A digital control mechanism for the delay of a dual-microphone analog beamformer

The microelectronic industry is driven by the continuous demand for processing capabilities and performance. As such, most processing is performed nowadays in a digital fashion. Analog however is not to be neglected. A key feature in modern mixed-signal processing is wide-range tuning of the analog processing sections. One step forward is the implementation of digitally programmable analog. The aim of this paper is to illustrate the digital tuning mechanism on the analog beamformer of a dual-microphone array. Analog processing consists of having one microphone signal delayed by an allpass filter, in order to be synchronized to the other microphone signal. A Gm-C filter implementation was considered, and filter tuning was performed via the transconductor bias current. Digital control of the bias current was implemented with a current digital to analog converter, enabling a straightforward and simple control mechanism. Transistor-level simulation results validate the proposed design.