A signal processor and method. The signal processor includes a signal current path. The signal processor includes a transconductor. The transconductor has an input operable to receive an input voltage of the signal processor. The transconductor also has an output operable to output a current based on the input voltage. The signal processor also includes a processing stage coupled to the output of the transconductor to receive and process the current outputted by the transconductor. The signal processor further includes a current replicator operable to generate a replica current proportional to the current outputted by the transconductor. The signal processor also includes a comparator operable to compare an output of the current replicator with a reference. The signal processor further includes a current limiter operable to limit the current outputted by the transconductor based on the comparison of the output of the current replicator with the reference.

Techniques are provided for phase coherent frequency synthesis. An embodiment includes a first phase accumulator to accumulate a frequency control word (FCW) at a clocked rate to produce a first digital phase signal representing phase data corresponding to phase points on a first sinusoidal waveform. The embodiment also includes a second phase accumulator to produce an incrementing reference count at the clocked rate and multiply it by the FCW to produce a second digital phase signal representing phase data corresponding to phase points on a second sinusoidal waveform. The multiplication is performed in response to change in the FCW. The embodiment further includes a multiplexer to select between the first and second digital phase signals based on completion of the multiplication. The embodiment also includes a phase-to-amplitude converter to generate digital amplitude data corresponding to the phase points on a sinusoidal waveform associated with the selected digital phase signal.

A photoelectric conversion apparatus includes a light receiving circuit configured to convert light into an electrical signal, a readout circuit configured to read out an analog signal corresponding to the electrical signal, a ΔΣ A/D converter configured to convert the analog signal into a digital signal, and a control circuit configured to change a gain of the photoelectric conversion apparatus in accordance with a change of a driving mode of the photoelectric conversion apparatus. The analog signal read out by the readout circuit is an analog current signal. The readout circuit includes a variable resistor on a signal path for supplying the analog current signal to the ΔΣ A/D converter. The control circuit changes the gain of the photoelectric conversion apparatus by changing a resistance value of the variable resistor.

A frequency delta-sigma modulation signal output circuit includes: a phase modulation circuit configured to generate n delay signals obtained by delaying a measurement target signal, n being an integer of 2 or more, and generate a phase modulation signal by randomly selecting one of the n delay signals in synchronization with the measurement target signal; and a frequency ratio digital conversion circuit configured to generate a frequency delta-sigma modulation signal using a reference signal and the phase modulation signal.

A phase locked loop comprises: a controllable oscillator 102; a variable divider arrangement 108, 110 which takes a signal from the controllable oscillator 102 and divides it by a variable amount to provide a lower frequency signal; a sigma-delta modulator 112 arranged to provide a control input to said variable divider arrangement 108, 110; and a phase detector triggered 104 by said lower frequency signal and a reference clock;
wherein said phase locked loop is arranged to be operable in a normal mode in which the controllable oscillator 102 is controlled by a voltage from said phase detector 104 and a calibration mode in which the controllable oscillator 102 is controlled digitally by a signal from a calibration module 114 which receives an input from said variable divider arrangement 108, 110.

A circuit includes a transistor, a signal generating circuit and a noise sensing circuit. The signal generating circuit is arranged to provide an input signal. The noise sensing circuit is coupled to the transistor and the signal generating circuit, and the noise sensing circuit is arranged for receiving the input signal provided by the signal generating circuit to generate an output signal to the transistor, wherein a signal component of the output signal generated by the noise sensing circuit cancels out a signal component of the input signal provided by the signal generating circuit, and the output signal and the input signal have opposite polarities.

A sub-ranging SAR ADC has a coarse flash ADC that generates bit values corresponding to MSBs of the digital output value, and a fine SAR ADC that generates bit values corresponding to LSBs of the digital output value. The fine ADC generates successive analog approximation signals for the analog input signal. Meta-stability (MTS) detection circuitry detects a coarse-ADC MTS condition in the coarse ADC if a magnitude of a difference between a current approximation signal and a previous approximation signal is greater than a specified threshold level. A controller controls operations of the sub-ranging ADC to correct for a detected coarse-ADC MTS condition. The MTS detection circuitry includes a positive MTS detector that detects a positive coarse-ADC MTS condition in the coarse ADC and a negative MTS detector that detects a negative coarse-ADC MTS condition in the coarse ADC.

The disclosure is directed to low-power high-resolution analog-to-digital converter (ADCs) circuits implemented with a delta-sigma modulators (DSMs). The DSM includes a single-bit, self-oscillating digital to analog converter (SB-DAC) and a dual-slope integrating quantizer that may replace an N-bit quantizer found in a conventional DSM. The integrating quantizer of this disclosure oscillates after quantization because the SB-DAC in the feedback path directly closes the DSM loop. The integrating quantizer circuit includes a switch at the input and two phases per sample cycle. During the first phase the switch sends an input analog signal to an integrator. During the second phase, the switch sends the feedback signal from the output of the self-oscillating SB-DAC to the integrator. The input to the SB-DAC may be output from a clocked comparator.

Provided is a modulation circuit that can correct an output state in real time and reliably modulate an input signal to output the modulated signal. The signal modulation circuit includes a subtractor, an integrator, a chopper circuit, a frequency divider, and a D-type flip-flop. A delay circuit of a sigma delta modulation circuit is not provided to a feedback circuit, and a signal is delayed and quantized in the D-type flip-flop. The chopper circuit inserts a zero level at timing synchronized with a clock signal, so that pulse density modulation is performed.

A built-in-self-test (BIST) circuit is connected to a processor and a sigma-delta modulator (SDM) and includes an averaging circuit, a reference signal generator, and a comparator. The averaging circuit calculates an average of a sum of a set of bit signals of the SDM output signal over a period of time period, and generates an average SDM signal. The reference signal generator generates a reference SDM signal based on an SDM input signal. The comparator compares the voltage levels of the average SDM and reference SDM signals with a threshold value, and generates a test output signal based on the comparison.