Design of an adjustable bias circuit using a single-sided CMOS supply for avalanche photodiodes

A charge pump circuit operating from a single-sided CMOS supply, capable of biasing avalanche photodiodes up to 40 V with load currents in the mA range is presented. This circuit introduces new design elements that overcome previously published limitations. These elements include pass-gate voltage regulators and a mechanism for linking the negative voltage regulator to the positive voltage output. This design allows linear adjustment of the output voltage from a single control voltage. The circuit has compact dimensions of 1.55 mm × 1 mm, including bond pads, which makes it suitable for hybrid integration in a single package with an APD and two surface-mount capacitors.

I. Introduction

Avalanche photodiodes are used in a wide range of lowlight sensing applications including astronomy [1], DNA sequencing [2], light detection and ranging (LIDAR) [3] and medical sensing [4]. Planar avalanche photodiodes (APDs) have been developed over a number of years that typically require bias voltages above 25 V [5], [6]. An integrable bias solution for these avalanche photodiodes was previously introduced in [7]. That circuit included a dual-rail charge pump to provide the high bias voltage and two shunt regulators to control the positive and negative outputs of the bias. The circuit is capable of sourcing rnA range load currents for shallow-junction planar APDs that operate up to 40 V. There are several drawbacks to this circuit approach. Firstly, two control voltages require adjusting by the end user to provide the required output voltage. Secondly, since the current divider in the shunt regulator is under high potential, a high-voltage process is required to ensure the stability of the circuit's operation, thereby adding cost to the chip fabrication process. Finally, a negative supply rail is needed to control the negative output, which adds to the complexity of the circuit.