A 40.68-MHz Fully-Integrated Voltage/Current-Mode Dual-Output PMU for Wireless Neural Implants

This paper presents a fully-integrated single-input dual-output power management unit operating both in voltage/current modes for powering mm-scale wireless neural implants. The chip operates in voltage mode most of the time, using an active full-wave rectifier to regulate a low-voltage, high-load output with high power efficiency and low output ripple ($<$32 $\mathrm{mV}_{\mathrm{pp}}$). It switches to current mode rectification when generating a high-voltage, low-load output. This dual-mode operation allows for flexible power distribution and configurable voltage ratios between the two outputs. The selected 40.68 MHz operating frequency reduces the required capacitances for input impedance matching and output filtering, enabling on-chip integration; the only external component is the receiver coil. A novel resonance breakup switch compatible with full-wave rectification ensures a smooth cold start-up of the chip without any external voltage supply. The chip was fabricated using 40-nm CMOS technology with an active area of 1.18 $\mathrm{mm^{2}}$ and was tested in a wireless power link. Measurement results demonstrate that the chip can simultaneously regulate two outputs, $V_{LV}$ = 1 V and $V_{HV}$ = 2 V, with a tested maximum output power of 10 mW and 32.6 µW on $V_{LV}$ and $V_{HV}$, respectively. At the optimal output power condition ($P_{LV}$ = 4.4$\sim$6.7 mW), the system achieves a peak power conversion efficiency of 85.87% and a peak end-to-end efficiency of 17.32% when regulating $V_{LV}$. The end-to-end efficiency drops by only 2.38% when regulating both outputs with $R_{LV}$ = 225 $\Omega$ and $R_{HV}$ = 400 k$\Omega$.