Physical quantity change detection device which detects change by

Abstract

An object of the present invention is to provide an A/D conversion device capable of compensating for quantizing errors occurring as a result of variations in operating conditions and a physical quantity detection device using this A/D conversion device. In a physical quantity detection device, pulse signals CKA and CKB, having frequencies which change in response to a change in magnetic strength, are caused to be output from oscillators 16 and 18, with counter/decoder sections 22 and 24 generating, from each of these pulse signals CKA and CKB, pulse signals PA and PC, and a pulse signal PB having a phase difference with respect to pulse signal PA which varies in a prescribed manner in response to the oscillation frequency of oscillator 16, the phase difference between pulse signals PA and PC and the phase difference between pulse signals PA and PB each being quantized by a pulse phase difference encoding circuit 30, with the ratio DD (=DB/DD) between the quantized digital values DC and DB being determined by a divider 50, and a detection signal PO, which represents the magnetic change being detected from this value DD, being generated.