Neural Dielet: A 0.4 mm$^{3}$ Battery-Less Crystal-Less Neural-Recording System on Die Achieving 1.6 cm Backscatter Range With 2 mm ×2 mm On-Chip Antenna

Miniaturization is essential in the design of wireless neural-recording systems. In recent years, the battery in neural-recording systems can be eliminated by wireless power transfer (WPT), while antenna and crystal become two main bottlenecks to minimize a battery-less neural implant. In conventional battery-less designs, the miniaturization of antenna led to a short communication range, and a crystal-less clock suffered from noise issue or power-hungry circuits. In this work, we demonstrate a 0.4 mm
$^{3}$
neural dielet, which is a battery-less crystal-less neural-recording system on die (SoD) within a 2 mm × 2 mm on-chip coil antenna. The communication range through the ultra-small antenna is extended by a proposed dither-based 3
$^{\text{rd}}$
-order intermodulation (IM3) technique, which prevents the backscatter communication from WPT blocker. Meanwhile, a dither-based 2
$^{\text{nd}}$
-order intermodulation (IM2) wireless-lock technique is proposed to remove the crystal. Measured results show that the SoD consumes 53.2
$\mu$
W power and achieves a wireless communication range of 1.6 cm at a bit-error rate (BER) of 8
$\times\, 10^{-6}$
, accompanied by simultaneous WPT for battery-less operation. In the animal experiment, the neural signal wirelessly recorded by our SoD in a battery-less way matches favorably with the wire-test results obtained by a commercial chip.