Method for improving successive approximation analog-to-digital converter

A signal converting method for an analog-to-digital converter (ADC) that is used for converting an analog input signal into a digital output signal, the analog-to-digital converter comprising:

• a successive approximation register (SAR) for storing a digital bit stream of predetermined bit length;
• a digital-to-analog converter (DAC) comprising:
• a first voltage divider unit having an input end electrically connected to a first predetermined voltage, the first voltage divider unit comprising:
• a first resistor having a resistance approaching a first resistance value;
• and
• a first switch electrically connected to the first resistor for controlling if an output end of the first divider unit electrically connects to the input end;
• a second voltage divider unit having an input end electrically connected to the first predetermined voltage, the second voltage divider unit comprising:
• a second resistor having a resistance approaching the first resistance value;
• and
• a second switch electrically connected to the second resistor for controlling if an output end of the second divider unit electrically connects to the input end;
• a third voltage divider unit comprising:
• a plurality of third resistors, each having a resistance approaching the first resistance value;
• a plurality of fourth resistors connected in series between the output end of the first voltage divider unit and the output end of the second divider unit, each fourth resistor having a resistance approaching a second resistance value and both ends of each fourth resistor connected to two adjacent third resistors;
• and
• a plurality of control switches, each control switch comprising:
• a third switch connected between a third resistor and the first predetermined voltage;
• and
• a fourth switch connected between a third resistor and a second predetermined voltage;
• the signal converting method comprising:
• controlling the first switch and the second switch to electrically connect the first voltage divider unit to the first predetermined voltage, and to disconnect the second voltage divider unit from the first predetermined voltage, and controlling the plurality of control switches for the output end of the second divider unit generating a first voltage approaching the analog input signal, and controlling the successive approximation register generating a first digital bit stream according to the first voltage;
• controlling the first switch and the second switch to disconnect the first voltage divider unit from the first predetermined voltage, and to electrically connect the second voltage divider unit to the first predetermined voltage, and controlling the plurality of control switches for the output end of the first divider unit generating a second voltage approaching the analog input signal, and controlling the successive approximation register generating a second digital bit stream according to the second voltage;
• computing an average of the first digital bit stream and the second digital bit stream to generate the digital output signal.