A wideband PWM-FSK receiver for wireless implantable neural recording applications

We have custom designed a wideband receiver for wireless implantable neural recording (WINeR) systems that use pulse width modulation and frequency-shift-keying (PWM-FSK) to wirelessly transmit neural signals across a short distance (lm). The receiver consists of a 50 MHz ~ 1 GHz down-converter, FSK & PWM demodulators, and a USB interface. The receiver also digitizes the incoming samples using a 16-bit high speed emitter- coupled logic (ECL) counter running at 800 MHz, and sends a continuous stream of data frames to a PC in real-time. Finally a custom developed Visual C++ software on the PC acquires the samples, time-division demultiplexes them, and shows them in real-time. The receiver is bench-top tested wirelessly with a 4- channel WINeR transmitter. Measurements show that the entire system input referred noise with this receiver is ~11.4 muV_rms, which is equivalent to 8 bits of resolution at 500 ksample/s.