In the past decade, neuroscientists and clinicians have begun to use implantable MEMS multielectrode arrays (e.g., [1]) to observe the simultaneous activity of many neurons in the brain. By observing the action potentials, or "spikes," of many neurons in a localized region of the brain it is possible to gather enough information to predict hand trajectories in real time during reaching tasks [2]. Recent experiments have shown that it is possible to develop neuroprosthetic devices -machines controlled directly by thoughts -if the activity of multiple neurons can be observed.Currently, data is recorded from implanted multielectrode arrays using bundles of fine wires and head-mounted connectors; all electronics for amplification and recording is external to the body. This presents three major barriers to the development of practical neuroprosthetic devices: (1) the transcutaneous connector provides a path for infection, (2) external noise and interfering signals easily couple to the wires conveying weak neural signals (<500µV) from high-impedance electrodes (>100kΩ), and (3) the connector and external electronics are typically large and bulky compared to the ~5mm electrode arrays. To eliminate these problems, data from the implanted electrodes should be transmitted out of the body wirelessly. This requires electronics at the recording site to amplify, condition, and digitize the neural signals from each electrode. These circuits must be powered wirelessly since rechargeable batteries are relatively large and have limited lifetimes. Low power operation (<100mW) is essential for any implanted electronics as elevated temperatures can easily kill neurons.A wireless, fully-implantable neural recording system is being developed to facilitate neuroscience research and neuroprosthetic applications (see Fig. 30.2.

This paper reports a W-band solid-state power amplifier with an output power of 5.2W at 95 GHz and greater than 3 watts over the 94 to 98.5 GHz band. These SOA results were achieved by combining 12 GaN MMICs in a low-loss radial-line combiner network. The 12-way combiner demonstrates an overall combining efficiency of 87.5%, and excluding combiner conductor losses (0.3 dB), exhibits a combining efficiency of 93.7% at 95GHz. The size of the 12-way amplifier/combiner is only 2.39" dia. x 1.5" length. This work represents the first application of the radial-line combiner configuration to applications at W-band frequencies, and establishes new levels of performance for solid-state power amplifiers operating at these frequencies.