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Help - Need design info for Transistor Frequency Multiplier? - RF Cafe Forums

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RF Head
Post subject: Help - Need design info for Transistor Frequency Multiplier? Posted: Mon Jun 08, 2009 7:42 am

Captain

Joined: Mon Feb 09, 2009 12:26 pm
Posts: 11
Can anyone suggest any good source(s) for design information re: Transistor Frequency Multipliers?

In particular I need some information to help me build a frequency tripler with an output at around 900 MHz.

Steve


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nubbage
Post subject: Re: Help - Need design info for Transistor Frequency Multiplier?Posted: Tue Jun 09, 2009 2:57 am

General


Joined: Fri Feb 17, 2006 12:07 pm
Posts: 218
Location: London UK
Hi Steve
Sorry I cannot contribute any sources, but for what it is worth, my approach would be a conventional common emitter balanced amplifier using two transistors and a 3dB hybrid at 300MHz, then a resonant output balanced circuit at 900MHz. Over-driving the two bases will ensure plenty of third harmonic, and most of the second harmonic will cancel in the push-pull balanced amp.
Quantifying the level of 3rd harmonic, and how to design the input, output and biasing will require a text book or an article, but that is the fundamental approach I would look for.

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RF Head
Post subject: Re: Help - Need design info for Transistor Frequency Multiplier?Posted: Wed Jun 10, 2009 3:08 am

Captain

Joined: Mon Feb 09, 2009 12:26 pm
Posts: 11
That's definately worth considering. However, I only have a 2V5 supply rail and need to keep current as low as possible. On top of all this I have next to to design space!

I have tried a simple class C, CE stage with a simple resonator as the collector load. This is then light cap coupled out. Early results look promising.

I have also thought about approaching this as a harmonic termination problem. The idea being to pesent short circuits to the sub harmonics and an open circuit to the wanted 3F. End result should be square wave flavour and hence rich in 3F. First attempt was not great. Wait and see.

Steve


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nubbage
Post subject: Re: Help - Need design info for Transistor Frequency Multiplier?Posted: Wed Jun 10, 2009 6:45 am

General


Joined: Fri Feb 17, 2006 12:07 pm
Posts: 218
Location: London UK
Hi Steve
A series resonant circuit at 2*f is the approach used in varactor triplers too. In fact you might profit from using a 2GHz transistor in an unconventional way with no power supply, just using the collector base capacitance as a varactor, driving the base, and using a matching circuit between the collector and the output BPF at 3*f, then place a 2*f series resonant trap from collector to ground, with no supply at all. You save on space taken by supply choke, bias resistors, and decoupling cap.
See what happens. The loss might be 3dB but that is no big deal if you have enough drive power.
Let me know how it goes.

_________________
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