Signal processing device and control method for signal processing device

A signal processing device comprising:

• a filter circuit including a first capacitor for reducing a predetermined frequency component of an analog signal;
• a sample-and-hold circuit including a second capacitor for sampling and holding the analog signal that has passed through the filter circuit;
• an AD conversion circuit for converting an output signal from the sample-and-hold circuit into a digital signal;
• a voltage application circuit for applying a predetermined voltage to the second capacitor;
• and
• a control unit for applying the predetermined voltage to the second capacitor through the voltage application circuit, thereby charging the second capacitor, and then causing the sample-and-hold circuit to sample the analog signal that has passed through the filter circuit, wherein
• the sample-and-hold circuit includes a first switch for switching between a sample mode and a hold mode, and
• the voltage application circuit includes a second switch connected in parallel with the first switch, the second switch controlling electrical connection between a power supply whose output voltage is the predetermined voltage, and the second capacitor, and
• the signal processing device further comprising a third switch on a line that connects the ground and a point between the first switch and the sample-and-hold circuit.

A signal processing device comprising:

• a filter circuit including a first capacitor for reducing a predetermined frequency component of an analog signal;
• a sample-and-hold circuit including a second capacitor for sampling and holding the analog signal that has passed through the filter circuit;
• an AD conversion circuit for converting an output signal from the sample-and-hold circuit into a digital signal;
• a voltage application circuit for applying a predetermined voltage to the second capacitor;
• and
• a control unit for applying the predetermined voltage to the second capacitor through the voltage application circuit, thereby charging the second capacitor, and then causing the sample-and-hold circuit to sample the analog signal that has passed through the filter circuit, wherein
• the sample-and-hold circuit includes a first switch for switching between a sample mode and a hold mode,
• the voltage application circuit includes a second switch connected in parallel with the first switch, the second switch controlling electrical connection between a power supply whose output voltage is the predetermined voltage, and the second capacitor,
• the control unit
• switches the second switch to on from off to charge the second capacitor equivalent to the predetermined voltage,
• switches the second switch to off from on to cause a signal equivalent to the predetermined voltage to be output from the sample-and-hold circuit,
• switches the first switch to on from off to charge the second capacitor equivalent to the voltage of the analog signal, and
• switches the first switch to off from on to cause a signal equivalent to the voltage of the analog signal to be output from the sample-and-hold circuit.