Digital-to-analog converter.

摘要

A digital-to-analog converter comprises a sigma-delta modulator (4) for generating a 1-bit digital signal (D3) modulated synchronously with a clock signal (NFS) in response to a digital input signal (D2), which modulator is followed by a asynchronous analog sigma-delta modulator (6) for generating a bivalent asynchronously modulated signal (D4) in response to the synchronously modulated digital signal (D3). The information in the digital signal (D3) from the sigma-delta modulator (4) resides in signal transitions which can appear exclusively at discrete instants defined by the clock signal (NFS). The information in the asynchronously modulated signal (D4) from the asynchronous sigma-delta modulator is contained in an analog variation of the duty cycle. This means that the signal transitions of the asynchronously modulated signal (D4) are not tied to a fixed pattern of discrete instants but that all the intervening instants are also available. As a result of the freedom of the positions of the signal transitions the frequency spectrum of the asynchronously modulated signal (D4) has a substantially smaller width than the frequency spectrum of the synchronously modulated digital signal (D3) from the sigma-delta modulator (4). This enables the interface (16) with the further signal processing (8) to be simplified.