By Len Staller
Embedded Systems Design
(02/24/05, 05:24:00 PM EST)
Embedded Systems Design
(02/24/05, 05:24:00 PM EST)
DC accuracy
Many signals remain relatively static, such as those from temperature sensors or pressure transducers. In such applications, the measured voltage is related to some physical measurement, and the absolute accuracy of the voltage measurement is important. The ADC specifications that describe this type of accuracy are offset error, full-scale error, differential nonlinearity (DNL), and integral nonlinearity (INL). These four specifications build a complete description of an ADC's absolute accuracy.
Although not a specification, one of the fundamental errors in ADC measurement is a result of the data-conversion process itself: quantization error. This error cannot be avoided in ADC measurements. DC accuracy, and resulting absolute error are determined by four specs—offset, full-scale/gain error, INL, and DNL. Quantization error is an artifact of representing an analog signal with a digital number (in other words, an artifact of analog-to-digital conversion). Maximum quantization error is determined by the resolution of the measurement (resolution of the ADC, or measurement if signal is oversampled). Further, quantization error will appear as noise, referred to as quantization noise in the dynamic analysis. For example, quantization error will appear as the noise floor in an FFT plot of a measured signal input to an ADC, which I'll discuss later in the dynamic performance section).
Reference:
- http://www.embended.com/
- http://en.wikipedia.org
