How Analog-to-Digital Conversion(ADC) Works

　・In Japanese
Prerequisite knowledge
　・Comparator
　・Binary number

When inputting analog voltage values ​​into a microcontroller or similar device for processing, they must be converted into digital values ​​(signals of 0 and 1, which are binary numbers). The method is as follows. There are several types of AD conversion(ADC) methods, but most of them basically use a comparator.

■Parallel ADC

The circuit diagram is as follows. The values ​​are tentative. The comparator compares all possible voltage values ​​with the input voltage, and identifies and converts the corresponding voltage value. This allows for high-speed conversion because the voltage values ​​are compared all at once, but since a comparator is required for each LSB, it is not good at converting to voltage values ​​with a large resolution.

■Successive Approximation Register ADC

The circuit diagram is as follows. Its features are that the processing speed is slower than the parallel type due to the repeated calculations, but it requires fewer comparators and enables highly accurate conversion.



To understand how it works, consider the case where an input voltage of 13V is converted into digital form. 13 can be expressed in binary as 4 bits as shown below, and is the sum of powers of 2 for each bit value.



Using this idea, the value of each bit is changed as shown below, and the reference voltage is compared with the input value to determine the input voltage (13V in this case).



From then on, change the bit value and perform the calculations as above.

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