US Patent 7450678 Asynchronous signal input apparatus and sampling frequency conversion apparatus

In an asynchronous data input apparatus, a writing section writes data successively into a FIFO buffer memory at an variable input rate so that the data are accumulated in the FIFO buffer memory. A reading section reads the accumulated data successively from the FIFO buffer memory at an variable output rate so that the data amount residing in the FIFO buffer memory varies temporally. A detector detects a current data amount residing in the FIFO buffer memory, and a current direction of variation of the data amount residing in the FIFO buffer memory. A loop filter generates control information according to both of the detected current data amount and the detected current direction of variation of the data amount. A controller regulates the output rate according to the control information so as to promptly converge the current data amount residing in the FIFO buffer memory to a target data amount.