Cascode amp question - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues - primarily having to spend time purging garbage posts from the board. At some point I might start the RF Cafe Forums again if the phpBB software gets better at filtering spam.

Below are the old forum threads, including responses to the original posts.

-- Amateur Radio
-- Anecdotes, Gripes & Humor
-- Antennas
-- CAE, CAD, & Software
-- Circuits & Components
-- Employment & Interviews

-- Miscellany
-- Swap Shop
-- Systems
-- Test & Measurement
-- Webmaster

tse
Post subject: Cascode amp question Posted: Mon Sep 25, 2006 3:40 pm

Lieutenant

Joined: Mon Sep 25, 2006 1:51 pm
Posts: 1
Location: Titusville, Fl.
This amplifier is intended to produce fairly high voltage pulses (60V) with fast transitions (<3nS). It comes close (4-5nS) but looks like there is a loss of bandwidth in the cascode stage. When looking at the collector/emitter junction of the two transistors with a properly grounded scope probe one can see very narrow voltage spikes at the transitions of the pulses. I would expect to see only a DC voltage here. To me it looks like the emitter of the top transistor is presenting an inductive load that is causing the voltage spikes when the current changes rapidly. Does that make sense? Connecting the scope probe (8pF//10M ohm) to this junction also increases the output level when the input is a 150MHz square wave. Or when I connect a small cap from this junction to ground. Would some type of matching network at this juction help increase the bandwidth? Thanks for any help.

Posted 11/12/2012