I am interfacing 1.8V and 3.3V UART lines, and due to one of the module's UART lines being a boot-config pin, it cannot be pulled up during the boot process. The module manufacture recommends the transistor circuit below for the logic level shifting.

I actually tried routing these lines through a 1.8 to 3.3V logic level shifter IC I already had on my PCB. It is the second picture below, but with that set-up I had to cut the traces on the boot-config line just to get the module to boot properly.

But my question is with this transistor circuit, I wasn't given any other information but am assuming these are NPN transistors. Is this correct, and are there any other major considerations I should take into account when laying out the pcb?

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1 Answer 1


The transistors in those reference circuits are all NPN - the emitter arrows are Not Pointing iN.

On an PNP transistor, the emitter arrows are Pointing iN Proudly.

(and MOSFETs have totally different symbols)

  • \$\begingroup\$ Do you know what the NM over the capacitors is? \$\endgroup\$
    – Feynman137
    Jan 2, 2022 at 0:59
  • \$\begingroup\$ Probably "Not Mounted". If making a PC board, place a footprint for them in case we need them. \$\endgroup\$ Jan 2, 2022 at 1:12

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