A/D conversion device

1. An A/D conversion device capable of switching between a comparator function and an A/D conversion function, comprising:

a sample-and-hold circuit that holds a received input analog voltage;

a sequential conversion register that stores a digital value corresponding to a threshold for comparison and determination in the comparator function;

a D/A converter that generates an analog voltage corresponding to the digital value stored in the sequential conversion register;

a comparator that compares an analog voltage output from the sample-and-hold circuit with an analog voltage obtained from the D/A converter, and outputs a comparison result;

a comparison result counter that outputs a determination result according to a count number counted based on the comparison result; and

a control circuit that performs control for switching from the comparator function to the A/D conversion function, based on the determination result,

wherein, during operation of the A/D conversion function, the sequential conversion register performs an A/D conversion processing for sequentially converting the analog voltage held in the sample-and-hold circuit into a digital value.

2. The A/D conversion device according to claim 1 , wherein, during operation of the comparator function, the comparator compares an analog voltage output from the sample-and-hold circuit with an analog voltage corresponding to the threshold and obtained from the D/A converter, and outputs the comparison result.

3. The A/D conversion device according to claim 1 , wherein the control circuit comprises:

a comparator control circuit that allows the comparator function to be continuously operated; and

an A/D conversion control circuit that starts operation of the A/D conversion function according to the comparison result obtained during operation of the comparator function.

4. The A/D conversion device according to claim 1 , wherein

the sample-and-hold circuit performs a sampling processing on the input analog voltage during operation of the comparator function, and

the sample-and-hold circuit performs no sampling processing on the input analog voltage during operation of the A/D conversion function.

5. The A/D conversion device according to claim 1 , wherein the comparison result counter performs counting when the comparison result output from the comparator matches a previous comparison result, and clears the count value to 0 when the comparison result output from the comparator does not match the previous comparison result.

6. The A/D conversion device according to claim 1 , wherein when the count value is equal to or greater than a preset count value, the comparison result counter outputs the determination result indicating that a count condition is satisfied.

7. The A/D conversion device according to claim 1 , wherein the control circuit allows operation of the comparator function to be re-executed, after the A/D conversion processing is completed by the sequential conversion register.

8. The A/D conversion device according to claim 1 , further comprising a conversion result register that holds a digital value obtained after A/D conversion and received from the sequential conversion register, and outputs the digital value as an A/D conversion result.

9. The A/D conversion device according to claim 1 , wherein

the sequential conversion register alternately stores digital values corresponding to a first threshold and a second threshold, and

the comparison result counter outputs the determination result according to a count value counted based on both the comparison result corresponding to the first threshold and the comparison result corresponding to the second threshold, the comparison results being output from the comparator.

10. The A/D conversion device according to claim 9 , wherein when the analog voltage output from the sample-and-hold circuit falls within a voltage range between the first threshold and the second threshold, the comparison result counter performs counting.