Low-noise gallium-arsenide charge-sensitive preamplifiers for low-temperature particle detectors

Charge-sensitive preamplifiers for operation between 1 K and 120 K have been developed and evaluated. They use double-gate GaAs MESFETs selected for their low 1/f noise. These devices are operated with both gates interconnected, emulating single-gate MESFETs of double gate-length, obtaining in this way a value of A/sub f/, (the coefficient of the 1/f noise spectral power density), of 1.7*10/sup -13/ V/sup 2/ at 77 K and 3.8*10/sup -14/ V/sup 2/ at 4 K. The latter is one-fourth of the value exhibited by the original device before modification and two orders of magnitude less than the value measured at 300 K. At the optimum bias, operating point device transconductance is 6 mA/V and the power dissipation 360 mu W. The input capacitance is less than 5 pF, therefore H/sub f/, the 1/f noise characteristic parameter, is lower than 8.5*10/sup -25/ J and 1.9*10/sup -25/ J at 77 K and 4 K respectively. The basic circuit configuration consists of a double-cascade loaded with a bootstrapped current source. In this way, a high gain-bandwidth product is obtained despite the low dynamic output resistance, 3000 Omega , exhibited by the MESFETs at the operating point.<
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