Mos digital-to-analog converter employing scaled field effect devices

Abstract

A digital-to-analog driver capable of driving a speaker or other voice coil means and implementable using field effect semiconductor devices is disclosed. A plurality of switching field effect semiconductive constant current sources each having a control electrode and two current carrying electrodes are coupled in parallel at the current carrying electrodes thereof. Each switching field effect constant current sources preferably includes a field effect load device and a field effect switching device, the aforementioned control electrode preferably being the gate of the switching device. The respective width to length ratios of the active areas under the gates of the devices differ by a factor of two from each other. Therefore, the width to length ratio of the gates of a third one of the souces is twice the width to length ratio of the gates of a second one of the sources and four times the width to length ratio of the gates of a first one of the sources, and so forth. The gates of the switching devices receive the digital input signal and the resulting current flowing through the parallel coupled sources is a function of the magnitude of the digital signal applied to the gates of the switching devices. Preferably, the parallel coupled sources are coupled via a pair of switching devices to either side of a center tapped voice coil or speaker. Alternatively, embodiments using a center tapped transformer associated with the speaker and the embodiments not requiring a center tap are also disclosed.