DAC
A DAC converts digital codes into an analog signal, often a voltage or current. Different architectures suit different tasks, from setting a control level to generating a changing waveform.
The converter maps each input code to an analog output according to its transfer characteristic and reference. Updating the codes over time creates a waveform. Real outputs have finite settling time, noise and distortion, and sampled waveforms can require filtering.
In plain terms
A digitally controlled staircase of signal levels. More steps can make the staircase finer, but they do not guarantee every step is perfectly placed.
Why designers use it
- Generating analog control signals from digital commands.
- Producing waveforms for signal generation and communications.
- Converting digital audio into an analog signal with a suitable converter and output circuit.
Best for
- Analog setpoints
- Waveform generation
- Digital-to-analog signal paths
Key specifications
- Resolution and accuracy: Separate code count from actual output error
- Output and reference: Check range, loading, noise and reference requirements
- Dynamic performance: Check update rate, settling and spectral performance
When not to use it
- When the chosen DAC cannot meet the required output range, load, speed or error budget.
- When its interface or reference requirements do not match the system.
Common mistakes
- Treating resolution as guaranteed accuracy.
- Ignoring output settling, load and reference quality.
- Assuming a rapidly updated output is free of sampling images or needs no filtering.
Where you will find it
- TI's high-speed DAC guide shows digital samples becoming an analog waveform and explains the spectral images associated with sampling.
- A digital controller can request an analog level, provided the DAC and output circuit meet the load requirements.
A short history
DACs span multiple architectures and applications. TI's tutorial distinguishes sigma-delta, interpolating and high-speed converters, then explains sampling, spectral performance and digital processing. Those distinctions are more useful for choosing a converter than treating DACs as ordinary logic gates.
Good to know
- More digital codes do not automatically mean a more accurate analog output.
- Changing the update clock and changing the waveform frequency are different operations.