Coding method for digital to analog converter of a SAR analog to digital converter

A method for coding a successive approximation register analog to digital converter, comprising the steps of:

• sampling an input voltage;
• determining bit values for a first portion of a plurality of bits representing an output of the successive approximation register analog to digital converter using a thermometer coding technique, wherein the step of determining the bit values for a first portion of the plurality of bits further comprises the steps of:
• (a) switching capacitors associated with a bit from ground to a reference voltage;
• (b) determining whether a logical value of the bit is a first value or a second value;
• (c) if the logical value is the first value, switching capacitors associated with a next bit from the ground to the reference voltage;
• and
• (d) if the logical value is the second value, switching one-half of the capacitors associated with the bit currently connected to the reference voltage to ground;
• and
• determining bit values for a second portion of the plurality of bits representing the output of the successive approximation register analog to digital converter using a binary coding technique.

A method for coding a successive approximation register analog to digital converter, comprising the steps of:

• sampling an input voltage;
• determining bit values for each most significant bit of a plurality of bits representing an output of the successive approximation register analog to digital converter using a thermometer coding technique;
• determining bit values for each least significant bit of the plurality of bits representing the output of the successive approximation register analog to digital converter using the thermometer coding technique;
• and
• wherein transient errors are reduced since only one single switch is operated with respect to each bit value decision rather than two sets of switches generating transient noise to comparator inputs.

A successive approximation register analog to digital converter, comprising:

• a voltage comparator having first and second inputs and an output;
• a plurality of capacitors associated with a first group of bits connected to a first input of the voltage comparator, each of the capacitors having substantially a same value, a number of capacitors associated with each of the first group of bits doubling from a least significant bit of the first group of bits to a most significant bit of the first group of bit;
• and
• a controller configured to:
• (a) switch the capacitors associated with a bit from ground to a reference voltage;
• (b) determine whether a logical value of the bit is a first value or a second value;
• (c) if the logical value is the first value, switch capacitors associated with a next bit from the ground to the reference voltage;
• and
• (d) if the logical value is the second value, switch one-half of the capacitors associated with the bit currently connected to the reference voltage to ground.