Reduction in signal intensity of a harmonic component included in an output of a delta-sigma modulator is suppressed. A signal processing device includes: a delta-sigma modulator 11 that outputs a pulse signal; a first processor 12 that generates, from the pulse signal P.sub.O outputted from the delta-sigma modulator 11, a discontinuous pulse signal P.sub.C in which each of one-pulse sections in the pulse signal P.sub.O has a low level region on at least one of a rear end and a front end of the one-pulse section; and a second processor that generates a short-width pulse signal P.sub.S having a pulse width shorter than a pulse width of the discontinuous pulse signal P.sub.C generated by the first processor 12.

A measuring circuit includes a dither tone generator circuit and a digital signal processing circuit. The dither tone generator circuit generates a dither tone, and injects the dither tone to a delta-sigma analog-to-digital converter that is offline. The digital signal processing circuit processes a digital output of the delta-sigma analog-to-digital converter with the dither tone injected, to generate a Q-factor measurement result of a resonator-based loop filter included in the delta-sigma analog-to-digital converter.

The systems and methods discussed herein related to analog to digital conversion. An apparatus can include an analog to digital converter including a loop circuit and a comparator circuit. The apparatus can also include a first circuit configured to provide comparator offset calibration for the comparator circuit and a second circuit configured to provide loop calibration for the loop circuit.