Integrating analog to digital converter with improved resolution

A method of converting an input analog signal into an output digital signal, the method comprising:

• applying the input analog signal to an integrator for a period of time;
• applying a reference signal to the integrator to return the voltage at the integrator output to an original value, wherein the original value is zero;
• counting clock cycles during said applying the reference signal to determine a primary slope count value;
• measuring a first integrator output voltage before a zero crossing and a second integrator output voltage after the zero crossing;
• determining a fractional slope count as a percentage of a clock cycle time period before the zero crossing;
• calculating a total slope count, wherein the total slope count includes the primary slope count value and the fractional slope count value;
• and
• determining the input analog signal using the total slope count value.

An analog to digital converter for converting an input analog signal into an output digital signal, comprising:

• an integrator operable to integrate the input analog signal for a first period of time, wherein the integrator is operable to receive a reference signal to return the integrator to an original value corresponding to a value prior to integrating the input analog signal;
• a processor coupled to an output of the integrator for counting clock cycles while the reference voltage is applied to determine a primary slope count value;
• a residue analog to digital converter coupled to the output of the integrator for measuring the voltage at the integrator output two or more times while the reference signal is applied;
• wherein the processor is operable to determine a fractional slope count using the measured two or more integrator voltages to compute the fractional slope count occurring before the return of the voltage at the integrator output to the original value;
• wherein the processor is further operable to calculate a total slope count including the primary slope count value and the fractional slope count value;
• and
• wherein the processor is further operable to determine the input analog signal using the total slope count value.

A method of converting an input analog signal into an output digital signal, the method comprising:

• applying said input analog signal to an integrator over one or more time intervals to produce an integrated output signal, the integrated output signal being positive for a number of said time intervals corresponding to a positive slope count and negative for a remaining number of said time intervals corresponding to a negative slope count;
• applying a reference signal to the integrator to return the integrator to an original value corresponding to a value prior to integrating the input analog signal;
• measuring the integrator output voltage two or more times during said applying the reference signal;
• determining a fractional slope count using the measured two or more integrator output voltages to compute the fractional slope count corresponding to the return of the integrator to the original value;
• calculating a total slope count including the positive and negative slope count values and the fractional slope count value;
• and
• determining the input analog signal using the total slope count value.

A multi slope analog to digital converter for converting an input analog signal into an output digital signal, comprising:

• an integrator operable to integrate the input analog signal for a first period of time, wherein the integrator includes an input which is operable to selectively receive one or more of the input analog signal, a positive reference signal, or a negative reference signal, wherein the integrator produces an integrated output signal, the positive reference signal being applied to the integrator for a number of time intervals corresponding to a positive slope count and the negative reference signal being applied to the integrator for a remaining number of said time intervals corresponding to a negative slope count;
• a processor coupled to an output of the integrator for determining a positive slope count value and a negative slope count value;
• a residue analog to digital converter coupled to an output of the integrator for measuring the integrator output voltage two or more times while the reference signal is applied;
• wherein the processor is operable to determine a fractional slope count using the measured two or more integrator output voltages to compute the fractional slope count occurring before the return of the integrator to an original value corresponding to a value prior to integrating the input analog signal;
• wherein the processor is further operable to calculate a total slope count including the positive and negative slope count values and the fractional slope count value;
• and
• wherein the processor is further operable to determine the input analog signal using the total slope count value.

A method of converting an input analog signal into an output digital signal, the method comprising:

• a) applying the input analog signal to an integrator for a current interval;
• b) applying a reference signal to the integrator to return the integrator to an original value corresponding to a value prior to integrating the input analog signal;
• c) measuring the integrator output voltage two or more times during said applying the reference signal;
• wherein a first fractional slope count was determined in a prior interval immediately before the current interval, wherein the first fractional slope count indicates a deviation of the integrator from a reference value at the beginning of the current interval;
• d) determining a second fractional slope count during a subsequent interval immediately after the current interval, wherein the second fractional slope count indicates a deviation of the integrator from a reference value at the end of the current interval;
• e) determining a fractional slope count for the current interval based on the first and second fractional slope counts;
• f) repeating said steps a)-e) one or more times;
• and
• g) filtering the fractional slope counts for a plurality of intervals to produce the output digital signal.

A method of converting an input analog signal into an output digital signal in a sigma delta converter, wherein the sigma delta converter receives a reference voltage and the input analog signal in a time multiplexed fashion, the method comprising:

• a) applying the input signal to an integrator to integrate the input analog signal for a current interval;
• b) applying a reference signal to the integrator to return the integrator to an original value corresponding to a value prior to integrating the input analog signal during a ramp-down interval after the current interval, wherein the input signal is not applied to the integrator during the ramp-down interval;
• c) measuring the integrator output voltage two or more times during said applying the reference signal;
• wherein a first fractional slope count was determined in a prior interval immediately before the current interval, wherein the first fractional slope count indicates a deviation of the integrator from a reference value at the beginning of the current interval;
• d) determining a second fractional slope count during a subsequent interval immediately after the current interval, wherein the second fractional slope count indicates a deviation of the integrator from a reference value at the end of the current interval;
• e) determining a fractional slope count for the current interval based on the first and second fractional slope counts;
• f) repeating said steps a)-e) one or more times;
• and
• g) filtering the fractional slope counts for a plurality of intervals to produce the output digital signal.

A method of converting an input analog signal into an output digital signal in a sigma delta converter, wherein the sigma delta converter receives a reference voltage and the input analog signal in a time multiplexed fashion, the method comprising:

• a) applying the input signal to an integrator to integrate the input analog signal for a current interval;
• b) applying a reference signal to the integrator to return the integrator to an original value corresponding to a value prior to integrating the input analog signal during a ramp-down interval after the current interval, wherein the input signal is not applied to the integrator during the ramp-down interval;
• c) determining a slope count during said applying the reference signal, wherein the slope count indicates whether a positive or negative reference was applied during the interval;
• d) repeating said steps a)-c) one or more times;
• and
• e) filtering the slope counts for a plurality of intervals to produce the output digital signal.