Noise characteristics of bootstrapped photovoltaic and photoconductive detectors

摘要

Abstract: If linearity of a semiconductor photodetector is acritical issue in an application like in radiometry,spectrophotometry, etc. the detectors are used in theso called current measurement mode. In this mode thedetector is directly connected to a current-to-voltageconverter, consequently in an ideal situation all thephotogenerated charge carriers appear on the feedbackresistor of the converter and produce a voltage drop.Photovoltaic detectors are short circuited by theconverter, the built in electric field of the detectortransfers the generated carriers to the converter. Onthe other hand photoconductive detectors should bebiased externally by a constant voltage to produce aninternal field for the transport of the chargecarriers. Some applications need great area detectors,that especially in the IR wavelength region show lowshunt resistance values. Ge, InAs, InSb, PbS, PbSe,HgCdTe, etc., have many decades lower shunt resistancevalues than that of a Si or InGaAs detector operatingin the visible or near infrared region. If highsensitivity is needed than a high value of the feedbackresistor is required that decreases the closed loopgain, consequently the settling accuracy. Bootstrappingof the detectors virtually increases the shuntresistance and so restores the decreased closed loopgain and settling accuracy. The bootstrapping techniquewill be shown and the noise characteristics will beanalyzed and compared to the traditional solutions.!3