What Is a DAC (Digital-to-Analog Converter)?
A DAC (Digital-to-Analog Converter) is a circuit that converts a digital (binary) value into a corresponding analog voltage. It does the opposite of an ADC; for the general concept see the what are ADC and DAC article.
How Does It Work?
It takes the binary number from the processor and produces an output voltage proportional to that number. As the number rises, the output voltage rises step by step; when successive samples combine, a continuous analog wave forms.
Resolution
The number of bits sets the fineness of the output steps: an 8-bit DAC produces 256 steps, a 12-bit one 4096 steps. Higher resolution means a smoother analog output.
| Type | Property |
|---|---|
| R-2R ladder | Simple, fast, common |
| Sigma-Delta | High resolution (audio) |
| String DAC | Monotonic, precise |
Why Is Filtering Needed?
A DAC's output is stepped; a low-pass filter is placed at the output for a smooth analog signal. This softens the steps and produces a clean wave.
Where Is It Used?
Audio generation (music players, before an audio amplifier), motor/actuator control, signal generators and voltage-setting circuits.
Built-in and External DAC
Some microcontrollers include a built-in DAC; this is enough for simple applications. When high resolution, low noise or high speed is needed, external DAC chips connected over I2C/SPI are used. In applications wanting quality analog output such as audio, an external, dedicated DAC is preferred.
Common Mistakes
- Skipping the filter: an unfiltered output is stepped and noisy.
- Load effect: a low-impedance load pulls the output down; a buffer/op-amp is needed.
- Reference: the output accuracy depends on the reference voltage.
Frequently Asked Questions
Is PWM a DAC?+
What is R-2R?+
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