An Analog to Digital converter (ADC) takes samples of an analog signal and uses the samples to produce a digital signal. The samples are quantized so that at each sampling time only one of 2K numbers is generated by a K-bit ADC. The most common ADCs sample analog voltages and generate numbers, typically in binary form, representing the voltage.
The signal amplitude levels, or thresholds, that the ADC uses to generate the digital numbers are usually taken to be equally-spaced in amplitude for a general purpose ADC. In some ADCs, however, the thresholds are non-linearly spaced, such as converters conforming to the well-known μ-law or A-law conversion format used in many voiceband communication systems. These systems implement an approximate logarithmic transfer function using piecewise linear segments, each segment having a different slope so that the regions around the lower amplitude levels suffer less quanitzation error. In this way, these ADCs, using only eight data bits, are able to provide an acceptable signal-to-noise ratio for the low amplitude signals while maintaining a relatively wide dynamic range, whereas twelve bits would be required in a linear ADC to achieve the similar dynamic range and signal to noise ratio.