As a Low - Input - Impedance Preamplifier for Current - Division Use

By grounding the usual inputs of a 733 amplifier chip and driving one of the gain-control pins, one obtains a common-base input stage with an input impedance of about 20 ohms. This can be used as an inexpensive current-division preamp and, in large multichannel systems, will probably not limit the performance. In the current-division method of coordinate measurement one observes the (integrated) current pulses coming from each end of the sense wire of a proportional chamber. The position (along the wire) is proportional to the measured asymmetry of these pulses. Accuracy is limited by electronic noise. The preamp must have an input impedance which is small compared with the sense wire resistance. Considerable effort has gone into the design of low-noise, low-input-impedance preamps, which when combined with optimal filtering give excellent position resolution (< 10m3> in small detector systems, such as magnetic spectrometer focal plane detectors. The literature1 is rather heavily weighted towards such detectors, which usually have a single sense wire, are used to detect particles well above min-i, and permit one to lavish care on the design