EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: asw6 on May 29, 2024, 05:45:21 pm
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Hi everybody,
I recently came across this wire (see picture) that has been soldered at one end, and running parallel over a couple of resistors. What is its purpose? I assume EMF suppression, would appreciate some pointers to any information on the subject. The circuit in question is a low noise Transimpedance Amplifier, and the resistors are found on the signal input.
Thanks!
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That does seem wrong. If that would be high frequency RF circuit, then you could maybe think that it's some weird tuning thingy, filter element, stub. But it's not a RF circuit. It could be frequency response compensation, but I really doubt that, I think that any manufaturer with at least some self respect would never implement it like that. The loose end also is not isolated and it has a hook. Like it was supposed to be soldered to something, but was forgotten? I have no idea. Perhaps reverse engineering could give an answer. Maybe you could find photos online how other devices look inside?
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I have several units, and they have all been wired the same way. I notice the end with the hook appears to have been intentionally left bare of insulation, that’s now leads me to think it might be some sort of make shift switch for testing? I will have a go at reverse engineering the circuit. The part is an Analogue Module 341-2-N which appears to be based around an OP27 op-amp.
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It does look, that a couple of bumps during transportation could short that loose end to the nearby node. Even if the chance is very small, it is puzzling why anyone would leave it like that.
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Most likely a gimmick capacitor. Compare capacitance of the wire to the nearby resistors, versus their value, and the resulting time constant or break frequency with respect to the amplifier bandwidth. TIAs often operate on low capacitance sources, with high impedance otherwise, and very high gain, hence the high value resistors (that's what, 100M there?), and sensitivity to mere fractional pF in the feedback network.
Tim
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It is a gimmick capacitor made to compensate the frequency response of the high value resistor. Schematics sometimes show a line parallel to the resistor and connected to one end. Oscilloscope probes may do the same thing for their high value input series resistor or use transmission line construction.
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Now there's a term I havent heard for while. Neutralise those damn tubes!