Maker Pro
Maker Pro

Techniques for creating a 1GHz signal

M

mook johnson

Jan 1, 1970
0
Gents,

I may have toe venture from my cozy home in the sum 10MHz range to the
high frequency RF stuff on the hundreds of MHz to low GHz range.

First order of business is a 1GHz signwave generator.

What are the common techniques for generating something that high?

DDS? Hartley type oscillator, Crystal with upper harmonic filter to
isolate the 1GHz band. I'm thinking this will be the input to some
buffer so the output can hump some power. ~1W range into 50 ohms.

No detailed specs at this point just trying to get a head start on some
common techniques before the project kicks off.
 
M

mook johnson

Jan 1, 1970
0
Gents,

I may have toe venture from my cozy home in the sum 10MHz range to the
high frequency RF stuff on the hundreds of MHz to low GHz range.

First order of business is a 1GHz signwave generator.

What are the common techniques for generating something that high?

DDS? Hartley type oscillator, Crystal with upper harmonic filter to
isolate the 1GHz band. I'm thinking this will be the input to some
buffer so the output can hump some power. ~1W range into 50 ohms.

No detailed specs at this point just trying to get a head start on some
common techniques before the project kicks off.

I forgot to mention that this needs to be a circuit on a PCBA not a
piece of test equipment.
 
J

Jamie

Jan 1, 1970
0
mook said:
I forgot to mention that this needs to be a circuit on a PCBA not a
piece of test equipment.

Have you looked at Gilbert cells into a high pass filter.


Jamie
 
N

Nico Coesel

Jan 1, 1970
0
mook johnson said:
Gents,

I may have toe venture from my cozy home in the sum 10MHz range to the
high frequency RF stuff on the hundreds of MHz to low GHz range.

First order of business is a 1GHz signwave generator.

What are the common techniques for generating something that high?

A very easy way is an Analog devices ADF4350 and a filter. Not cheap
though...
 
If quantities are not huge, buy a VCO from MiniCircuits or Zcomm or Macom.. They
are available from octave-range (varicap tuned) to narrowband (coaxial
resonator.) Gain it up with cheap MMICs.

If you want to roll your own, get Randy Rhea's book

http://www.amazon.com/Oscillator-Design-Computer-Simulation-Randall/d...

GHz oscillator design is non-obvious.

There are some fast DDS chips around now, too.

maybe something like this:
http://www.analog.com/en/rfif-components/rfif-transceivers/adf7012/products/product.html


-Lasse
 
T

Tim Williams

Jan 1, 1970
0
John Larkin said:
GHz oscillator design is non-obvious.

Does that mean GHz amplifier design is obvious?

At most frequencies, amplifiers oscillate and oscillators merely amplify!

Tim
 
T

Tim Williams

Jan 1, 1970
0
Just to play?

First of all, do you have the equipment to see what you're doing? A scope
with 1GHz bandwidth is an obvious starting point; if you hope to see any
harmonics, 5G, 10G or more would be handy. Big $$$, but the most
familiar relative to time-domain slow stuff.

Specturm analyzer is much cheaper, even out past 10G or so, but doesn't
show time domain activity as well. To do that, you need to infer things
from sample period (e.g., 60Hz ripple modulating an amplifier, causing
amplitude modulation, only noticeable at certain refresh rates), sidebands
and so on. Everything's sideways-upside-down in the frequency domain.
But it's quite helpful for radio-ey things, where sidebands and harmonics
are important and easy to pick out.

You can plod along with, say, an RF voltage probe, but you don't know
anything about what's happening, just that it's there or not.

Second, you need parts to do it. MMICs are one thing. BJTs come in that
range, as do [Si] JFETs, MOS and the fancier PHEMTs and stuff. Offhand, I
don't have any stuff that goes that high, other than parts I've salvaged
that I can't find full datasheets for, if anything at all. Some good
starting points are BFQxxx's and such, many of which have been mentioned
here before; others can volunteer their favorite HF jellybeans.

Finally, you need the understanding. Have you played with radio style
circuits before, and got a grasp of impedance matching and transformation
and inductors and capacitors and filter design and...? It's easy to see
the analogy between an inductor and a thin trace, and a capacitor and a
thick trace; it's only another step to build a GHz oscillator with 1/4
wave stubs, or a filter with various segments stacked up. Of course, it's
another to design one from first principles and have it work correctly
(desired frequency, bandwidth and ripple, etc.), and it would be a whole
thing further to actually build one from copper clad with an X-Acto blade!
But as with lumped filters, there are design tools for that (ranging from
simple calculators to free programs to kilobuck design suites). So if you
already have a feeling for this sort of stuff, go for it. If you don't,
you might plan some more projects in the VHF range, where inductors and
capacitors are still reasonably inductive and capacitive, respectively,
keeping in mind your experience is directly applicable.

