Comparison of ultrasound baseband signal processors for use with an implantable controller.

The measurement of blood flow is an essential feature of a chronic implantable controller for the maintenance of metabolic parameters. Since ultrasound is a reliable measure of blood flow, its feasibility for chronic use is being studied. The device would require a low power, compact and simple signal processor. A comparison of eight baseband signal processors (frequency to voltage converters) was made in conjunction with four automatic gain control (AGC) modes. Since each processor was fundamentally different, they provided unique results to complex signals. In addition, the influence of amplitude modulation provided an additional component via the AGC.