This is about a very specific RF system on a chip -- NXP's SA636, "Low voltage, high-performance mixer FM/IF system...". Datasheet is here: https://www.nxp.com/docs/en/data-sheet/SA636.pdf. The datasheets and application notes differ in what looks like a critical way to me, and I'm wondering what route to take before I spend cash on PCBs.
I'm trying to build a radio for 162MHz, a frequency that should be well within limits for this IC. I'm injecting my local oscillator (LO) signal, but where, exactly, I do that isn't clear. The chip has four relevant pins, two for the RF input and two for the LO; the RF and LO signals are internally mixed via a Gilbert cell. On the LO side, the two pins look like this, with one pin connected to the base of an internal transistor and the other to its emitter:
But in the application notes, the LO is injected on the emitter side of that transistor: (note that the application notes are using the SSOP package, with different pin numbers compared to the HVQFN package. Pin 3 & 4 in SSOP == pin 1 & 2 in HVQFN, respectively)
So, I'm wondering where to connect my 151.3MHz LO -- should I connect to the base or to the emitter? My guess is the emitter, but that's going by feel and I'd like to think things through rather than just go with my gut.