Patent ID: 8471752

Claim:
An A/D conversion apparatus comprising: an N-stage pulse circulating circuit comprising N (N is a natural number, N≧3) inverting circuits connected in a ring shape, the inverting circuits delaying an input pulse signal by a delay time corresponding to an amplitude of a separately input analog input signal, and outputting inverted pulse signals obtained by inverting the pulse signal; a counter unit that counts a number of circulations by which the pulse signal has circulated in the pulse circulating circuit within a predetermined time based on the inverted pulse signal output from one of the N inverting circuits; and a switching unit that switches an output destination of the inverted pulse signal, which is output from an inverting circuit of an M th (M is an odd natural number, 1≦M≦N−1) stage of the pulse circulating circuit, according to a change in an operation environment.