---- Dr Bruce Griffiths <[EMAIL PROTECTED]> wrote: > The RF amp IC's generally have inferior noise figures and reverse > isolation (20dB for RFIC, > 40dB for common base stage) than a well > designed discrete common base amplifier. In fact by stacking common base > amplifiers the reverse isolation can be made very high, at least at low > frequencies like 5MHz or 10MHz, without a severe impact on the noise > figure. HP used a dc coupled common base + common gate + common base > cascade in their 8554 RF signal generator. > NBS used cascaded common base stages in their high (120dB) reverse > isolation amplifiers. > If an OCXO buffer amplifier has poor reverse isolation then a variable > load impedance will have a measurable effect on the OCXO frequency. > > Bruce
Bruce, In cases where the output signal does not need to be a sinewave, how would a common base amplifier compare to a fast comparator and if necessary a digital buffer as necessary to deliver the necessary power level? If this is designed to drive a mixer, a square wave may actually be better than a sine wave (lower conversion loss), and I would venture that the isolation (at least load independence) in most comparators is much better than that of a monolithic amplifier. Didier _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