Some projects are pretty simple, too, even with whatever considerations.
A pulsed oscillator and wideband detector can be used for very crude
radar, and it doesn't really even matter what frequency the oscillator
runs at. If it's making an RF signal, you can be reasonably assured it's
doing it at whatever GHz your stubs and stuff are tuned for. Zap it off
an antenna and watch the return blip. Stuff like this was done back in
the days when scopes were barely pushing 10MHz, and GHz was generated with
freaky vacuum tubes, like klystrons, backward-wave oscillators and
magnetrons.

Tim
 
Gents,

I may have toe venture from my cozy home in the sum 10MHz range to the
high frequency RF stuff on the hundreds of MHz to low GHz range.

First order of business is a 1GHz signwave generator.

Stability requirements ? Free running or locked to some reference ?

Tuning range ?

What are the common techniques for generating something that high?

In the old days for a narrow frequency range a string of 2x and 3x
multiplier stages with a resonator between each stage. For a larger
tuning range push pull frequency doublers, which did not need much
filtering between stages.

These days apparently the simplest would be use a VCO in some PLL
construction. Fixed or variable modulus dividers are available to
several GHz. Alternatively, use some mixer system to reduce the VCO
frequency to some lower frequency and use some low frequency divider
or lock the difference frequency to some lower frequency variable
signal source.

Of course, one must be careful with topology and loop filter design,
in order to keep the phase noise at acceptable levels.

The problem with ordinary DDS design is that you would need to clock
it above 3 GHz to generate 1 GHz. This would consume a lot of power
and most likely would be quite expensive. There are some alternative
ideas of using a VCO at 1 GHz feeding the _clock_ input of the DDS and
program the chip to produce 1 MHz and compare this to a 1 MHz crystal
and use the feedback to control the VCO so that the DDS produces 1
MHz.
DDS? Hartley type oscillator, Crystal with upper harmonic filter to
isolate the 1GHz band.

Sounds like some wave analyzers used decades ago. Those used some
signal sources that produced a lot of harmonics (such as a step
recovery diode), mix it down with a VFO to some low crystal filter
frequency (say 10 MHz) and then mix the filtered signal back to
original frequency using the same VFO, thus the VFO drift was
canceled. By tuning the VFO, you could select which harmonic you
needed.
 
O

Owen Roberts

Jan 1, 1970
0
50-2000 Mhz is fairly easy with stock VCOs and TI, Fujitsu or AD
PLLs.

AD products often come with the VCO on Chip.

Depending on what your doing, the most important beginner's tools
for learning basic PLL are probablty:
1. A decent frequency counter.
2. RF power meter, Even the low cost ones.
3. Spec-An.
4. Oscilloscope of course, for the loop filter.
5. Older PLL appnotes such as MC145151, MC145170 etc where they give
good, simple, examples.

I'm going to disagree with Tim on the scope bandwidth, for many
applications 10 or 100 Mhz is fine.

The rationale being the VCO power level at the prescaler is usually
a common problem at the design stage. A frequency counter is
inexpensive and shows lock and programming errors quickly. The Spec
An is there for the harmonics and RF levels.

Learning to make microstrip with free tools like APPCAD, and adding
gain with MMICs helps.

I like the TI PLLatinum parts for the fact they often bring the
prescaler count out on a pin.

LMX2430 for example.

Motorola's AN535 is widely available on the net.

Just a few ideas,

Steve
 
N

Nico Coesel

Jan 1, 1970
0
Jan Panteltje said:
If you can spend the 10 dollars or so:
http://www.ebay.com/itm/Sirenza-VCO...431?pt=LH_DefaultDomain_0&hash=item25591b800f
There is a wide choice of frequencies and manufacturers on ebay for that kind of stiff.

But you still need a PLL and other circuitry. The ADF4350 just needs a
reference clock, a few passive parts and a small controller to set the
registers and it produces about any frequency between 135MHz and
4.4GHz. There is an improved version as well which goes as low as
(IIRC) 38MHz.
 
O

Owen Roberts

Jan 1, 1970
0
I did get two samples of those. Wonderful part. Very tiny package.

Steve
 
M

Mark

Jan 1, 1970
0
Specturm analyzer is much cheaper, even out past 10G or so, but doesn't
show time domain activity as well.  To do that, you need to infer things
from sample period (e.g., 60Hz ripple modulating an amplifier, causing
amplitude modulation, only noticeable at certain refresh rates), sidebands
and so on.  Everything's sideways-upside-down in the frequency domain. here or not.

Tom, I have three words of advice that may help you....

"ZERO SPAN MODE"

Mark
 
Top