A Low-Power Asynchronous Step-Down DC–DC Converter for Implantable Devices

Abstract

In this paper, we present a fully integrated asynchronous step-down switched capacitor dc-dc conversion structure suitable for supporting ultra-low-power circuits commonly found in biomedical implants. The proposed converter uses a fully digital asynchronous state machine as the heart of the control circuitry to generate the drive signals. To minimize the switching losses, the asynchronous controller scales the switching frequency of the drive signals according to the loading conditions. It also turns on additional parallel switches when needed and has a backup synchronous drive mode. This circuit regulates load voltages from 300 mV to 1.1 V derived from a 1.2-V input voltage. A total of 350 pF on-chip capacitance was implemented to support a maximum of 230-μ W load power, while providing efficiency up to 80%. The circuit validating the proposed concepts was fabricated in 0.13- μm complementary metal-oxide semiconductor technology. Experimental test results confirm the expected functionality and performance of the proposed circuit.

Reference-Free Dynamic Voltage Scaler Based on Swapping Switched-Capacitors

“…Voltage converters are essential building blocks for many low power devices, such as biomedical devices, mobile phones, wireless sensor networks, energy harvesting devices, and internet-of-things (IoT) devices [1][2][3][4][5][6].…”

A Comprehensive Review on Rectifiers, Linear Regulators, and Switched-Mode Power Processing Techniques for Biomedical Sensors and Implants Utilizing in-Body Energy Harvesting and External Power Delivery

“…These converters are combinations of switches and capacitors where the charge is transferred from one capacitor to another under the control of regulator and switching circuitry [149]. In addition to being more immune to EMI, the inductor less design of SC converters can lead to a drastic reduction in the complexity and cost of the on-chip integration and fabrication process, and consequently, are widely employed in implant applications [150]- [152].…”

Concept Design for a 1-Lead Wearable/Implantable ECG Front-End: Power Management

“…Switched-capacitor (SC) DC-DC power converters are a suitable choice for these devices [ 5 , 6 ]. They require less die area overhead and are therefore low-cost and more compact than standard switched-mode power supplies.…”

“…During the last few years researchers and manufacturers have proposed a number of different solutions for smart power supply management (particularly power scavenging) systems that address the needs of power efficient biomedical devices. As a result, along with several proposed experimental/research devices (see [ 6 , 21 , 22 ] in Table 1 ), there are a plethora of off-the-shelf solutions available on the market. Unfortunately, the vast majority of these solutions are integrated power modules which, despite not requiring external components (use of small decoupling capacitors is often recommended), are big, bulky and often have an unregulated output and strict constraints for the input voltages.…”

“…A wide output voltage range is necessary for the wearable device and decent efficiency must be maintained in its various modes of operation. Unlike existing converters that are either small but cater for smaller power output [ 6 ], or can deliver much larger power but occupy much larger die area [ 22 ], a small, high power solution is very desirable for our proposed wearable application. Finally, a reconfigurable SC converter architecture is required in the power management solution to provide multiple conversion ratios and be able to deal with any changes to either the input voltage sourced by an energy-harvester and/or the output voltage required for a different mode of system operation (such as sleep, ECG measurement, data transmission).…”