I want to reproduce an LFO circuit where the author uses NE5517N OTA. So I started form looking for the LTSpice model of NE5517. Unfortunately with no success, I decided to make NE5517 simulation and use it as subcircuit. But getting into the schematics downloaded from On Semiconductor web, I have faced some questions that are "legended" on this picture: NE5517 Schematics

  1. What type of transistor is this (with 2 collectors going out of it)?
  2. What value is this R1 of could be?
  3. Where can I find the params of PNPs used in schematic.
  4. Where can I find the params of NPNs used in schematic.

Please help!

  • 1
    \$\begingroup\$ Unless you need a rather precise modeling, the LM13700 is spec'ed almost identically, so you could use an LM13700 model instead. Those are readily found on-line. \$\endgroup\$ – Timo Nov 2 '16 at 9:54

1) That is actually a PNP current mirror. On a chip you can, instead of drawing 2 PNPs, draw one larger one but split the collector. Just replace this 2-collector PNP with 2 normal PNPs in a mirror configuration.

2) The value is anyone's guess, it determines the value of the biasing current through Q15 and Q16. 10 mA would be a reasonable assumption so then R1 would be 0.7 V / 10 mA = 70 ohms

3 + 4) The actual sizes of the transistors is the manufacturer's secret unless you would decap an NE5517 and measure it under a microscope. But don't worry about the parameters as they do not really matter that much.

Are you aware that all the diodes are actually also NPNs and PNPs with base and collector shorted ? Where connected in parallel with an NPN it will be an NPN and the same for PNP. Like Q8 and D5, that's actually a current mirror !

The only diodes that are not the input of a current mirror are D2, D3 and D7.

  • \$\begingroup\$ Your answer on 3+4... Do I have to replace all these diodes with NPNs and PNPs or using 1n914 model is ok? \$\endgroup\$ – Roman Nov 1 '16 at 20:37
  • \$\begingroup\$ An 1n914 is a diode. The only real diodes in the circuit are D2, D3 and D7. So there you could use the 1n914. But I would forget about that 1n419. I would use an "NPN diode" (short the base and the collector) for all diodes. Except D4 and D6, these need to be PNP diodes. If you have trouble comprehending why this is, I suggest that you read a book about analog IC design. \$\endgroup\$ – Bimpelrekkie Nov 1 '16 at 20:43
  • \$\begingroup\$ using the LTSpice 2N3906 and 2N3904 will work? \$\endgroup\$ – Roman Nov 1 '16 at 20:51
  • \$\begingroup\$ I have no idea as I have not tried that. So go ahead and try it. If you're lucky it will work. But if not you will have a hard time getting this to work with your level of experience. \$\endgroup\$ – Bimpelrekkie Nov 1 '16 at 20:54
  • \$\begingroup\$ Why not simply use an ideal voltage controlled current source instead of this NE5517 ? \$\endgroup\$ – Bimpelrekkie Nov 1 '16 at 20:55

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