If you need assistance, please send an email to forum at 4hv dot org. To ensure your email is not marked as spam, please include the phrase "4hv help" in the subject line. You can also find assistance via IRC, at irc.shadowworld.net, room #hvcomm.
Support 4hv.org!
Donate:
4hv.org is hosted on a dedicated server. Unfortunately, this server costs and we rely on the help of site members to keep 4hv.org running. Please consider donating. We will place your name on the thanks list and you'll be helping to keep 4hv.org alive and free for everyone. Members whose names appear in red bold have donated recently. Green bold denotes those who have recently donated to keep the server carbon neutral.
Special Thanks To:
Aaron Holmes
Aaron Wheeler
Adam Horden
Alan Scrimgeour
Andre
Andrew Haynes
Anonymous000
asabase
Austin Weil
barney
Barry
Bert Hickman
Bill Kukowski
Blitzorn
Brandon Paradelas
Bruce Bowling
BubeeMike
Byong Park
Cesiumsponge
Chris F.
Chris Hooper
Corey Worthington
Derek Woodroffe
Dalus
Dan Strother
Daniel Davis
Daniel Uhrenholt
datasheetarchive
Dave Billington
Dave Marshall
David F.
Dennis Rogers
drelectrix
Dr. John Gudenas
Dr. Spark
E.TexasTesla
eastvoltresearch
Eirik Taylor
Erik Dyakov
Erlend^SE
Finn Hammer
Firebug24k
GalliumMan
Gary Peterson
George Slade
GhostNull
Gordon Mcknight
Graham Armitage
Grant
GreySoul
Henry H
IamSmooth
In memory of Leo Powning
Jacob Cash
James Howells
James Pawson
Jeff Greenfield
Jeff Thomas
Jesse Frost
Jim Mitchell
jlr134
Joe Mastroianni
John Forcina
John Oberg
John Willcutt
Jon Newcomb
klugesmith
Leslie Wright
Lutz Hoffman
Mads Barnkob
Martin King
Mats Karlsson
Matt Gibson
Matthew Guidry
mbd
Michael D'Angelo
Mikkel
mileswaldron
mister_rf
Neil Foster
Nick de Smith
Nick Soroka
nicklenorp
Nik
Norman Stanley
Patrick Coleman
Paul Brodie
Paul Jordan
Paul Montgomery
Ped
Peter Krogen
Peter Terren
PhilGood
Richard Feldman
Robert Bush
Royce Bailey
Scott Fusare
Scott Newman
smiffy
Stella
Steven Busic
Steve Conner
Steve Jones
Steve Ward
Sulaiman
Thomas Coyle
Thomas A. Wallace
Thomas W
Timo
Torch
Ulf Jonsson
vasil
Vaxian
vladi mazzilli
wastehl
Weston
William Kim
William N.
William Stehl
Wesley Venis
The aforementioned have contributed financially to the continuing triumph of 4hv.org. They are deserving of my most heartfelt thanks.
Registered Member #9614
Joined: Mon Jan 14 2013, 10:00PM
Location:
Posts: 44
Trying to help a friend figure out how to measure the supply current of an SRAM chip. He'd like to see how much current the chip draws while writing a bit, which takes ~10nS.
Is a small resistor and a high bandwidth op amp the way to go?
Registered Member #53
Joined: Thu Feb 09 2006, 04:31AM
Location: Ontario, Canada
Posts: 638
Could you supply it from a source with a nice big capacitor and measure the current before that cap? It would take out all the ripple and leave you with the average current draw.
Registered Member #1792
Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527
Oscilloscope makers have grappled with this exact issue. Keysight has a new line of products they're calling "Device Current Waveform Analyzers" specifically for measuring small currents at high speeds.
Otherwise you'll need to go the more traditional route of a series resistor. There are some challenges to measure very small curents very quickly. In general you want a larger resistor the smaller your current is to increase the voltage signal, and you can also get away with that because the voltage drop to the chip will be low if the current is low. The preamp will need to have a low enough offset voltage relative to the signal you are measuring, suitable common mode range, and a small enough input capacitance to rise fast enough with the value of resistor you're using.
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
Two approaches spring to mind.
One is to use a series resistor and a high speed voltage gain amplifier. The other is to use a transimpedance amplifier. The difference between these is whether there is a significant or insignificant change in rail voltage respectively.
The choice starts by understanding whether the SRAM can tolerate a rail bounce and still work properly, which means not only store valid data, but also draw the current it normally draws. Although (say) 50mV should be plenty to read on a scoope and is well within its static rail tolerance, are there dynamic bias things going on inside an SRAM that mean that rail just has to be nailed still when it wants to draw write current? Those SRAM chips require rail decoupling for a reason.
One way to check this would be to measure the current with increasing values of resistor. Does the measurement show a systematic trend. At what resistance does the SRAM fail to write properly?
There are lots of app notes for the use of transimpedance amplifiers. I put 'high speed photodiode amplifier' into the usual search engine, and on the first page were pdfs for 1 1Mbit/s amp, Texas OPA380, and a 10Gbit/s amp MAX3970. OK, the second one is only available in dice, but you get the general conclusion that there's a wide range of devices out there. Add 'application note' to the search, and there's plenty of detailed help to get low noise and wide bandwidth out of the things.
This site is powered by e107, which is released under the GNU GPL License. All work on this site, except where otherwise noted, is licensed under a Creative Commons Attribution-ShareAlike 2.5 License. By submitting any information to this site, you agree that anything submitted will be so licensed. Please read our Disclaimer and Policies page for information on your rights and responsibilities regarding this site.