17
\$\begingroup\$

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?

\$\endgroup\$

1 Answer 1

Reset to default
19
\$\begingroup\$

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.

\$\endgroup\$
8
  • \$\begingroup\$ 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? \$\endgroup\$
    – Alex Malcoci
    Jan 1, 2020 at 16:42
  • \$\begingroup\$ 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. \$\endgroup\$
    – Elliot Alderson
    Jan 1, 2020 at 17:59
  • \$\begingroup\$ 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. \$\endgroup\$
    – Alex Malcoci
    Jan 1, 2020 at 23:42
  • 3
    \$\begingroup\$ @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". \$\endgroup\$
    – Elliot Alderson
    Jan 2, 2020 at 1:01
  • 1
    \$\begingroup\$ @RussellMcMahon it turns into transistor when you decap the chip \$\endgroup\$
    – Maple
    Jan 2, 2020 at 5:30

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.