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Paul Burridge wrote in message . ..
What's a doubler based on the good old 1N4148 good for, top end frequency-wise? Thanks to Jan-Martin for his reference to some actual experiments. But in reply to Paul, I'd ask: Do you understand how the "full-wave rectifier doubler" works, basically? (Ideal waveforms and all that.) Do you have a data sheet for the 1N4148? What items from the data sheet do you suppose might limit the useful frequency? Can you make an estimate, based on the data sheet numbers? What would you do in a design to extend the frequency range for a given diode characteristic? For example, what does diode capacitance do to circuit operation? What does reverse recovery do? In the full-wave frequency doubler circuit, what does the input impedance look like, assuming an ideal transformer, when one diode is forward biased and the other is reverse-recovering? Can you think of parts to add to cause that to not be so much of a problem (assuming it is a problem)? Thinking about this sort of thing is useful not only in figuring out what to expect, at least ball-park, but also in getting better performance out of someone else's circuit and/or understanding its limitations. Cheers, Tom |
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On 22 Feb 2004 20:39:33 GMT, (Avery Fineman)
wrote: Sorry. If you are using the passive diode doubler looking like a full-wave rectifier circuit, and you have a symmetric square wave, the only harmonics you get are from the transition edges. Symmetric square waves have very low even harmonic energy content; harmonics are in the odd harmonic frequencies. A non-symmetric rectangular (not a 'square') waveform has more even-harmonic energy content. with some experience you might say something else. Even harmonics are 'harmonics' too and for many purposes it is an advantage when the odd harmonic content is low ---- Jan-Martin, LA8AK, N-4623 Kristiansand http://home.online.no/~la8ak/ |
Hmmm...I know that there are other ways to generate sampling pulses in
things like (ultra) fast sampling scopes. I suspect that similar techniques can be used for fast edges. What little I know about that area I can't really say much about. After my SRD posting, I reviewed a little more in the Inventions of Opportunity book. The late '50's fast sampling scope article mentioned that the HP Labs researcher who saw the diode recovery phenomenon went on to gain understanding about the mechanism involved, and presented a paper about it at one of the semiconductor conferences. A couple articles later in the book there's one devoted to SRDs. They show a *20 frequency multiplier in one stage using a SRD. Net efficiency can be pretty good, with the proper design. Just don't want to be actually dissipating the energy that's in all the other harmonics. Cheers, Tom Roy Lewallen wrote in message ... Tom Bruhns wrote: . . . . . . Seems like step recovery diodes are not in as great favor as they once were, since there are generally better ways to generate higher order harmonics. . . . Getting a bit off-topic here, but as of a few years ago, we were using step recovery diodes to generate the step in high speed TDR systems, and to generate the strobe for the sampling gate in high speed sampling scopes. Rise times were on the order of 7 - 15 ps (bandwidth up to 50 GHz or so), limited primarily by circuitry external to the diodes. SRDs replaced tunnel diodes in earlier generations of instruments. I've been out of touch with that class of instruments for a few years now -- do you know if something has replaced the SRD for generating fast steps, or just for harmonic generation? Roy Lewallen, W7EL |
Hmmm...I know that there are other ways to generate sampling pulses in
things like (ultra) fast sampling scopes. I suspect that similar techniques can be used for fast edges. What little I know about that area I can't really say much about. After my SRD posting, I reviewed a little more in the Inventions of Opportunity book. The late '50's fast sampling scope article mentioned that the HP Labs researcher who saw the diode recovery phenomenon went on to gain understanding about the mechanism involved, and presented a paper about it at one of the semiconductor conferences. A couple articles later in the book there's one devoted to SRDs. They show a *20 frequency multiplier in one stage using a SRD. Net efficiency can be pretty good, with the proper design. Just don't want to be actually dissipating the energy that's in all the other harmonics. Cheers, Tom Roy Lewallen wrote in message ... Tom Bruhns wrote: . . . . . . Seems like step recovery diodes are not in as great favor as they once were, since there are generally better ways to generate higher order harmonics. . . . Getting a bit off-topic here, but as of a few years ago, we were using step recovery diodes to generate the step in high speed TDR systems, and to generate the strobe for the sampling gate in high speed sampling scopes. Rise times were on the order of 7 - 15 ps (bandwidth up to 50 GHz or so), limited primarily by circuitry external to the diodes. SRDs replaced tunnel diodes in earlier generations of instruments. I've been out of touch with that class of instruments for a few years now -- do you know if something has replaced the SRD for generating fast steps, or just for harmonic generation? Roy Lewallen, W7EL |
