A 32-Channel, Wide Dynamic Range Charge-Sensitive Readout Interface Circuit with an Improved Frequency Compensation Scheme for X-Ray Detection

To address the limited detection accuracy, narrow operating bandwidth, and complex structure of the charge readout circuits for photodiode arrays in an X-ray imaging system, a multi-channel charge-sensitive readout interface (ROIC) is proposed. By employing switched-capacitor circuits together with digital clock control technology, the ROIC samples the injected charges from 32 photodiodes and transfers them to a single voltage output sequentially. This design realizes multi-channel acquisition and single-channel output. The wide input range is achieved by tuning the gain of the charge-sensitive amplifier. This is accomplished by adjusting the integration feedback capacitor, which ranges from 0.5pF to 32pF. Meanwhile, to extend the gain-bandwidth product (GBW) of the core amplifier, the conventional Miller-capacitor compensation technique is replaced by three separate compensation capacitors, which further improves the overall stability. Simulation results show that the open-loop gain of the CSA amplifier is above 124dB. The GBW is larger than 2.6MHz. The channel non-linearity is 0.1% and the maximum gain error is 0.45%. Measurement results demonstrate the feasibility of the chip. The detector injunction capacitance can reach up to 60pF. It can drive a maximum load of 200pF. The chip power consumption is 43mW with a 5V supply.