Binary Weighted DAC

N-bit DAC based on R-2R weighted resistor architecture

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• Mixed-Signal Blockset / DAC / Architectures

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Description

The R-2R DAC is one of the most common types of Binary-Weighted DACs. It consists of a parallel binary-weighted resistor bank. Each digital level is converted to an equivalent analog signal by the resistor bank.

The input/output transfer curve of the binary weighted DAC can be nonmonotonic, which means that the transfer curve can reverse its direction.

The R-2R DAC architecture is low resolution and consumes more power due to the large number of resistors required to implement the architecture.

Ports

Input

digital — Digital input signal to DAC

scalar

Digital input signal to DAC, specified as a scalar.

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

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.

Dependencies

To enable this port, select Use external start clock in the General tab.

Data Types: double

Output

analog — Converted analog output signal

scalar

Converted analog output signal, returned as a scalar.

Data Types: double

ready — Determines whether digital-to-analog conversion is complete

scalar

Determines whether the digital-to-analog conversion is complete, returned as a scalar.

Dependencies

To enable this port, select Show ready port in the General tab.

Data Types: double

Parameters

General

Number of bits — Number of bits in input word

5 (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: 5

Data Types: double

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

Use external start clock — Connect to external start conversion clock

on (default) | off

Select to connect to an external start conversion clock. By default, this option is selected. If you deselect this option, a Sampling Clock Source block inside the Segmented DAC is used to generate the start conversion clock

Conversion start 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 Conversion start frequency parameter determines the conversion rate at the start of conversion.

Dependencies

To enable this parameter, deselect Use external start clock.

Programmatic Use

Block parameter: StartFreq

Type: character vector

Values: positive real scalar

Default: 1e6

Data Types: double

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:

$$\text{DAC output = }\left(\left(\frac{\text{Digital input code}}{2^{\text{Number of bits}}}\right)\text{Reference}\right)+\text{Bias}$$.

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:

$$\text{DAC output = }\left(\left(\frac{\text{Digital input code}}{2^{\text{Number of bits}}}\right)\text{Reference}\right)+\text{Bias}$$.

Programmatic Use

Block parameter: Bias

Type: character vector

Values: real scalar

Default: 0

Data Types: double

Show ready port — Enable ready port on block

off (default) | on

Select to enable the ready port on the block. This option is deselected by default.

Impairments

Enable impairments — Enable impairments in DAC simulation

on (default) | off

Select to enable impairments such as offset error and gain error in DAC simulation. This parameter is selected. by default.

Offset error — Shifts quantization steps by specific value

0 LSB (default) | real scalar

Shifts quantization steps by a specific value, specified as a scalar in %FS (percentage full scale), FS (full scale), or LSB (least significant bit).

Offset error is applied before Reference (V) and Bias (V).

Dependencies

To enable this parameter, select Enable impairments in the Impairments tab.

Programmatic Use

Block parameter: OffsetError

Type: character vector

Values: real scalar

Default: 0 LSB

Data Types: double

Gain error — Error in slope of DAC transfer curve

0 LSB (default) | real scalar

Error in the slope of the straight line interpolating the DAC transfer curve, specified as a real scalar in %FS (percentage full scale), FS (full scale), or LSB (least significant bit).

Gain error is applied before Reference (V) and Bias (V).

Dependencies

To enable this parameter, select Enable impairments in the Impairments tab.

Programmatic Use

Block parameter: GainError

Type: character vector

Values: real scalar

Default: 0 LSB

Data Types: double

Settling time (s) — Time required for output to settle

2e-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: 2e-7

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

Model Examples

Measure Offset and Gain Error of Binary Weighted DAC

Find the offset and gain errors of a binary weighted DAC block.

Measure AC Performance Metrics of Binary Weighted DAC

Find the AC performance metrics such as SNR, SINAD, SFDR, ENOB, noise floor and settling time of a binary weighted DAC block.