

### Input

`digital`

— Digital input signal from DAC

scalar

Digital input 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

`Digital signal frequency (Hz)`

— Frequency of digital input signal to DAC

`1e3`

(default) | positive real scalar

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`

`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`

`Settling time tolerance (LSB)`

— Tolerance for calculating settling time

`0.5`

(default) | positive real scalar

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`

`Hold off time (s)`

— Delay before measurement analysis to avoid corruption by transients

`0`

(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:
`0` |

`Recommended simulation stop time (s)`

— Minimum time simulation must run for meaningful result

`0.09`

(default) | positive real scalar

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]:

$$T=6\left(\frac{1.5}{RBW}+\text{Holdofftime}\right)$$,

where *RBW* is the resolution bandwidth of the spectrum estimator
inside the DAC Testbench block and is given by the equation: $$RBW=\left[\mathrm{min}\left(\text{Inputfrequency}\right)0.1\right]$$.

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

**Data Types: **`double`

`Output result to base workspace`

— Store detailed test results to base workspace

off (default) | on

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_ac_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_ac_out` |

`Show spectrum analyzer during simulation`

— Displays Spectrum Analyzer during simulation

on (default) | off

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

## More About

### SNR

Signal-to-noise ratio or SNR is the ratio of the RMS (root-mean-square) signal amplitude to the mean value of the root-sum-squares (RSS) of all other spectral components, excluding the DC and first five harmonics.

### SINAD

Signal to noise and distortion ratio or SINAD is the ratio of the RMS signal amplitude to the mean value of the root-sum-squares of all other spectral components and harmonics, excluding DC.

### SFDR

Spurious free dynamic range or SFDR is the ratio of the RMS signal amplitude to the RMS value of the peak spurious content, measured over the entire first Nyquist zone (DC to half of sampling frequency).

### ENOB

Effective number of bits or ENOB represents the actual resolution of a DAC after considering internal noise and errors. It is given by $$\text{ENOB}=\frac{\text{SINAD}-1.76}{6.02}$$.

## See Also

**Introduced in R2020a**

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