Asynchronous successive approximation analog-to-digital conversion circuit

The invention provides an asynchronous successive approximation analog-to-digital conversion circuit comprising a sample hold circuit, an analog-to-digital conversion circuit, a first voltage comparing circuit, a first logic circuit and a pulse generating circuit, wherein the first voltage comparing circuit compares input signals in response to an effective level of a latch signal, and outputs a first logic level and a second logic level; the first logic circuit identifies a comparison result of the first voltage comparing circuit according to the first logic level and the second logic level in response of the effective level of an identification signal; the pulse generating circuit generates the latch signal and the identification signal, wherein the generation moments of the effective levels of the latch signal and the identification signal are independent from the first logic level and the second logic level. The asynchronous successive approximation analog-to-digital conversion circuit can eliminate the problem that the comparing circuit is incomplete caused by the metastable state problem of the comparing circuit, guarantee the precision of the asynchronous successive approximation analog-to-digital conversion circuit, and is easy to implement and low in cost.