DC-coupled Detectors Research Articles

High-speed tunable diode laser absorption spectroscopy for sampling-free in-cylinder water vapor concentration measurements in an optical IC engine

A novel, fiber-optic in situ laser hygrometer was developed to measure water vapor with microsecond time resolution directly inside an internal combustion (IC) engine. The instrument is intended for sampling-free quantification of recirculated exhaust gas in combustion engines. Direct tunable diode laser absorption spectroscopy was employed to allow absolute and self-calibrating H2O measurements. The compact and user-friendly instrument combines a fiber-coupled, 1.37 μm distributed feedback diode laser with kHz-fast, continuous wavelength scanning. Only small, typically 10 mm, optical access ports in the engine are needed. The new in situ hygrometer was tested via measurements in a motored optical research engine operated on ambient air, without any artificial humidification. Scanning the laser at 4 kHz resulted in a time resolution of 250 μs (i.e., 3° crank angle at 2,000 rpm), while the DC-coupled detector signals are digitized with a 4MSamples/s 16-bit data acquisition system. Absolute water vapor concentrations around 1 vol.% could be measured and quantified during the full compression stroke, i.e., over a pressure/temperature range of 0.07–0.52 MPa/300–500 K. Without any scan averaging or bandwidth filtering we could demonstrate signal-to-noise ratios between 51 (at p = 0.1 MPa) and 33 (at p = 0.4 MPa), which corresponds to H2O detection limits between 0.02 and 0.035 vol.% or length and bandwidth normalized detectivities of 285 and 477 ppb m Hz−½, respectively. Comparison of the dynamic H2O behavior during the compression stroke across several engine cycles and different operating conditions showed good reproducibility and absolute accuracy of the results, consistent with the boundary conditions, i.e., motored air operation. This new sensor therefore opens up new possibilities for engine cycle-resolved, calibration-free in situ AGR quantification and optimization in engine applications.

Low Noise 64-Channel ASIC for AC and DC Coupled Strip Detectors

A 64-channel ASIC (SXDR64) aimed to work with both AC and DC coupled detectors (Si, CdTe, GaAs), in a single photon counting mode with an energy window has been developed. Every channel of the ASIC consists of a charge sensitive amplifier, a pole-zero cancellation circuit, a 4th order shaper with programmable gain from 14 μV/e- to 50 μV/e- and peaking time from 115 ns to 380 ns, a base-line restorer, two independent discriminators, and two 20-bit counters. Control and readout of the chip are done using on-chip LVDS drivers/receivers. The ASIC can work with input leakage currents in the range from -10 nA up to 7 nA. The ENC obtained with an AC-coupled Si detector is 120 e- for a peaking time Tp=115 ns and Cdet=1.2 pF. With a DC-coupled CdTe detector, the ENC is 210 e- rms for a peaking time Tp=380 ns and Cdet=2 pF and the leakage current Idleak=0.15 nA. The implemented trim DACs at the discriminator inputs allows to minimize the effective threshold spread to 8 e- rms (at one sigma level). The ASIC is designed in a CMOS 0.35 μm technology and its total area is 4800×5000 μm2.

Comprehensive modeling of silicon microstrip detectors

In this work, the application of numerical device simulation to the analysis of high resistivity silicon microstrip detectors is illustrated. The analysis of DC, AC and transient responses of a single-sided, DC-coupled detector has been carried out, providing results in good agreement with experimental data. In particular, transient-mode simulation has been exploited to investigate the collection of charges generated by ionizing particles. To this purpose, an additional generation term has been incorporated into the transport equations; the motion of impact-generated carriers under the combined action of ohmic and diffusive forces is hence accounted for. Application to radiation tolerance studies is also introduced.