I have a circuit board, 4 layers, L2 being ground, 12 mils of FR4 between L1 and ground.
I was wondering what is the parasitic capacitance across R13.
So I found a bare board with a similar geometry.
I measured 0.05 pF between the pad pair in the center, 3T measurement.
Adding a 1Meg 0603 resistor, it went up to 0.085 pF.
(used my faithful pale green Boonton 72)
-- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
On a sunny day (Mon, 09 Dec 2013 21:37:04 -0800) it happened John Larkin wrote in :
Try again with a pink one.
Just for grins,try a 10Meg resistor..you may be in for a small surprise.
I've put the gear away, so it would be inconvenient. What do you think would happen?
-- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
I was half asleep; also use a 1pF and a 10pf capacitor (0603 natch). 10meg R should make little change, 1pF and 10F should add a small amount,theoretically (Cadd plus your 0.085pF) in parallel to "original"
0.085pF.
I'm doing a 3-terminal capacitance measurement between those pads, so any cap that I put in parallel with that resistor will add linearly to what I'm measuring. Pad-to-ground capacitance isn't as important in this circuit as pad-pad.
The Boonton is great. I ran coaxes out about 2 feet, and transitioned to homemade probes, hardline coax with a bit of center conductor poking out. Boonton ground is connected to the PCB ground plane. I almost touch the probes to the pair of pads, zero the Boonton, then touch down. The low range is 1 pF full scale.
-- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
Often true--in TIAs and bootstraps, for example.
And once it's zeroed, it sits there all afternoon reading 0.000 pF. (I have the digital version.)
Beautiful.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
I had a meter like that once. ;-)
Bless you. It's folks that surplus good kit that have made my lab what it is. ;)
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Errr... he might mean that the fuse was blown.
Does it have a mirror behind the digits?
-- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation
Of course. "I had a xxxx like that once" is an ancient gag line.
Cheers
Phil Hobbs
No, which is a good thing--otherwise I might fall in love with my reflection. ;)
Cheers
Phil Hobbs
Cool!
Whoosh... right over my head. Thanks.
Yeah, they're widely available on eBay for $100-$200. I have two 72BD digital ones and a 72A analogue one. Total price: $456 plus $67 shipping (three separate orders). Really great gizmos.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
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