"Paul Burridge" wrote in message
news
On Sun, 11 Apr 2004 14:14:56 +0200, "Fred Bartoli"
r_AndThisToo wrote:

Don't let Paul dream too much about picoseconds.

Well, quite. I wouldn't know what to do with all those extra
harmonics, anyway. :-)
Diodes sound great, but I'm heavily put off by that comment earlier in
the thread that they're prone to self oscillation. :-( What's a
"parametric device" anyway?

Parametric operation is when you have a parameter such as diode capacitance
that varies with voltage. The non-linearity of the parameter makes it act as
a multiplier, mixer or an amplifier. Parametric amplifiers (they need to be
'pumped' with an oscilllator) used to be very popular for microwave use. If
you have inadvertently make yourself a parametric amplifier with your diode
it could oscillate given the right conditions and do all sorts of strange
things. In your hands, this is a strong possibility. 8-)

Leon

If I understand correctly, you're interested in harmonics up in the
70MHz region. To me it seems silly to use diodes capable of
generating a comb of harmonics out to 20GHz for that. An advantage--a
big advantage--of the tiny logic is that you get considerable power
gain in the stage, and the sot-23 package is likely no larger than the
diode you might have used anyway. The edges, as others have pointed
out, are PLENTY fast enough for what I believe you want to do.

Whether you use diodes or gates, your size problem will be the
harmonic-selection filter. As you've learned (and I trust not
forgotten already), you need either multiple poles in your filter or a
rather high Q. You _could_ get the high Q with crystals, but of
course then you're locked down to particular frequencies. For high
multiplication factors to low-VHF frequencies, it's probably hard to
beat a PLL for (potentially) small size.

In offering suggestions, it would also be helpful to us to know your
actual needs for signal purity, both close-in (phase noise) and
broadband (other harmonics, etc.)

If you do use diodes for higher-order harmonic generation, and not
just a simple full-wave-rectifier type frequency doubler, I suppose
you want something of the nature of a step recovery diode. That
implies minority carrier stored charge in the diode, and that would
preclude using a Schottky diode (which would work great in the
full-wave-rectifier type doubler). If you get into actually wanting
to generate harmonic combs out to microwave frequencies, it's probably
worthwhile looking for diodes actually characterized for step recovery
service. But I really think that's way beyond what you are trying to
accomplish right now.

Cheers,
Tom


Paul Burridge wrote in message . ..
On Sun, 11 Apr 2004 14:14:56 +0200, "Fred Bartoli"
r_AndThisToo wrote:

Don't let Paul dream too much about picoseconds.

Well, quite. I wouldn't know what to do with all those extra
harmonics, anyway. :-)
Diodes sound great, but I'm heavily put off by that comment earlier in
the thread that they're prone to self oscillation. :-( What's a
"parametric device" anyway?

In order to achieve results that good, one have to pay very careful
attention to "wiring". There's still a lot of room for Paul to improve his
PCB design skills ;-)

Fair comment. But I *am* working on it!

If you do use diodes for higher-order harmonic generation, and not
just a simple full-wave-rectifier type frequency doubler, I suppose
you want something of the nature of a step recovery diode. That
implies minority carrier stored charge in the diode, and that would
preclude using a Schottky diode (which would work great in the
full-wave-rectifier type doubler). If you get into actually wanting
to generate harmonic combs out to microwave frequencies, it's probably
worthwhile looking for diodes actually characterized for step recovery
service. But I really think that's way beyond what you are trying to
accomplish right now.

My turn to learn something here. Tom, would you elaborate a bit on the above
please? I know SRD's are comb generators out to visible light, but they're
also 50 percent hard to find and 50 percent magic. I've been using
Schottky's for X16 multipliers to 2 GHz, am I doing something wrong? (I keep
promising myself that I'm gonna substitute an MMIC for that one day, I DID
find the "Filter Gain" in the line length from generator to filter), THAT
was both impressive AND helpful. If I go with the MMIC, any preference of
Silicon over GaAs?

Regards

W4ZCB

If you do use diodes for higher-order harmonic generation, and not
just a simple full-wave-rectifier type frequency doubler, I suppose
you want something of the nature of a step recovery diode. That
implies minority carrier stored charge in the diode, and that would
preclude using a Schottky diode (which would work great in the
full-wave-rectifier type doubler). If you get into actually wanting
to generate harmonic combs out to microwave frequencies, it's probably
worthwhile looking for diodes actually characterized for step recovery
service. But I really think that's way beyond what you are trying to
accomplish right now.

