Provided are an analog-to-digital (AD) converter, a sensor system, and a test system capable of reducing the time for test processing. AD converter includes input part, AD conversion part, first output part, and second output part. The analog signal output from sensor is input to input part. AD conversion part digitally converts an analog signal to generate first digital data and second digital data. First output part outputs the first digital data to control circuit. Second output part outputs the second digital data to test controller before first output part outputs the first digital data. In the test mode, test controller determines whether or not sensor system including sensor is in an abnormal state on the basis of the second digital data.

An integrated circuit includes a continuous time delta sigma analog-to-digital converter (CTDS ADC) and a test circuit for testing the CTDS ADC. The test circuit converts multi-bit digital reference data to a single-bit digital stream. The test circuit then passes the single-bit digital stream to a finite impulse response digital-to-analog converter (FIR DAC). The FIR DAC converts the single-bit digital stream to an analog test signal. The analog test signal is then passed to the CTDS ADC. The CTDS ADC converts the analog test signal to digital test data. The test circuit analyzes the digital test data to determine the accuracy of the CTDS ADC.

A quantizer for a sigma-delta modulator, a sigma-delta modulator, and a method of shaping noise are provided. The quantizer includes: an integrator configured to generate, in a K.sup.th sampling period, a quantization error signal for a K.sup.th period according to an internal signal, a quantization error signal for a (K−1).sup.th period, a filtered quantization error signal for the (K−1).sup.th period and a filtered quantization error signal for a (K−2).sup.th period; an integrating capacitor configured to store the quantization error signal for the K.sup.th period, to weight the internal signal in a (K+1).sup.th sampling period; a passive low-pass filter configured to acquire the quantization error signal for the K.sup.th period in a K.sup.th discharge period, and feed back the filtered quantization error signal to the integrator in a (K+1).sup.th sampling period and a (K+2).sup.th sampling period; and a comparator configured to quantize the quantization error signal for the K.sup.th period.

A method and an apparatus are provided for improving a carrier to noise density ratio (CNO) of a matched filter. A signal is received at a signal register of the matched filter. A local code is received at a local code register and a nulling register of the matched filter. An adder tree of the matched filter correlates the signal register and the local code register with respect to the nulling register to obtain a correlation result. The nulling register prevents high frequency samples of the signal register from affecting the correlation result.

An apparatus (7) for down-converting a sampled signal comprises a processing system (206) configured to apply a mixing-and-combining operation repeatedly to successive sub-sequences of N input samples, X, representative of a signal and having an initial sampling rate, M, to generate a sequence of output samples, Y, having an output rate, T, lower than the initial sampling rate M. The sub-sequences of the N input samples, X, are spaced at intervals that correspond to the output rate M. The mixing-and-combining operation generates a respective output sample Y from each sub-sequence, where Y depends on a set of products of the input samples X of the sub-sequence with respective values derived from a periodic mixing signal having a mixing frequency.

An oscillator provides a plurality of clock signals, including a first clock signal having a first frequency and a first period, wherein each clock signal has the first frequency and is phase shifted from the first clock signal by an integer times a predetermined fractional amount of the first period. A multiphase frequency divider receives the plurality of clock signals and provides a divided clock output, and includes an integer frequency divider which provides the divided clock output based on a modified clock input and a clock selector which provides a current clock as the modified clock input during a first portion of the divided clock output and a next clock as the modified clock input during a subsequent portion of the divided clock output. The next clock is selected from the plurality of clock signals based on a selected fractional phase shift amount indicated by a sigma-delta modulator.

A delta-sigma modulation circuit has a sampling period and, in operation, generates a delta-sigma modulated signal based on the analog input signal. The delta-sigma modulation circuit includes: a first integrator; an analog-to-digital converter; a feedback-loop coupled between an input of the first integrator and the output interface; a second integrator coupled between the first integrator and the analog-to-digital converter. The delta-sigma modulation circuit has loop-delay compensation circuitry having a plurality of switches. The loop delay compensation circuitry, in operation, controls the plurality of switches based on a time interval of a duration of half the sampling period and generates a loop-delay compensation signal.

A circuit includes a digital-to-analog converter (DAC) and a compensation circuit. The DAC has a first terminal and a second terminal. The compensation circuit has a third terminal and a fourth terminal. The third terminal is coupled to the first terminal, and the fourth terminal is coupled to the second terminal. The compensation circuit is configured to source current into the first terminal responsive to an increase in voltage on the second terminal, and to sink current from the first terminal responsive to a decrease in voltage on the second terminal.

A current to digital converter circuit has an integrator amplifier with an input adapted to receive a current signal and an output adapted to provide a voltage signal as a function of an integration of the current signal, a quantizer circuit with an input which is coupled to the output of the integrator amplifier and with an output adapted to provide a binary result signal as a function of a comparison of the voltage signal with at least a first reference voltage signal, a digital-to-analog converter circuit which is coupled in a switchable manner as a function of the binary result signal to the input of the integrator amplifier, and a controlled current source which is coupled to the output of the integrator amplifier via a first switch which is controlled as a function of the binary result signal such that an auxiliary current is supplied to the output of the integrator amplifier.

An oversampling filter oversamples a digital audio signal. A ΔΣ modulator delta-sigma modulates a signal output from the oversampling filter. A D/A converter converts a signal output from the ΔΣ modulator into an analog audio signal. The oversampling filter includes a processor configured to run firmware and a computational algorithm is configurable based on the firmware.