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On the datasheet for CD4007 there are schematics for the input protection network:

CD4007 input protection network

and the output protection network:

CD4007 output protection network

On both, there are 2 diodes connected by a dashed line (D2 on the input and D1 on the output).

What does the dashed line mean?

Alex Malcoci
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1 Answers1

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The dashed line means that the diode is actually distributed across the resistor structure. The resistor is made using a doped region in the silicon, and there is an inherent PN junction between this doped region and the underlying silicon that contains it. So there is really just one diode, not two, but it is neither before nor after the resistor...it is part of the physical resistor structure itself.

Elliot Alderson
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  • Does it have any special properties compared to putting the resistor and the diode in series, or is the schematic just being specific as to the implementation of that resistor/diode structure? – Alex Malcoci Jan 01 '20 at 16:42
  • I don't know much about the properties of these distributed diodes, but if the diode and resistor were separate devices, and the diode was after the resistor, then it would be more straightforward to see how the resistor would limit the current through the diode. – Elliot Alderson Jan 01 '20 at 17:59
  • Thank you. Do you know the official name of such a structure? I cannot find much about it with any permutation of _diode_, _resistor_ and _distributed_. – Alex Malcoci Jan 01 '20 at 23:42
  • Schrödinger's diode :-) – Russell McMahon Jan 01 '20 at 23:52
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    @AlexMalcoci Try searching for "diffused resistor". The resistors were originally created by diffusing dopants into the silicon. These days they would be created via ion implantation, so I suppose you could also try "implanted resistor". – Elliot Alderson Jan 02 '20 at 01:01
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    @RussellMcMahon it turns into transistor when you decap the chip – Maple Jan 02 '20 at 05:30
  • @Maple: got any photos or links or other sources? :) – quetzalcoatl Jan 02 '20 at 13:00
  • @AlexMalcoci It's just a very simple structure that happens to get the job done. Separate diodes and resistor would be more complicated. – John Doty Jan 02 '20 at 22:13