Development of an octal CMOS ASD for the ATLAS Muon detector
Development of an octal CMOS ASD for the ATLAS Muon detector
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为 ATLAS Muon 探测器开发八进制 CMOS ASD
DOI：
10.5170/cern-1999-009.436
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发表时间：
1999
期刊：
影响因子：
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通讯作者：
C. Posch
中科院分区：
文献类型：
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作者：
J. Huth;J. Oliver;J. Shank;E. Hazen;C. Posch
介绍了ATLAS μ子探测器CMOS放大器/整形器/整形器的研制。第一阶段的工作是在HP 0.5μm n阱CMOS中制作一个简化的4沟道器件（ASD-lite），工作电压为3.3V。高度精确的DC模型产生了与SPICE预测密切匹配的性能。片上串扰，一个不容易模拟的参数，被测量为低于0.5%。芯片的测量和室内测试的结果将提交。该设备将用于ATLAS MDT（平行漂移管）模块的早期测试。最后八进制MDTASD，这将是完全可编程的，包括威尔金森前沿电荷测量的进一步工作，将提交。μ子谱仪的目标是对1 TeV μ子的PT分辨率为10%。这意味着单线分辨率要求<80μm。平均漂移速度约为20μm/ns，这意味着单个管的系统定时误差约为500 ps。为了避免老化问题，计划的气体增益很低，约为2 × 10 - 4。预期的信号（收集的电荷）大约是每个初级电子1500个电子（0.25fC），因此良好的位置分辨率需要低噪声前端。在分辨率和稳定性方面，15 ns的指定前置放大器峰值时间是一个很好的折衷。通道间串扰规定小于1%。高达400 kHz/线的高计数率以及长电子漂移时间需要双极整形方案或有源基线恢复，以避免由于基线波动而导致的分辨率下降。在TDR时，基线MDT气体为Ar/N2/CH 4 91/4/5（3巴绝对压力），其线性度非常高，最大漂移时间为500 ns。ASD整形方案的选择是单极整形和主动基线恢复，原因如下。首先，它允许测量信号后沿，其具有相对于聚束交叉的固定延迟，精度约为20 ns。其次，它避免了每个μ子轨道的多个阈值交叉，这将增加命中率，从而增加读出占用率。所有含碳氢化合物的MDT气体的老化问题导致基线气体变为Ar/CO2 93/7（3巴绝对压力），其最大漂移时间为800 ns，并且非常非线性。长漂移时间和非线性使后沿分辨率降低到约80 ns，并且即使对于单极整形方案也会导致多个阈值交叉。因此，我们采用了双极性整形方案，因为它不需要有源BLR，也不需要可编程滤波器时间常数。为了避免来自单个信号的多个阈值交叉的多个命中，我们引入等于最大漂移时间的固定死区时间。结果表明，死区时间的总体增加不会导致模式识别效率的降低。ADC将在阈值跨越时间之后测量20 ns栅极中的信号电荷。然后用通常的威尔金森技术将电荷编码成脉冲宽度。该信息允许通过执行时间回转校正来提高分辨率。此外，它还可用于诊断和监测目的，也可用于dE/dx识别缓慢移动的重粒子，如重μ子SUSY伙伴。将提供两种操作模式。在一种模式下，ASD输出给出超过阈值信息的时间，即信号前沿和后沿定时。另一种模式测量前沿时间和电荷，被视为默认操作模式。ATLAS MDT系统由大约350，000个直径为3cm的加压漂移管组成，长度从1.5米到6米不等。MDT的一端由ASD读出，另一端端接于管的特性阻抗（380Ω）。前置放大器的输入阻抗相对较低，约为100Ω，以最大限度地提高收集的电荷。为了最大限度地降低成本，MDT信号在两层“刺猬板”上传输到夹层板，夹层板包含24个读出通道：3个八通道ASD，一个24通道TDC和相关的控制电路。单个MDT室可具有多达432个漂移管或18个hedgehog/夹层板
Development of a CMOS amplifier/shaper/ discriminator for the ATLAS Muon detector is presented. The first phase of this work has resulted in a simplified 4-channel device (ASD-lite) fabricated in HP 0.5μm n-well CMOS operating at 3.3 volts. Highly accurate DC models resulted in performance which closely matches SPICE predictions. On-chip crosstalk, a parameter not easily simulated, is measured to be below 0.5%. Results of chip measurements and on-chamber tests will be presented. This device will be used for early testing of ATLAS MDT (Monitored Drift Tube) modules. Further work on the final octal MDTASD, which will be fully programmable and include Wilkinson leading edge charge measurement, will be presented. Front End Requirements The Muon spectrometer aims for a PT resolution of 10% for 1TeV muons. This translates into a single wire resolution requirement of <80μm. The average drift velocity is about 20μm/ns, which implies a systematic timing error for an individual tube of about 500ps. The planned gas gain is low, about 2⋅10, to avoid aging problems. The expected signal (collected charge) is roughly 1500 electrons (0.25fC) per primary electron, so good position resolution requires a low noise front-end. A specified preamp peaking time of 15ns is a good compromise in terms of resolution and stability . The channel to channel crosstalk is specified to be less than 1%. The high count rates of up to 400kHz/wire together with the long electron drift times require either a bipolar shaping scheme or active baseline restoration to avoid resolution deterioration due to baseline fluctuations. At the time of the TDR the baseline MDT gas was Ar/N2/CH4 91/4/5 (3 bars absolute) which is very linear and has a maximum drift time of 500ns. The choice for the ASD shaping scheme was unipolar shaping with active baseline restoration for the following two reasons. First, it allows the measurement of the signal trailing edge , which has a fixed latency with respect to the bunch crossing, with an accuracy of about 20ns. Second, it avoids multiple threshold crossings per muon track, which would increase the hit rate and therefore the readout occupancy. Aging problems with all MDT gases containing hydrocarbons caused a change of the baseline gas to Ar/CO2 93/7 (3 bars absolute) which has a maximum drift time of 800ns and is very nonlinear. The long drift time and the non-linearity degrade the trailing edge resolution to about 80ns and cause multiple threshold crossings even for a unipolar shaping scheme. We therefore have adopted a bipolar shaping scheme since it does not require an active BLR and also does not require programmable filter time constants. To avoid multiple hits from multiple threshold crossings for a single signal we introduce a fixed dead time equal to the maximum drift time. It was shown that the overall increase in dead time does not cause a degradation of the pattern recognition efficiency. An ADC will measure the signal charge in a 20ns gate following the threshold crossing time. The charge is then encoded into a pulse width in the usual Wilkinson technique. This information allows a resolution improvement by performing a time slewing correction. Additionally, it is useful for diagnostics and monitoring purposes and might also be used for dE/dx identification of slow moving heavy particles like heavy muon SUSY partners. Two modes of operation will be provided. In one mode the ASD output gives the time over threshold information, i.e. signal leading and trailing edge timing. The other mode measures leading edge time and charge and is considered the default operating mode. Readout System Packaging The ATLAS MDT system consists of about 350,000 pressurized drift tubes of 3cm diameter, with lengths from 1.5 to 6m. The MDTs are read out by an ASD at one end, and the other end is terminated in the characteristic impedance of the tube (380Ω ). The preamp input impedance is a relatively low ~100Ω to maximize collected charge. To minimize cost, the MDT signals are carried on two-layer "hedgehog boards" to a mezzanine board, which contains 24 readout channels: 3 Octal ASDs, a single 24-channel TDC, and associated control circuitry. A single MDT chamber may have as many as 432 drift tubes or 18 hedgehog/mezzanine board