Dear Peter,
I checked the article. It looks nice and simple, however on a second
look it shows a number of design flaws The claimed temperature
stability is more a sort of assumption: In the text (not the abstract)
it is stated as:
"The measured temp.sensitivity is about 1ps/K for small temperature
changes around the 23 degrees C average temperature."
The claim of the temp.sensitivity is more or less based on an
assumption. It is not defined how "big" a "small temperature change is".
From this vague assumption it is extrapolated that the sensitivity is 1
ps/K doesn't look like a scientific claim to me. This value is not
measured or verified by measurements, at least it is not presented in
the paper.
Furthermore the system uses standard non-paired 2N3904 transistors for
the comparator, and even worse, they are used at different bias-currents
which means different temperature coeefficients. So the switching point
WILL change with temperature... When using these transistors, they
should be used at fairly high collector-currents 40-50 mA for a fast and
"fairly" stable temperature response. The output stage is not optimized
for that, the collector-current, hence switching speed depend on the
circuits output load. Other design-flaws:
* The supply voltages for certain parts are stabilized bij 5.1 Volt
zeners.
* The schmitt-trigger used is not very stable for temperature
With other words, a nice design, when placed in a climate chamber. But
the claim for the temperature stability is way too high.
Jeroen PE1RGE
[EMAIL PROTECTED] wrote:
You might look at:
G. Brida
High resolution frequency stability measurement system
Review of Scientific Instruments, Vol. 73, no. 5, pp. 2171-2174,
2002.
This article reports on the frequency stability measurement system
based upon the dual-mixer time-difference scheme working at 10 MHz
with 1 Hx beat note. The principle of the system is reviewed, the
design approach is described, and the experimental results are
presented. The measurement system shows a stability of 5.6ยท10-14/t
(Allan deviation) and a temperature sensitivity of some picoseconds
per Kelvin. An approach to reduce crosstalk problems has been
tested.
Sorry,I don't have an electronic copy at the moment.It specifically
addresses the gain/bandwidth zerocrossing detector issues.
Peter ZL2AYX
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Ing. Jeroen Bastemeijer
Delft University of Technology
Department of Electrical Engineering
Electronic Instrumentation Laboratory
Mekelweg 4, Room 13.090
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The Netherlands
Phone: +31.15.27.86542
Fax: +31.15.27.85755
E-mail: [EMAIL PROTECTED]
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