A variable gain front-end electronics for drift chambers

The cluster counting/timing technique in a drift chamber allows to have a bias free impact parameter estimate. The application of this technique requires to measuring and counting the arrival times of each individual ionization cluster to a sense wire. In a Helium based gas mixture the rise time of the signal from a cluster is approximately 1 ns, therefore a readout electronic front-end with high linearity, low distortion and sufficiently high bandwidth is required. Furthermore, it would be useful for the readout electronics to be able to easily adapt its gain to the detector’s operating point. The use of a variable gain amplifier (VGA) allows to meet the needs arising from the changed operating conditions of the detector. The market offers components capable of satisfying all these needs with dimensions compatible with high-density drift chambers. A high linear, low distortion, remotely controllable, about 1GHz bandwidth and compact VGA is presented together with the measurements performed.