A digital conversion system including a sigma-delta converter, a tone generator that generates injects a tone signal into the conversion path of the sigma-delta converter at a frequency that is outside operating signal frequency range, a tone detector that isolates and detects a level of the injected tone signal and provides a corresponding tone level value, a tone ratio comparator that converts the tone level value into a tone level ratio and that compares the converted tone level ratio with an expected tone level ratio to provide an error signal, and a loop controller that converts the error signal to a correction signal to adjust a loop filter frequency the sigma-delta converter. Tones may be serially injected one at a time or simultaneously in parallel for determining a measured tone level ratio for comparison with a corresponding one of multiple stored expected tone level ratios.

A frequency ratio measurement device includes a counter section configured to count a time event of a first signal and output a count value obtained by multiplying the time event by k.sub.0, a time to digital converter section configured to output a time digital value corresponding to a phase difference between the first signal and a second signal, a combiner section configured to output a combined value of the count value and the time digital value, a subtractor section configured to output a difference value between a first value based on the combined value and a second value, a quantizer section configured to compare a third value based on the difference value with a predetermined threshold to thereby output a quantized value obtained by quantizing the third value, and a feedback section configured to output, based on a time event of the second signal, the second value based on the quantized value. The frequency ratio measurement device outputs, based on the quantized value, a delta-sigma modulated signal corresponding to a frequency ratio of the first signal and the second signal.

A frequency ratio measurement device includes a counter section configured to count a time event of a first signal and output a count value obtained by multiplying the time event by k.sub.0, a time to digital converter section configured to output a time digital value corresponding to a phase difference between the first signal and a second signal, a combiner section configured to output a combined value of the count value and the time digital value, a subtractor section configured to output a difference value between a first value based on the combined value and a second value, a quantizer section configured to compare a third value based on the difference value with a predetermined threshold to thereby output a quantized value obtained by quantizing the third value, and a feedback section configured to output, based on a time event of the second signal, the second value based on the quantized value. The frequency ratio measurement device outputs, based on the quantized value, a delta-sigma modulated signal corresponding to a frequency ratio of the first signal and the second signal.

Sigma-delta converters having a sampling circuit are provided. The sampling circuit is actuated such that sampling times are at least partially random.

Sigma-delta converters having a sampling circuit are provided. The sampling circuit is actuated such that sampling times are at least partially random.

An idle tone dispersion device outputs a frequency delta-sigma modulation signal obtained by using either one of a reference signal and a measured signal to perform frequency delta-sigma modulation of the other and dispersing an idle tone. The idle tone dispersion device includes n (n is any natural number equal to or larger than 2) frequency delta-sigma modulation sections and an adder configured to add up output signals of the n frequency delta-sigma modulation sections and output the frequency delta-sigma modulation signal. Each of the n frequency delta-sigma modulation sections uses either one of the reference signal and the measured signal to perform the frequency delta-sigma modulation of the other. At least one of the reference signal and the measured signal includes jitter including a frequency component higher than a frequency of an idle tone of an output signal of the frequency delta-sigma modulation section.

An idle tone dispersion device outputs a frequency delta-sigma modulation signal obtained by using either one of a reference signal and a measured signal to perform frequency delta-sigma modulation of the other and dispersing an idle tone. The idle tone dispersion device includes n (n is any natural number equal to or larger than 2) frequency delta-sigma modulation sections and an adder configured to add up output signals of the n frequency delta-sigma modulation sections and output the frequency delta-sigma modulation signal. Each of the n frequency delta-sigma modulation sections uses either one of the reference signal and the measured signal to perform the frequency delta-sigma modulation of the other. At least one of the reference signal and the measured signal includes jitter including a frequency component higher than a frequency of an idle tone of an output signal of the frequency delta-sigma modulation section.

According to an embodiment, a sensor circuit includes a sigma-delta analog to digital converter (ADC), a dithered clock coupled to the sigma-delta ADC, and a supply voltage circuit coupled to the sigma-delta ADC. The sigma-delta ADC is configured to be coupled to a low frequency transducer, and the dithered clock is configured to control of the sigma-delta ADC based on a dithered clock signal.

According to an embodiment, a sensor circuit includes a sigma-delta analog to digital converter (ADC), a dithered clock coupled to the sigma-delta ADC, and a supply voltage circuit coupled to the sigma-delta ADC. The sigma-delta ADC is configured to be coupled to a low frequency transducer, and the dithered clock is configured to control of the sigma-delta ADC based on a dithered clock signal.