Pipeline A/D converter

1. A pipeline A/D converter comprising:

a control section for outputting a control signal according to the operation state of an apparatus incorporating said pipeline A/D converter; and

a pipeline A/D conversion section, the resolution and/or allowable conversion processing rate of which are switched by switching the capacitance in a built-in operational amplifier according to said control signal, the operational amplifier comprising:

an operational amplifier circuit;

a first switch-capacitance device group which is set to have capacitance values suited for high resolution; and

a second switch-capacitance device group which is set to have capacitance values suited for low resolution.

2. A pipeline A/D converter in accordance with claim 1 , wherein said control section further switches the conductance of the output stage of a differential amplifier circuit incorporated in said operational amplifier according to the capacitance in said operational amplifier, said capacitance having been switched according to said control signal.

3. The pipeline A/D converter of claim 1 , wherein the pipeline A/D converter further comprises:

plural pipe stages, each pipe stage having the operational amplifier, each operational amplifier having the same configuration;

a first operational amplifier having means for sampling and holding analog input signals, the first operational amplifier having the same configuration as the operational amplifiers of the plural pipe stages; and

a digital demodulator circuit that performs an arithmetic operation based on digital output signals from the plural pipe stages, and that outputs an N-bit digital signal,

each of the plural pipe stages being connected in turn as a subsequent stage of the first operational amplifier, and

the pipeline A/D conversion switching the capacitance in the operational amplifier section by selecting either the first switch-capacitance device group or the second switch-capacitance device group according to said control signal.

4. A pipeline A/D converter comprising:

a control section that outputs a test signal, receives a digital signal output from a pipeline A/D conversion section to which said test signal has been input, tests whether said digital signal is proper or not, and outputs a control signal according to the result of the test; and

an operational amplifier including:

an operational amplifier circuit;

a first switch-capacitance device group which is set to have capacitance values suited for high resolution; and

a second switch-capacitance device group which is set to have capacitance values suited for low resolution,

the resolution of the pipeline A/D conversion section being switched by switching the capacitance in the operational amplifier according to the control signal.

5. A pipeline A/D converter in accordance with claim 4 , wherein said control section outputs said test signal at the time when an apparatus incorporating said pipeline A/D converter is in a predetermined state.

6. The pipeline A/D converter of claim 4 , wherein the pipeline A/D converter further comprises:

plural pipe stages, each pipe stage having the operational amplifier, each operational amplifier having the same configuration;

a first operational amplifier having means for sampling and holding analog input signals, the first operational amplifier having the same configuration as the operational amplifiers of the plural pipe stages; and

a digital demodulator circuit that performs an arithmetic operation based on digital output signals from the plural pipe stages, and that outputs an N-bit digital signal,

each of the plural pipe stages being connected in turn as a subsequent stage of the first operational amplifier, and

the pipeline A/D conversion switching the capacitance in the operational amplifier section by selecting either the first switch-capacitance device group or the second switch-capacitance device group according to said control signal.

7. A pipeline A/D converter comprising:

a control section that outputs a test signal, receives a digital signal output from a pipeline A/D conversion section to which said test signal has been input, tests whether said digital signal is proper or not, and outputs a control signal according to the result of the test; and

an operational amplifier including:

an operational amplifier circuit;

a first switch-capacitance device group which is set to have capacitance values suited for high resolution; and

a second switch-capacitance device group which is set to have capacitance values suited for low resolution,

the allowable conversion processing rate of the pipeline A/D conversion section being switched by switching the capacitance in the operational amplifier according to the control signal.

8. The pipeline A/D converter of claim 7 , wherein the pipeline A/D converter further comprises:

plural pipe stages, each pipe stage having the operational amplifier, each operational amplifier having the same configuration;

a first operational amplifier having means for sampling and holding analog input signals, the first operational amplifier having the same configuration as the operational amplifiers of the plural pipe stages; and

a digital demodulator circuit that performs an arithmetic operation based on digital output signals from the plural pipe stages, and that outputs an N-bit digital signal,

each of the plural pipe stages being connected in turn as a subsequent stage of the first operational amplifier, and

the pipeline A/D conversion switching the capacitance in the operational amplifier section by selecting either the first switch-capacitance device group or the second switch-capacitance device group according to said control signal.