Low Noise Preamplifier for Simultaneous High Resolution Energy & Time Measurement with Semiconductor Detectors

A new charge sensitive preamplifier permits state of the art timing with semiconductor detectors without compromising energy resolution. The compromises that are involved in previous methods of obtaining amplitude and time information are avoided by using a single input FET followed by fast, low noise circuitry. With the same input transistor the noise in the "energy" channel is the same to within a few per cent as for the best room temperature preamplifiers. There are two timing outputs. The faster of these is voltage sensitive and has a rise time of 2 nsec. The slower output, which is obtained from the output of the charge sensitive loop, has a rise time of less than 5 nsec for external input capacities up to 50 pF with 0.5 pF feedback capacitor. The leading edge response can be adjusted to approach an exponential function with a time constant as low as 6 nsec. This property is desirable when timing with thick detectors that have a fluctuating charge collection time, where it is necessary to trigger near the base line.