A calibratable switched-capacitor voltage reference and an associated calibration method are described. The voltage reference includes dynamic diode elements providing diode voltages, input capacitor(s) for sampling input voltages, base-emitter capacitor(s) for sampling one diode voltage with respect to a ground, dynamically trimmable capacitor(s) for sampling the one diode voltage with respect to another diode voltage, and an operational amplifier coupled to the capacitors for providing reference voltage(s) based on the sampled input and diode voltages and on trims of the trimmable capacitor(s). The voltage reference can be configured as a first integrator of a modulator stage of a delta-sigma analog-to-digital converter.

A delta-sigma modulator includes a quantizer, a signal propagation path including a plurality of cascaded integrators coupled between the input node and the quantizer, and a feedback network including a plurality of digital-to-analog converters. In a calibration mode of operation, a first digital-to-analog converter of the plurality of digital-to-analog converters of the feedback network receives a signal including a periodic alternated digital sequence, the first digital-to-analog converter being coupled to a first integrator of the plurality of cascaded integrators, integrators of the plurality of cascaded integrators other than the first integrator operate in a gain mode of operation, the delta-sigma modulator generates a digital test signal at an output of the quantizer based on the signal including the periodic alternated digital sequence, and calibration circuitry generates a calibration signal based on the digital test signal and a reference digital word.

Analog-to-digital converters (ADCs) can be used inside ADC architectures, such as delta-sigma ADCs. The error in such internal ADCs can degrade performance. To calibrate the errors in an internal ADC, comparator offsets of the internal ADC can be estimated by computing a mean of each comparator of the internal ADC. Relative differences in the computed means serves as estimates for comparator offsets. If signal paths in the internal ADC are shuffled, the estimation of comparator offsets can be performed in the background without interrupting normal operation. Shuffling of signal paths may introduce systematic measurement errors, which can be measured and reversed to improve the estimation of comparator offsets.

A time constant calibration circuit and method. The circuit comprises a resistor, a capacitor, an amplifier, a first switch and a second switch. The resistance of the resistor and/or the capacitance of the capacitor is variable. A first terminal of the resistor, a first terminal of the capacitor and a first input of the amplifier are coupled to a common node, which is coupleable to a reference current source. A second input of the amplifier is coupleable to a reference voltage. An output of the amplifier is coupled to a second terminal of the resistor and a second terminal of the capacitor. The circuit can perform a calibration process comprising one or more calibration cycles in which the switches route a reference current through the resistor in a first phase and through the capacitor in a second phase. The resistance and/or the capacitance is adjusted between calibration cycles.

A time constant calibration circuit and method. The circuit comprises a resistor, a capacitor, an amplifier, a first switch and a second switch. The resistance of the resistor and/or the capacitance of the capacitor is variable. A first terminal of the resistor, a first terminal of the capacitor and a first input of the amplifier are coupled to a common node, which is coupleable to a reference current source. A second input of the amplifier is coupleable to a reference voltage. An output of the amplifier is coupled to a second terminal of the resistor and a second terminal of the capacitor. The circuit can perform a calibration process comprising one or more calibration cycles in which the switches route a reference current through the resistor in a first phase and through the capacitor in a second phase. The resistance and/or the capacitance is adjusted between calibration cycles.

Reference scaling, op amp balancing and chopper stabilization techniques for delta-sigma modulators of analog-to-digital converters are provided. For reference scaling, unit elements in a feedback digital-to-analog (DAC) converter are driven by a reference voltage or disconnected from active circuitry to realize three DAC levels. While disconnected, the unit elements deliver no charge to the device which results in power saving and a reduction in thermal noise. Op amp balancing involves down-sampling the quantizer output followed by up-sampling on the feedback path and filtering to hold a DAC value of the signal for a duration of a sampling period to generate the feedback signal. Chopper stabilization is performed by chopping an operational transconductance amplifier of the integrator at a chopping frequency equal to the sampling frequency.

A sigma-delta analog-to-digital converter includes: a subtractor for subtracting a feedback signal from an analog input signal; a loop filter for processing the output signal from the subtractor to generate a filtered signal; a signal comparing circuit for selectively operating in an offset detection mode or a signal comparison mode, wherein the signal comparing circuit generates an error signal irrelevant to the relative magnitude between the filtered signal and a reference signal in the offset detection mode, and generates a comparison signal corresponding to the relative magnitude between the filtered signal and the reference signal in the signal comparison mode; an offset calibration control circuit for calibrating the offset of the signal comparing circuit and for controlling the signal comparing circuit to alternately switch between the offset detection mode and the signal comparison mode; and a digital-to-analog converter for generating the feedback signal according to the comparison signal.

A calibratable switched-capacitor voltage reference and an associated calibration method are described. The voltage reference includes dynamic diode elements providing diode voltages, input capacitor(s) for sampling input voltages, base-emitter capacitor(s) for sampling one diode voltage with respect to a ground, dynamically trimmable capacitor(s) for sampling the one diode voltage with respect to another diode voltage, and an operational amplifier coupled to the capacitors for providing reference voltage(s) based on the sampled input and diode voltages and on trims of the trimmable capacitor(s). The voltage reference can be configured as a first integrator of a modulator stage of a delta-sigma analog-to-digital converter.

A calibratable switched-capacitor voltage reference and an associated calibration method are described. The voltage reference includes dynamic diode elements providing diode voltages, input capacitor(s) for sampling input voltages, base-emitter capacitor(s) for sampling one diode voltage with respect to a ground, dynamically trimmable capacitor(s) for sampling the one diode voltage with respect to another diode voltage, and an operational amplifier coupled to the capacitors for providing reference voltage(s) based on the sampled input and diode voltages and on trims of the trimmable capacitor(s). The voltage reference can be configured as a first integrator of a modulator stage of a delta-sigma analog-to-digital converter.

A calibratable switched-capacitor voltage reference and an associated calibration method are described. The voltage reference includes dynamic diode elements providing diode voltages, input capacitor(s) for sampling input voltages, base-emitter capacitor(s) for sampling one diode voltage with respect to a ground, dynamically trimmable capacitor(s) for sampling the one diode voltage with respect to another diode voltage, and an operational amplifier coupled to the capacitors for providing reference voltage(s) based on the sampled input and diode voltages and on trims of the trimmable capacitor(s). The voltage reference can be configured as a first integrator of a modulator stage of a delta-sigma analog-to-digital converter.