In article , "Jan-Martin Noeding,
LA8AK" writes: On 22 Feb 2004 20:39:33 GMT, (Avery Fineman) wrote: Sorry. If you are using the passive diode doubler looking like a full-wave rectifier circuit, and you have a symmetric square wave, the only harmonics you get are from the transition edges. Symmetric square waves have very low even harmonic energy content; harmonics are in the odd harmonic frequencies. A non-symmetric rectangular (not a 'square') waveform has more even-harmonic energy content. with some experience you might say something else. Even harmonics are 'harmonics' too OK...I'll reset my time machine and do another 52 years in the business... :-) :-) :-) and for many purposes it is an advantage when the odd harmonic content is low Outside of a step-recovery diode multiplier for an L-band sampler-locked oscillator worked on about 1974 (oscillator at about 1.6 GHz), I've not found much even harmonic content from a symmetric square wave. Unsymmetric digital signals haven't been found to have much more even harmonic content than odd harmonit content when viewed on a spectrum analyzer...until the digital signal pulse width is VERY short compared to its repetition time. The SRD is able to get about as short as such pulses go and the duty cycle is in fractions of a percent. [also "avalanche diode" which I'm sure that someone will bring up sooner or later to start another argument...:-) ] The original question was about "practical multiplier stages." Those would range from doublers to quintuplers. Going much higher HAS been done but it takes VERY expensive lab instruments to prove them out, such as with an SRD "comb generator." Comb generators have all sorts of harmonics but trying to extract, say, the 21st without passing the 20th or 22nd harmonic requires a very fussy high-Q filter. Some of the things _possible_ are not quite in the homebrewer workshop category...or they take a LOT of time to complete. I mentioned the passive diode doubler for the simple reason it IS simple when used with a distorted sinewave source (not a square wave). The effect of the two diodes in a "full-wave rectifier like" circuit creates an artificial 2nd harmonic by adding one sinusoid swing with the other, opposite-polarity sinusoid swing inverted by transformer action. Jim Pennell commented on that previously (and quite correctly). That makes for a broadband, non-fussy doubler circuit. Old thing and not a super whiz-bang state-of-the- art, hot-off-the-drawing-board wonder but it works. :-) Len Anderson retired (from regular hours) electronic engineer person |
In article , "Jan-Martin Noeding,
LA8AK" writes: On 22 Feb 2004 20:39:33 GMT, (Avery Fineman) wrote: Sorry. If you are using the passive diode doubler looking like a full-wave rectifier circuit, and you have a symmetric square wave, the only harmonics you get are from the transition edges. Symmetric square waves have very low even harmonic energy content; harmonics are in the odd harmonic frequencies. A non-symmetric rectangular (not a 'square') waveform has more even-harmonic energy content. with some experience you might say something else. Even harmonics are 'harmonics' too OK...I'll reset my time machine and do another 52 years in the business... :-) :-) :-) and for many purposes it is an advantage when the odd harmonic content is low Outside of a step-recovery diode multiplier for an L-band sampler-locked oscillator worked on about 1974 (oscillator at about 1.6 GHz), I've not found much even harmonic content from a symmetric square wave. Unsymmetric digital signals haven't been found to have much more even harmonic content than odd harmonit content when viewed on a spectrum analyzer...until the digital signal pulse width is VERY short compared to its repetition time. The SRD is able to get about as short as such pulses go and the duty cycle is in fractions of a percent. [also "avalanche diode" which I'm sure that someone will bring up sooner or later to start another argument...:-) ] The original question was about "practical multiplier stages." Those would range from doublers to quintuplers. Going much higher HAS been done but it takes VERY expensive lab instruments to prove them out, such as with an SRD "comb generator." Comb generators have all sorts of harmonics but trying to extract, say, the 21st without passing the 20th or 22nd harmonic requires a very fussy high-Q filter. Some of the things _possible_ are not quite in the homebrewer workshop category...or they take a LOT of time to complete. I mentioned the passive diode doubler for the simple reason it IS simple when used with a distorted sinewave source (not a square wave). The effect of the two diodes in a "full-wave rectifier like" circuit creates an artificial 2nd harmonic by adding one sinusoid swing with the other, opposite-polarity sinusoid swing inverted by transformer action. Jim Pennell commented on that previously (and quite correctly). That makes for a broadband, non-fussy doubler circuit. Old thing and not a super whiz-bang state-of-the- art, hot-off-the-drawing-board wonder but it works. :-) Len Anderson retired (from regular hours) electronic engineer person |
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