Design for a High-Duty-Cycle, Bipolar, Logarithmic Video Amplifier

摘要

The theoretical and practical aspects of a high-duty-cycle, bipolar, logarithmic, video pulse amplifier are described. The approximations to a logarithmic transfer function are reviewed. The realization of a logarithmic transfer function is accomplished by a cascade of transistorized feedback-pair stages utilizing feedback elements with exponential voltage-current characteristics. Both diode and transistor transconductance feedback are described. Practical bipolar and unipolar amplifier designs are presented. Both amplifiers have a duty-cycle capability of at least 15 percent and a video dynamic range of 100 DB. The deviation from a logarithmic response is less than plus or minus 0.5 DB and the noise figure is 11 DB. The rise time for a small-signal pulse is 0.2 microsecond and that for a large-signal pulse is 0.05 microsecond. (Author)