Wideband flexible transmitter and receiver pair for implantable wireless neural recording applications

This paper presents a complete wideband 900 MHz wireless link with 75 MHz bandwidth consisting of an integrated flexible transmitter and a custom-designed receiver for wireless multichannel neural recording and biotelemetry applications. The transmitter is basically an LC-tank voltage controlled oscillator (VCO) with multiple tunable parameters. The hybrid tank consists of binary weighed PMOS varactors and a surface-mount (SMD) off-chip inductor, which also acts as an antenna to minimize the transmitter size. Taking advantage of two sets of PMOS varactors operating as three terminal devices, we were able to shift the VCO frequency-voltage (F-V) curve along the vertical axis by 16 MHz around its 920 MHz center frequency. We could also shift the VCO high gain region along the horizontal axis by 1.3 V, and finally change the VCO gain from 1.24 MHz/V to 23.8 MHz/V. The VCO was fabricated in the AMI-0.5 pm standard CMOS process and occupies 230 × 220 μm
²
. It draws 2.2 mA from ±1.5 V supplies. The receiver band can be tuned from 50 MHz to 1 GHz and its gain is adjustable from −14 to 21 dB. Using the SMD transmitter antenna, we received −53 dBm signal power in −100 dBm noise floor at the distance of 1 m with an 8.33 cm 1/4 λ monopole receiver antenna. Measurement results showed that when transmitting a 1 MHz square wave with 15 ns rising and falling edges across this wireless link, the received down converted signal has 10 ns delay and 20 ns frequency shifts.