Measuring waveform of small current pulse

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Hi Group,

I am looking for a way to measure the waveform of a current pulse, on
the other of 1-10uA, and with a rise time of ~1us, without disturbing
the 0.5V DC signal that is forced on this node. I was told this is
possible with a combination of Tektronix TM502A (power module
mainframe), AM503B (current probe amplifier module with digital scale
readout), and an oscilloscope. I was wondering if anyone here has
experience with such measurements using this set up, or may suggest a
better method. From reading the AM503B manual I get the impression that

it does not have uA resolution, but then I could have missed something.



Many thanks.


Dan

 

[Dave]

You can always run multiple loops through the current probe to gain the
signal.

 

[vasile]

Hi Group,

I am looking for a way to measure the waveform of a current pulse, on
the other of 1-10uA, and with a rise time of ~1us, without disturbing
the 0.5V DC signal that is forced on this node. I was told this is
possible with a combination of Tektronix TM502A (power module
mainframe), AM503B (current probe amplifier module with digital scale
readout), and an oscilloscope. I was wondering if anyone here has
experience with such measurements using this set up, or may suggest a
better method. From reading the AM503B manual I get the impression that

it does not have uA resolution, but then I could have missed something.

I don't know your tools parameters but this is quite easy with an
appropiate curent to voltage converter. 1uA...10uA and 1uS rise time is
not a special wave form.
A common voltage to current converter using a fast OA will do it.

greetings,
Vasile

 

[Winfield Hill]

was "Measuring waveform of small current pulse"

Dave answered...

You can always run multiple loops through the current probe to
gain the signal.

Just to answer wrt a AM503A, with a standard probe its most
sensitive setting is 1mA/div. The scope input is set to its
10mV/div setting, and with a 50-ohm termination. With these
settings, and with the 5MHz BW limit, my measured noise was
just a bit larger than the scope trace. With the scope gain
changed to 1mV/div = 100uA/div, the noise was about 1div, or
100uA p-p. Filtering the signal at 10kHz dropped the noise to
0.4mV or about 40uA p-p and the scope reported 13uA rms noise.

There was also a fairly large amount of dc drift, which means
such measurements are most easily made with ac coupling.

As Dave says, you can run multiple loops through the probe
to obtain a proportional improvement, perhaps up to 10x max.
If your pulse is repetitive, you can further improve the SNR
by putting your scope into averaging mode. Using all these
tricks, a 1uA pulse measurement might barely be possible.

BTW, a second probe I tried was noisier. YMWV.

 

[joseph2k]

Hi Group,

I am looking for a way to measure the waveform of a current pulse, on
the other of 1-10uA, and with a rise time of ~1us, without disturbing
the 0.5V DC signal that is forced on this node. I was told this is
possible with a combination of Tektronix TM502A (power module
mainframe), AM503B (current probe amplifier module with digital scale
readout), and an oscilloscope. I was wondering if anyone here has
experience with such measurements using this set up, or may suggest a
better method. From reading the AM503B manual I get the impression that

it does not have uA resolution, but then I could have missed something.



Many thanks.


Dan

The resolution is probe dependant, the ACP312 is the most sensitive, they
are all more than fast enough.

Try: www.tek.com/site/ps/0,,60-16458-INTRO_EN,00.html