What Is an ADC (Analog-to-Digital Converter)?
An ADC (Analog-to-Digital Converter) is a circuit that converts a continuously changing analog voltage into digital values the processor can understand. For the general concept see the what are ADC and DAC article.
How Does It Work?
An ADC samples the signal at regular intervals and rounds each sample to the nearest digital level (quantization). The output is a binary number representing the input's magnitude at that moment.
Resolution
The number of bits sets the resolution: an 8-bit ADC distinguishes 256 levels, a 12-bit one 4096 levels. Higher resolution means finer measurement; sampling rate and resolution are considered together.
| Type | Property |
|---|---|
| SAR | Fast, medium resolution (general purpose) |
| Sigma-Delta | Very high resolution, slow |
| Flash | Very fast, low resolution |
Relationship to the DAC
An ADC converts from analog to digital; a DAC does the opposite. Together they bridge digital systems and the real world.
Where Is It Used?
Sensor reading (temperature, pressure), audio recording, microcontroller input stages, measurement instruments and data-acquisition systems.
Single-Ended and Differential Input
ADC inputs come in two forms: single-ended measures the signal relative to ground, while differential measures the difference between two inputs. Because a differential input suppresses common-mode noise, it's preferred for precise measurements in long-cable or noisy environments.
Common Mistakes
- Reference voltage: an unstable reference shifts the whole measurement.
- Aliasing: if the sampling rate is too low, false frequencies appear; an anti-alias filter is needed.
- Input impedance: if the source is very high-impedance, sampling is faulty; a buffer is needed.
Frequently Asked Questions
How many bits of ADC are needed?+
What is a SAR ADC?+
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