Christian T. Wentz

An Area and Power-Efficient Analog Li-Ion Battery Charger Circuit

The demand for greater battery life in low-power consumer electronics and implantable medical devices presents a need for improved energy efficiency in the management of small rechargeable cells. This paper describes an ultra-compact analog lithium-ion (Li-ion) battery charger with high energy efficiency. The charger presented here utilizes the tanh basis function of a subthreshold operational transconductance amplifier to smoothly transition between constant-current and constant-voltage charging regimes without the need for additional area- and power-consuming control circuitry. Current-domain circuitry for end-of-charge detection negates the need for precision-sense resistors in either the charging path or control loop. We show theoretically and experimentally that the low-frequency pole-zero nature of most battery impedances leads to inherent stability of the analog control loop. The circuit was fabricated in an AMI 0.5-μm complementary metal-oxide semiconductor process, and achieves 89.7% average power efficiency and an end voltage accuracy of 99.9% relative to the desired target 4.2 V, while consuming 0.16 mm2 of chip area. To date and to the best of our knowledge, this design represents the most area-efficient and most energy-efficient battery charger circuit reported in the literature.

Optogenetics in psychiatric animal models

Optogenetics is the optical control of neuronal excitability by genetically delivered light-activated channels and pumps and represents a promising tool to fuel the study of circuit function in psychiatric animal models. This review highlights three developments. First, we examine the application of optogenetics in one of the neuromodulators central to the pathophysiology of many psychiatric disorders, the dopaminergic system. We then discuss recent work in translating functional magnetic resonance imaging in small animals (in which optogenetics can be employed to reveal physiological mechanisms underlying disease-related alterations in brain circuits) to patients. Finally, we describe emerging technological developments for circuit manipulation in freely behaving animals.