Electronics > Beginners
Voltage Drop at Breadboard
tggzzz:
--- Quote from: bd139 on March 19, 2019, 10:50:38 pm ---A point to bear in mind when using or not using breadboards: Sometimes signal integrity and layout doesn't actually matter that much!
I'm doing some sub 1KHz stuff with opamps at the moment which requires a lot of trial and error. I'm doing it on a 3M breadboard and am giving zero fucks :)
--- End quote ---
Yup.
A 1kHz analogue signal isn't going to have much energy above 100MHz. A 1kHz digital signal would, though.
The other issues with analogue circuits are that that although your signal may only be 1kHz, it is quite possible for the circuit elements to have much higher frequency response. Remember the old adage: "amplifiers oscillate, oscillators don't" :)
tggzzz:
--- Quote from: rdl on March 19, 2019, 10:37:33 pm ---I was not sure what more information another 6 inches of wire would add, after all, there is already ~425mm of conductor including 8 wire to board insertions, but I looked at it anyway.
I don't actually see much difference.
While I was at it, I measured the resistance of one 425mm length of breadboard rails (plus wire jumpers) at 18 ohms. If I did the math right, this agrees closely with the 40 mV voltage drop I recorded previously. The capacitance across the pair of rails (all 425mm) was measured as about 85 pF.
--- End quote ---
That's still a well-controlled slow risetime, unlike that seen with jellybean logic. Even with that signal, you can see some oscillation at ~100MHz.
I don't know how 100MHz compares with your scope's bandwidth, but a 100MHz signal on a 100MHz scope+probe would be 3dB down, i.e. only 70% of the actual amplitude.
bd139:
--- Quote from: tggzzz on March 20, 2019, 09:38:33 am ---
--- Quote from: bd139 on March 19, 2019, 10:50:38 pm ---A point to bear in mind when using or not using breadboards: Sometimes signal integrity and layout doesn't actually matter that much!
I'm doing some sub 1KHz stuff with opamps at the moment which requires a lot of trial and error. I'm doing it on a 3M breadboard and am giving zero fucks :)
--- End quote ---
Yup.
A 1kHz analogue signal isn't going to have much energy above 100MHz. A 1kHz digital signal would, though.
The other issues with analogue circuits are that that although your signal may only be 1kHz, it is quite possible for the circuit elements to have much higher frequency response. Remember the old adage: "amplifiers oscillate, oscillators don't" :)
--- End quote ---
Indeed.
I've seen a 2n3904 oscillating well into VHF (190MHz) on a breadboard. I assume it was due to the breadboard stray capacitance and collector wire inductance acting as a colpitts style oscillator. I played with it for a bit to see if I could tune it then gave up and shut it up by leveraging the miller effect with a 47pF across collector/base. I was establishing DC operating point of a circuit before I moved it in situ on a manhattan construction board.
tggzzz:
Quote from: rdl on Today at 12:55:08 am
One more thing, and this is something that I've previously seen evidence of potentially being a real problem. This image is where the crosstalk is looked at on the long 425mm path. The blue trace is the actual signal on the "positive" rail (red jumpers), and the yellow is the induced signal on the "negative" (black jumpers) rail.
Here the same signal is running through one of the five hole vertical strips (blue trace) with the crosstalk that appears on the adjacent five hole socket strip (yellow trace). Doesn't look that bad actually.
I'd like to point out to anyone reading this thread that running a 10MHz signal through 425mm of conductor, including multiple wire to board insertion connections, is somewhere beyond "worst case scenario". I'm sure decent quality breadboards have a limit to their usefulness, but I don't know where it is and I'm not inclined to go looking today.
--- End quote ---
I'm not entirely sure what you are showing there, since the detailed wiring matters.
However, NEXT and FEXT on signals can be serious problems. (NEXT= near end crosstalk, FEXT= far end crosstalk). But I doubt the traces show those.
More important is ground bounce, which does cause serious problems even on well-laid out multilayer PCBs. It is one of the reasons that modern busses tend to be serial rather than the old-time parallel busses.
Do the calculation using, say, a 3V signal swing with a 10pF load capacitance and a 2ns transition time, and a 6inch/150nH wire:
* current ic required to charge a capacitor C through a voltage dV in time dt is ic= C dV/dt, so ic = 15mA
* voltage Vi induced across a capacitor by a changing current dI in time dt is Vi = L dI/dt, so Vi = 1.125V
* and you can multiply that by however many outputs are changing simultaneously!Obviously you can play around with the precise numbers until the cows come home, but having a +-1V signal "suddenly" appear on the ground/Vcc line isn't going to lead to operation within the IC's specification.
rdl:
--- Quote from: tggzzz on March 20, 2019, 10:09:09 am ---I'm not entirely sure what you are showing there, since the detailed wiring matters.
--- End quote ---
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version