A/D conversion method for serial/parallel A/D converter, and serial/parallel A/D converter

摘要

The present invention provides a serial/parallel A/D converter which is capable of performing a high-speed and high-accuracy operation even in the case where an analog input voltage Vin greatly varies in a period between a previous sampling period in which the analog input voltage is held and the next sampling period, when converting the analog input voltage Vin input into a digital value. This serial/parallel A/D converter includes a lower-order reference voltage initializing circuit 8 for initializing a lower-order reference voltage to an initialization voltage Vrc 23. The initialization voltage Vrc 23 is generated as the lower-order reference voltage in an arbitrary period from the start of sampling of the analog input voltage until the start of a comparison operation for the lower-order reference voltage, the value of the lower-order reference voltage is changed from the value of the initialization voltage to a voltage value which is decided on the basis of higher-order code selection signals P0C-P3C from a higher-order code selecting circuit 14, and the value of the lower-order reference voltage which is decided on the basis of the higher-order code selection signals P0C-P3C is compared with the value of the analog input voltage.