Low-noise and low-power pixel sensor chip for gas pixel detectors

Topmetal-M2 is a large-area pixel sensor chip fabricated using the GSMC 130 nm CMOS process in 2021. The pixel array of Topmetal-M2 consists of pixels of 400 rows × 512 columns with a pixel pitch of 45 μm × 45 μm. The array is divided into 16 subarrays, with pixels of 400 rows × 32 columns per subarray. Each pixel incorporates two charge sensors: a diode sensor and a Topmetal sensor. The in-pixel circuit primarily consists of a charge-sensitive amplifier for energy measurements, a discriminator with a peak-holding circuit, and a time-to-amplitude converter for time-of-arrival measurements. The pixel of Topmetal-M2 has a charge input range of0-3 k e-, a voltage output range of0-180 mV, and a charge-voltage conversion gain of59.56 μV∕e-. The average equivalent noise charge of Topmetal-M2, which includes the readout electronic system noise, is43.45 e-. In the scanning mode, the time resolution of Topmetal-M2 is 1 LSB = 1.25 μs, and the precision is ~ 7.41 μs. At an operating voltage of 1.5 V, Topmetal-M2 has a power consumption of49 mW∕cm2. In this article, we provide a comprehensive overview of the chip architecture, pixel working principles, and functional behavior of Topmetal-M2. Furthermore, we present the results of preliminary tests conducted on Topmetal-M2, namely, alpha-particle and soft X-ray tests.