Low Noise, Low Power Sensor Interface Circuits for Spectroscopy in Standard CMOS Technology Operating At 4 K

摘要

In the framework of the Photodetector Array Camera and Spectrometer (PACS) project (for the European Herschel Space Observatory) IMEC designed the Cold Readout Electronics (CRE) for the Ge:Ga far-infrared detector array. Key Specifications for this circuit were high linearity (3%), very low power consumption (80 microwatts for an 18 channel array), and very low noise (200 e) at an operating temperature of 4.2K (LHT-Liquid Helium Temperature). We have implemented this circuit in a standard CMOS technology (AMIS 0.7micrometers), which guarantees high production yield and uniformity, relatively easy availability of the technology and portability of the design. However, the drawback of this approach is the anomalous behavior of CMOS transistors at temperatures below 30-40K, known as kink and hysteresis effects and under certain conditions the presence of excess noise. These cryogenic phenomena disturb the normal functionality of commonly used circuits or building blocks. We were able to overcome these problems and developed a library of digital and analog building blocks based on the modeling of cryogenic behavior, and on adapted design and layout techniques. These techniques have been validated in an automated cryogenic test set-up developed at our institute. We will present here in detail the full design of the 18 channel CRE circuit, its interface with the Ge:Ga sensor, and its electrical performance, and demonstrate that all major specifications at 4.2 K were met. We will equally present the techniques used to integrate and validate the circuit for its use at these extremely low temperatures. Other designs and topologies for low noise and low power will also be presented.