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Re: LF: frequency doubler and divider

To: <[email protected]>
Subject: Re: LF: frequency doubler and divider
From: "James Moritz" <[email protected]>
Date: Mon, 1 Aug 2011 00:48:09 +0100
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Dear Graham, Stefan, LF Group,

----- Original Message ----- From: "Graham" <[email protected]>


Has anyone  looked  closely  at  Jim's  Class  D/E  EER   tx ?

Well, Jim has ;-) All that is used is a limiting amplifier to "square up" the input sine wave. For a push-pull PA, anti-phase square wave gate drive is obtained simply using an inverter. There is no requirement to multiply or divide the frequency. To obtain a 50% duty cycle square wave, the limiting thresholds need to be symmetrical around the average value of the input waveform. In the EER transverter, I used a transistor differential pair to provide a well-defined symmetrical limited waveform. The output of the differential amp is fed through some CMOS gates to increase the gain and make the output "square-er". You could use a voltage comparator instead, but it has to be a fairly fast one to avoid significant asymmetry in the output waveform due to differences in rise/rall times with positive and negative going signals, and other effects.

This works fine provided your signal source generates a symmetrical waveform, i.e. the wanted signal frequency with or without odd order harmonics, such as a sine wave or a square wave. If the waveform is asymmetrical (containing substantial levels of even-order harmonics), such as a rectangular waveform with non-50% duty cycle, or contains non-harmonic components (e.g. unwanted mixing products), then a bandpass filter is needed to remove the unwanted components. But most practical signal generation schemes do not contain very high levels of unwanted frequency components close to the signal frequency, so a simple single LC tuned circuit with low Q is an adequate bandpass filter.

Cheers, Jim Moritz
73 de M0BMU




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