CDS circuit with BLA function for X‐ray CCD applications

Abstract

Correlated double sampling (CDS) circuits are essential to process the X-ray charge-coupled devices (CCDs) that have been used in the modern X-ray astronomical field. A novel CDS circuit is presented. The innovation of the circuit is that it greatly improves the noise and linearity performances through moving the clamping switch out of the signal path as well as omitting the sampling switch which eliminates the nonlinearity and thermal noise introduced by these switches. Also, a baseline adjustment (BLA) circuit is incorporated so as to make efficient use of the dynamic range of the ADC, making the CDS circuit flexible to interface the CCD operating under a wide range of temperatures. A prototype application-specific integrated circuit (ASIC) is designed with GlobalFoundries 0.35 μm CMOS process and the experimental results show that with pixel rate varying from 100 kHz to 1 MHz, the integral nonlinearity and equivalent input noise performances are quite consistent, which are better than 27 ppm and 23 μV, respectively, within a dynamic range of 1.5 Vpp. The effective adjustment range of the BLA is at least 2 V, and the power consumption for a single CDS core is 10 mW approximately from a 3.3 V power supply.