A/D (Analogue-to-Digital) converter is a "mixed signal" circuit which performs digitization of the external analogue signals. In the dsPIC30F family there are two microcontroller versions one with 10-bit and the other with 12-bit A/D converter. It has been shown in practice that for the control or regulation systems the 10-bit A/D converters gave satisfactory solutions. The additional bits in the A/D converters in these applications are almost unsuable because they are masked by the high levels of electro-magnetic noise. In the measuring systems the practice showed that with the 12-bit converters one could achieve a good compromise between the sampling rate and accuracy (0.02% for a 12-bit converter).
The 10-bit A/D converter microcontrollers could sample up to 16 analogue inputs with the frequency of 500kHz applying the successive approximation (SAR) conversion. The successive approximation conversion method is one of the basic types of A/D conversion. It is carried out in several steps until the input voltage is equal to the internally generated voltage. The speed of conversion of this type of A/D converters is limited, but they are sufficiently fast for most of the general purpose applications. This 10-bit A/D converter has the ability of using external voltage references, simultaneous sampling of up to four analogue inputs in the Sample/Hold amplifiers (sampling of several signals at one time is possible), automatic channel scan mode, and selectable conversion trigger source. The conversion result is loaded to a 16-word buffer register in four selectable output formats (two integer and two floating point). In addition, the A/D converter could operate in SLEEP or IDLE mode.
The performance of microcontrollers having 12-bit A/D converter is somewhat inferior to this, but their conversion accuracy is higher. They could sample up to 16 analogue inputs with 100kHz frequency applying the successive approximation conversion. The converter can use the external voltage references, sample only one of the 16 analogue inputs in the Sample/Hold amplifier, it has automatic channel scan mode and selectable conversion trigger source. Like the 10-bit converter, the conversion result is loaded to a 16-word buffer register in four selectable output formats (two integer and two floating point). In addition, the A/D converter could operate in SLEEP or IDLE mode.