Winfield Hill said:
Frank Mikkelsen wrote...
What are you working on? Is it a sinusoidal output whose
frequency you scan, or some other kind of waveform? How
precise must the output be?
I am working on a sweep generator to exercise an ion trap, used on a atom
physics experiments on cern
(
http://public.web.cern.ch/Public/Welcome.html). The ion trap consists of
6 electrodes each having a capacity to ground of 300 pf. The design of the
ion trap can't be changed and it is placed in a vacuum chamber and the
temperature must be close to 0 Kelvin -> no power dissipation allowed in
the chamber. The signal paths to each electrode are precisely matched. The
generator consist of six outputs producing the same frequencies to each
electrodes with a constant phase offset during the frequency sweep, I need
therefore a close phase match f(frq) for each output stages, and therefore
I attempt have as smoothly phase change as possible up to 30 MHz.
The frequencies with constant phase offset during the sweep are generated
with six synchronize AD9954.
The requirement to phase match between the electrodes over a 1MHz - 30 MHz
sweep are not defined but the scientist wished around 1 deg which I am not
sure I can meet.
Frank
BTW, you could still take advantage of output resonance,
peaking-coil style, by placing a parallel inductor with
a series R, making a resonance at the highest frequency,
that's low-Q, but still helpful in reducing the current
and shifting its phase. The Q-spoiling resistor becomes
a simple resistive load at low frequencies. A series cap
can be used to remove or reduce its effect at DC and the
lowest 1MHz frequency region.
Sounds challenging. I used to love that kind of work. A decade of nothing
but very mundane work ruined me.
