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

Output

analog — Converted analog output signal

scalar

Converted analog output signal, returned as a scalar.

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

• 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 polarity — Polarity of input signal to DAC

Bipolar (default) | Unipolar

Polarity of the input signal to the DAC.

Programmatic Use

• Use get_param(gcb,'Polarity') to view the current Input polarity.

• Use set_param(gcb,'Polarity',value) to set Input polarity to a specific value.

Conversion start frequency (Hz) — Frequency of internal start-conversion clock

1e6 (default) | positive real scalar

Frequency of internal start-conversion clock, specified as a positive real scalar in Hz. Conversion start frequency (Hz) determines the rate of the DAC.

Programmatic Use

• Use get_param(gcb,'StartFreq') to view the current value of Conversion start frequency (Hz).

• Use set_param(gcb,'StartFreq',value) to set Conversion start frequency (Hz) to a specific value.

Data Types: double

RMS aperture jitter (s) — RMS aperture jitter added to start-conversion clock

1e-12 (default) | real nonnegative scalar

RMS aperture jitter added as an impairment to the start-conversion clock, specified as a real nonnegative scalar in seconds. Set RMS aperture jitter to zero if you want a clean signal from the clock.

Programmatic Use

• Use get_param(gcb,'StartClkJitter') to view the current value of RMS aperture jitter (s).

• Use set_param(gcb,'StartClkJitter',value) to set RMS aperture jitter (s) to a specific value.

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

• Use get_param(gcb,'Ref') to view the current value of Reference (V).

• Use set_param(gcb,'Ref',value) to set Reference (V) to a specific value.

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

• Use get_param(gcb,'Bias') to view the current value of Bias (V).

• Use set_param(gcb,'Bias',value) to set Bias (V) to a specific value.

Data Types: double

Impairments

Enable impairments — Enable impairments in DAC simulation

off (default) | on

Select to enable impairments such as offset error and gain error in DAC simulation. By default, this parameter is deselected.

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

• Use get_param(gcb,'OffsetError') to view the current value of Offset error.

• Use set_param(gcb,'OffsetError',value) to set Offset error to a specific value.

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

• Use get_param(gcb,'GainError') to view the current value of Gain error.

• Use set_param(gcb,'GainError',value) to set Gain error to a specific value.

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, and noise floor of a binary weighted DAC block.