Surface plasmon resonance (SPR) sensor has been studied for high sensitivity optical biosensor as a single molecule
detection, virus detection, DNA sequencing etc. SPR sensor requires an ultra-small signal detection system that measures
very small intensity variation of reflected light along with the change of a refractive index near the sensor surface. In this
reason, lock-in detection method which is able to detect small signal buried in noise has been applied to SPR sensor. In
general lock-in detection method using multiplier and low pass filter measures DC value of output, and its sensitivity is
determined by 1/f noise at DC. Unlike the DC measurement we have proposed 2ω harmonic lock-in detection method
using multiplier and band pass filter. Sensitivity of the proposed lock-in detection method is much lower than 1/f noise at
DC. In this paper we will show that 2ω harmonic lock-in detection method for SPR sensor system providing the
sensitivity enhanced.
We present design of a front-end readout system consisting of charge sensitive amplifier (CSA) and pulse shaper
for detection of stochastic and ultra-small semiconductor scintillator signal. The semiconductor scintillator is double
sided silicon detector (DSSD) or avalanche photo detector (APD) for high resolution and peak signal reliability of
γ-ray or X-ray spectroscopy. Such system commonly uses low noise multichannel CSA. Each CSA in multichannel
includes continuous reset system based on tens of MΩ and charge-integrating capacitor in feedback loop. The high
value feedback resistor requires large area and huge power consumption for integrated circuits. In this paper, we
analyze these problems and propose a CMOS short pulse detection system with a novel CSA. The novel CSA is
composed of continuous reset system with combination of diode connected PMOS and 100 fF. This structure has
linearity with increased input charge quantity from tens of femto-coulomb to pico-coulomb. Also, the front-end
readout system includes both slow and fast shapers for detecting CSA output and preventing pile-up distortion.
Shaping times of fast and slow shapers are 150 ns and 1.4 μs, respectively. Simulation results of the CMOS
detection system for optical short-pulse implemented in 0.18 μm CMOS technology are presented.
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