Single photon imaging X-ray spectrometers using low noise current preamplifiers with dc voltage bias

Abstract

We have developed superconducting single-photon imaging x-ray detectors with an energy resolution of 54 eV at 6 keV and a spatial resolution of 1 pm over an effective length of 40 pm. They utilize a current-sensitive low-noise preamplifier with a dc voltage bias. It has a signal bandwidth of 300 kHz, current noise of i = 0.26 pA/-\IHz and voltage noise of e, = 0.5 nV/?Hz with an input capacitance of 200 pF under operating conditions. Injected pulses with a charge Q = 3.7*106 electrons have been measured with a standard deviation OQ = 3400 electrons, corresponding to an electronic noise of 13 eV at 6 keV.

Diffusion-Engineered Quasiparticle Multiplication for STJ Single Photon Detectors

“…We add extra circuitry that allows the A250/2SK146 composite amplifier to be DC coupled and provide an active voltage bias to the junctions [10]. The STJ devices studied had a 100 junction and a Ta absorber; the Ta plug was the same thickness, 545 nm, as the absorber.…”

Preamplifier development for superconducting tunnel junction array X-ray detector electronics

“…Using these methods, we fabricated and optimized four preamplifier designs and then compared them to the "LLNL" preamplifier currently used on the 36 element STJ array at the ALS [5][6][7]9]. Our lowest noise variants for these designs are reported in Table II.…”

“…1 shows the class of topologies we investigated, which, contrary to designs for semiconductor detectors, are transimpedance amplifiers with Rf of order 1 Mȍ to satisfy our input impedance requirement. The control loop used to hold the bias point follows Friedrich's earlier design [9], with the addition of a serial DAC and low pass filter to remotely control the loop's set point. source stabilized mode both with Q3 and by directly tying Rcb to Q1's source.…”

New Developments in Superconducting Tunnel Junction X-Ray Spectrometers for Synchrotron Science

“…For low noise we use a composite preamplifier with two BF862 JFETs in parallel at the input with a total transconductance g m = 45 mS and a voltage noise of 0.8 nV/ √ Hz. A second feedback loop senses the STJ bias set point and adjusts the JFET bias current to keep its gate voltage at the desired level [5]. The low-cost requirement can be met by replacing the expensive A250 opamp used in current STJ preamps with a $3.50 AD829 [6].…”