Introducing Timepix2, a frame-based pixel detector readout ASIC measuring energy deposition and arrival time

The Timepix2 ASIC (application-specific integrated circuit) is the upgraded successor to the Timepix [1] hybrid pixel detector readout chip. Like the original, Timepix2 contains a matrix of 65k square pixels of 55 μm pitch that can be coupled to a similarly segmented semiconductor sensor, or integrated in an ionising gas detector. The pixels are programmable, with several operation modes and selectable counter depths (up to 18 bits for time-of-arrival, ToA, and up to 14 bits for time-over-threshold, ToT). In ToT and ToA mode, each pixel records the arrival time and energy deposited by particles interacting with the corresponding sensor segment, with an optional separation of timing resolution for ToT and ToA: down to 10 ns each. The gain of the frontend circuit can be programmed to adapt to the quantity of energy deposited in the sensor, yielding a large dynamic range of 0.38 ke− to 950 ke−. The frontend noise in adaptive gain mode is 380 e− rms. The design also introduces some power optimisation features to the Timepix portfolio, such as power masking on selectable parts of the pixel matrix. With all pixels powered on, using 100 MHz for both ToT and ToA clock frequencies, and assuming a sparse particle interaction with the pixels, the matrix is estimated to consume less than 900 mW based on simulation.