Toward VIP-PIX: A Low Noise Readout ASIC for Pixelated CdTe Gamma-Ray Detectors for Use in the Next Generation of PET Scanners

Abstract

VIP-PIX will be a low noise and low power pixel readout electronics with digital output for pixelated Cadmium Telluride (CdTe) detectors. The proposed pixel will be part of a 2D pixel-array detector for various types of nuclear medicine imaging devices such as positron-emission tomography (PET) scanners, Compton gamma cameras, and positron-emission mammography (PEM) scanners. Each pixel will include a SAR ADC that provides the energy deposited with 10-bit resolution. Simultaneously, the self-triggered pixel which will be connected to a global time-to-digital converter (TDC) with 1 ns resolution will provide the event's time stamp. The analog part of the readout chain and the ADC have been fabricated with TSMC 0.25 m mixed-signal CMOS technology and characterized with an external test pulse. The power consumption of these parts is 200W from a 2.5 V supply. It offers 4 switchable gains from ±10 mV/fC to ±40 mV/fC and an input charge dynamic range of up to ±70 fC for the minimum gain for both polarities. Based on noise measurements, the expected equivalent noise charge (ENC) is 65 e RMS at room temperature.

Simulation of the Expected Performance of a Seamless Scanner for Brain PET Based on Highly Pixelated CdTe Detectors

“…The digital part contains the time to digital converter (TDC), the digital controller, a configuration register, and the identification register. This solution is called “smart-pixel.” Its design, the development status, and the results of the successful characterization of the preliminary prototypes are described in detail in [10]. The “smart-pixel” has the advantage of compactness and of the robustness of having the analog front-end and the analog to digital conversion optimized for minimum parasitic loading and/or coupling.…”

“…The smart-pixel slow shaper integrates the deposited energy with 20 μ s peak time. After digitizing the peak value, the time needed to reset the pixel electronic before the next event is 130 μ s. The 150 μ s total signal processing time allows each channel to handle easily 6 kHz with negligible pile up [10]. To simulate the effect of the electronic measuring time and dead time, all energy depositions within the same voxel and within the first 20 μ s window time contribute to the total energy of a single hit; energies deposited right after and within the 130 μ s dead time, are lost.…”

“…The trigger defines the time stamp of the hit as measured by the TDC with 0.1 ns resolution. Additional smearing is considered due to the asymmetry between electron and hole mobilities [12] and to the jitter of the electronic discriminator as measured in [10]. A direct measurement of the coincidence time resolution [13] shows that for energy close to the 20 keV trigger threshold, a time coincidence window as wide as 20 ns is needed to detect at least 70% of the photon pairs.…”

A novel depth-of-interaction rebinning strategy for ultrahigh resolution PET

“…Recently, alternative directions have emerged based on semiconductor detectors, such as silicon, CdTe and CdZnTe (CZT), which allows excellent energy and spatial resolutions as well as detection efficiency (Gu et al 2011). There has been significant effort towards building ultrahigh resolution PET scanner using CdTe and CZT detectors (Matteson et al 2008, Yang et al 2012, Mitchell et al 2008, Morimoto et al 2011, Ueno et al 2009, Macias-Montero et al 2013, Yin et al 2014).…”

A 2D 4×4 channel readout ASIC for pixelated CdTe detectors for medical imaging applications

“…In Table I the original specifications of th electronics are listed [1]. Note that we spec equivalent noise charge (ENC) on the specifi discriminator is applied directly to the unfilt the pre-amplifier.…”