" How are you supposed to know if a given transistor can handle class C operation at a given frequency? If you have to ask - the transisitor is probably not designed for that type of service. Normally any device intended for a class of service will have parameters decribing various classes of service and also present 'test circuits' for demonstrating same. I recommend viewing/getting ahold of some of the old Motorola "RF Device Data" books for a good feel on how the RF guys spec devices. If you're working with general 'switching' type transistors like the 2n2222a - these are not normally characterized for RF service - but function quite adequately for low power RF applications within their capability. It's the 'art' of RF design that enters here when devices are not fully characterized for service in RF apps (like 'S parameters', MUG, MAG, input and output Z at spot freqs, etc). Another choice for some apps requiring RF amps/oscillators are the family of products by www.minicircuits.com They publish an "RF/IF Designer's Guide" and sell "Designer's Kits" with an assortment of parts. A large part of RF design with discrete parts involves designing impedance matching circuits, designing for stability (amps that won't oscillate, etc) and the use of such RF Modeling Applications like Microwave Spice. It is not a trivial pursuit ... Jim (RF circuit design/test exper. from AM broadcast - Ku Band) ----- Original Message ----- From: "Sean Breheny" To: Sent: Monday, July 09, 2001 2:37 AM Subject: [EE]: Class C amps Hi all, In the midst of my research for the topics in my RF tutorial, I have found a question which really has me stumped and for which I can't find any answers anywhere. All the books on RF amplifier design say that class C RF amps should be operated with the transistor going fully between saturation and cutoff to maximize efficiency. This makes sense to me because you don't want the transistor conducting current AND having a significant voltage drop at the same time. What I don't understand, though, is this: when you design a transistor saturated switching circuit, you usually want to know the switching paramaters for the transistor (Ton, Toff, etc.) Yet, whenever I look up datasheets for RF power transistors intended for class C operation, no such parameters are given. What gives? How are you supposed to know if a given transistor can handle class C operation at a given frequency? I'm also puzzled as to why you never see Shottkey-clamped transistors in class C RF amplifier service, since that would surely allow class C operation at higher frequencies, wouldn't it? Thanks, Sean -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body