In information theory, sampling is the process of converting a continuous signal into a discrete signal.
Theoretical sampling
A theoretical/ideal sampler results from multiplying a continuous signal with a Dirac comb. The resulting signal is then a scaled Dirac comb. The discrete signal would then be the sequence of scale values
Realizable sampling
Realizable samplers are called analog to digital converters (A/D converter or ADC).
Distortion
Sampling distortion is introduced when the sampler is nonideal. Various types of distortion can occur, such as:

Jitter: deviation from preciselyaccurate sample timing intervals

Integration effect: when a sampler has a nonzero width in which the sample is measured.

Noise: thermal sensor noise, analog circuit noise, etc.

Quantization error: roundoff error introduced by representing each sample as an integer at the output of an A/D converter

Slew rate limit error: error caused by an inability for an a/d converter output value to change sufficiently rapidly

Clipping: caused when the input signal exceeds the range of values that an a/d converter can represent at its output
The integration effect is readily noticeable in photography when the exposure is too long and creates a blur in the image. An ideal camera would have an exposure time of zero. In a capacitorbased sample and hold circuit, the integration effect is introduced because the capacitor cannot instantly change voltage thus requiring the sample to have nonzero width. Integration effects can be analyzed as a form of lowpass filtering.
Some of the other effects can often be analyzed by modeling them as random noise added to the sample values.
List of sampling topics
Sampling theory:
Definitions:
Sampling rates:
People:
Last updated: 05102005 04:19:48