My turn to learn something here. Tom, would you elaborate a bit on the above
please? I know SRD's are comb generators out to visible light, but they're
also 50 percent hard to find and 50 percent magic. I've been using
Schottky's for X16 multipliers to 2 GHz, am I doing something wrong? (I keep
promising myself that I'm gonna substitute an MMIC for that one day, I DID
find the "Filter Gain" in the line length from generator to filter), THAT
was both impressive AND helpful. If I go with the MMIC, any preference of
Silicon over GaAs?

Regards

W4ZCB

If I understand correctly, you're interested in harmonics up in the
70MHz region. To me it seems silly to use diodes capable of
generating a comb of harmonics out to 20GHz for that. An advantage--a
big advantage--of the tiny logic is that you get considerable power
gain in the stage, and the sot-23 package is likely no larger than the
diode you might have used anyway. The edges, as others have pointed
out, are PLENTY fast enough for what I believe you want to do.

Whether you use diodes or gates, your size problem will be the
harmonic-selection filter. As you've learned (and I trust not
forgotten already), you need either multiple poles in your filter or a
rather high Q. You _could_ get the high Q with crystals, but of
course then you're locked down to particular frequencies. For high
multiplication factors to low-VHF frequencies, it's probably hard to
beat a PLL for (potentially) small size.

In offering suggestions, it would also be helpful to us to know your
actual needs for signal purity, both close-in (phase noise) and
broadband (other harmonics, etc.)

If you do use diodes for higher-order harmonic generation, and not
just a simple full-wave-rectifier type frequency doubler, I suppose
you want something of the nature of a step recovery diode. That
implies minority carrier stored charge in the diode, and that would
preclude using a Schottky diode (which would work great in the
full-wave-rectifier type doubler). If you get into actually wanting
to generate harmonic combs out to microwave frequencies, it's probably
worthwhile looking for diodes actually characterized for step recovery
service. But I really think that's way beyond what you are trying to
accomplish right now.

Cheers,
Tom


Paul Burridge wrote in message . ..
On Sun, 11 Apr 2004 14:14:56 +0200, "Fred Bartoli"
r_AndThisToo wrote:

Don't let Paul dream too much about picoseconds.

Well, quite. I wouldn't know what to do with all those extra
harmonics, anyway. :-)
Diodes sound great, but I'm heavily put off by that comment earlier in
the thread that they're prone to self oscillation. :-( What's a
"parametric device" anyway?

In order to achieve results that good, one have to pay very careful
attention to "wiring". There's still a lot of room for Paul to improve his
PCB design skills ;-)

Fair comment. But I *am* working on it!

On Sun, 11 Apr 2004 14:14:56 +0200, "Fred Bartoli"
r_AndThisToo wrote:

Don't let Paul dream too much about picoseconds.

Well, quite. I wouldn't know what to do with all those extra
harmonics, anyway. :-)
Diodes sound great, but I'm heavily put off by that comment earlier in
the thread that they're prone to self oscillation. :-( What's a
"parametric device" anyway?

In order to achieve results that good, one have to pay very careful
attention to "wiring". There's still a lot of room for Paul to improve his
PCB design skills ;-)

Fair comment. But I *am* working on it!

"Robert Baer" a écrit dans le message news:
...
Paul Burridge wrote:

On Sat, 10 Apr 2004 08:22:21 GMT, Robert Baer
wrote:

Not a varactor (diode), but a switching diode; fast. Snap-off is lotz
better.
And they are a *LOT* smaller!

Thanks, Robert (and all else)
I'd prefer a diode solution as there'd be no power supply requirements
for each device. The tiny size is an added bonus, of course. But
what's the drawback with superfast switching diodes as against active
inverters? I'm sure there must be (at least) one...

An active inverter is S L O W by comparison; a good, fast diode can
have turnoff times in the tens of picoseconds region.


Don't let Paul dream too much about picoseconds.
In order to achieve results that good, one have to pay very careful
attention to "wiring". There's still a lot of room for Paul to improve his
PCB design skills ;-)

Thanks,
Fred.

Paul Burridge wrote:

On Sat, 10 Apr 2004 08:22:21 GMT, Robert Baer
wrote:

Not a varactor (diode), but a switching diode; fast. Snap-off is lotz
better.
And they are a *LOT* smaller!

Thanks, Robert (and all else)
I'd prefer a diode solution as there'd be no power supply requirements
for each device. The tiny size is an added bonus, of course. But
what's the drawback with superfast switching diodes as against active
inverters? I'm sure there must be (at least) one...

An active inverter is S L O W by comparison; a good, fast diode can
have turnoff times in the tens of picoseconds region.