Sensor Circuits - The Electronic Nose Artificial Olfaction Technology - page 191

Fig. 7.19 Response of filter a-d Frequency

Digital to Analog Converter (DAC) and Analog to Digital Converter (ADC) work
as the interface between digital/analog devices. They are also defined as mixed-
signal devices as they perform both analog and digital functions.
There are many methods available to convert the analog signal in to digital
signal. They are counter, single slope ADC, dual slope ADC, Flash, delta and
sigma, and successive approximation ADC. In particular, ADC is an electronic
integrated circuit which transforms a signal from analog (continuous) to digital
(discrete) form. As digital forms of signals are less susceptible to the deleterious
effects of additive noise, ADC is required.
ADC provides a link between the analog transducers, the digital signal pro-
cessing, and data handling. Almost everywhere ADC is used where an analog
signal has to be processed, stored, or transported in digital form. Some examples of
ADC applications are digital volt meters, cell phone, thermocouples, and digital
oscilloscope. Comparison of different types of ADCs is shown in Table 7.1 and the
basic process of ADC is illustrated in Fig. 7.20 .
Quantizing: In binary partitioning the reference signal ranges to a number of
discrete quanta, then matching the input signal to the correct quantum.

Table 7.1 ADC Types: comparison

Type Speed (Relative) Cost (Relative)

Dual slope Slow Medium

Flash Very fast High

Successive approximately Medium-fast Low

Sigma-delta Slow low