A 4096 Channel 50 Mc/S Servo-Stabilized Analogue-to-Digital Converter

Exploitation of the high resolution and wide energy range of semiconductor radiation detectors imposes severe demands on the linearity and stability of the associated A.D. C. system. A study has been made of various alternative conversion and stabilization schemes with particular reference to their use in a computer-based data gathering system. As a result of this study a 4096 channel 50 Mc/s servo-stabilized ramp converter has been developed. Stabilization is based on a bang-bang servo scheme, the ultimate reference being a mercury double pulse generator. A feature of the design is the ability to dial the energies defining the upper and lower limits of the range of interest. In this way the converter acts as its own window amplifier, always spanning the designated range with 4096 channels. In the design particular attention has been paid to factors affecting the system linearity. Notable among these has been the importance of transient thermal effects in the transistors, and the window expansion scheme which eliminates the problems associated with biased-off amplifiers.