US 2003/0222806 A1Published application

AD converter circuit and AD conversion method

AssigneeFujitsu Limited

InventorsShogo Ito, Hisao Suzuki

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Abstract

This invention provides an AD converter circuit and an AD conversion method capable of executing AD conversion up to the lowest bit properly even under a high-speed operation. The AD converter circuit 1 comprises high-order-comparators D1-D3, low-order comparator D0 and a comparison reference voltage source 10 having seven reference voltage output points V1-V3, Va-Vd. The reference voltage output points V1-V3 are connected to the reference voltage terminals of the high-order-comparators D1-D3. The reference voltage output points Va-Vd are connected to a point A having parasitic capacitance through analog switches SWA-SWD. The point A is connected to the reference voltage terminal of the low-order comparator D0 through an analog switch SW2 and an input voltage VIN through an analog switch SWE.

Claims11

Dependent claims

An AD converter circuit comprising:

an input voltage terminal;
a comparison reference voltage source having plural reference voltage output points;
a high-order-bit comparator for determining digital value of high-order-bit by comparing voltage at reference voltage output points spaced at an interval of the comparison reference voltage source with voltage of the input voltage terminal;
a low-order comparator for determining digital value of low-order bit by comparing the voltage of remaining reference voltage output points of the comparison reference voltage source with voltage of the input voltage terminal;
a reference voltage input line for inputting reference voltage into reference voltage terminal of the low-order-bit comparator;
a first-switch-element group for switching opening/closing between reference voltage output points of the comparison reference voltage source other than the one connected to the high-order-bit comparator and the reference voltage input line;
and
a second switch element for switching opening/closing between the input voltage terminal and the reference voltage input line.

5 more elements

An AD conversion method of an AD converter circuit comprising:

a comparison reference voltage source having plural reference voltage output points;
a high-order-bit comparator for determining digital value of high-order-bit by comparing voltage at reference voltage output points spaced at an interval of the comparison reference voltage source with input voltage;
a low-order comparator for determining the digital value of low-order bit by comparing voltage of remaining reference voltage output points of the comparison reference voltage source with input voltage;
and a reference voltage input line for inputting reference voltage into reference voltage terminal of the low-order-bit comparator, the AD conversion method comprising:
separating the reference voltage input line from all the reference voltage output points of the comparison reference voltage source and fetching input voltage into the reference voltage input line;
separating the reference voltage input line from input voltage and making the high-order-bit comparator to determine the high-order-bit;
connecting the reference voltage input line to a reference voltage output point of the comparison reference voltage source other than the reference voltage output points connected to the high-order-bit comparator and corresponding to the result of determination of the high-order-bit;
and
making the low-order-bit comparator to determine the low-order bit.

6 more elements

Dependencies are inferred from the claim text.