Complimentary my dear Watson ...... hi
G..
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From: "James Moritz" <[email protected]>
Sent: Monday, August 01, 2011 12:48 AM
To: <[email protected]>
Subject: Re: LF: frequency doubler and divider
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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