New video: Basics of the Gilbert Cell - multiplier/mixer/modulator

[w2aew]

My latest video, by multiple requests, is a basic overview of the operation of a Gilbert Cell four quadrant analog multiplier, mixer, balanced modulator, etc.

[Tac Eht Xilef]

Thanks for these videos, Alan - as always, a nice clear and concise explantion of the subject. I often find myself referring to them as a refresher or referring others to them to save them from my mangled explanations

One thing that's never been particularly intuitive to me is the common use of the NE602 & friends as an RF->IF mixer, particularly when used as a switching downconverter/mixer (e.g. as typical in 10.7MHz/455kHz IF -> 12kHz soundcard SDR adaptors). There's something there that just doesn't stick with me, and I'm not quite sure what - maybe how it manages to convert without destroying the amplitude/phase information carried in the RF/IF signal (particularly when the LO is a square wave)? Regardless, every time I need to understand/explain it I have to go either go back & watch your balanced mixer videos, or just grab a NE602 & prove it to myself, before sitting and thinking hard about it...

Maybe a subject for a future video?

[w2aew]

Thanks for these videos, Alan - as always, a nice clear and concise explantion of the subject. I often find myself referring to them as a refresher or referring others to them to save them from my mangled explanations

One thing that's never been particularly intuitive to me is the common use of the NE602 & friends as an RF->IF mixer, particularly when used as a switching downconverter/mixer (e.g. as typical in 10.7MHz/455kHz IF -> 12kHz soundcard SDR adaptors). There's something there that just doesn't stick with me, and I'm not quite sure what - maybe how it manages to convert without destroying the amplitude/phase information carried in the RF/IF signal (particularly when the LO is a square wave)? Regardless, every time I need to understand/explain it I have to go either go back & watch your balanced mixer videos, or just grab a NE602 & prove it to myself, before sitting and thinking hard about it...

Maybe a subject for a future video?

On thing that might help clear this up for you - remember that a square wave is nothing more than a sine wave plus its odd harmonics (properly scaled and phased of course).  Using a square wave as the LO is often done to keep the switching elements out of their linear region (or to traverse the linear region quickly). Depending on the mixer structure, this helps improve LO and RF rejection. The higher order harmonics create additional mixing products, each of which preserves the amplitude/phase modulation of the RF signal.  It is up to the filter after the mixer to select which mixing component you want to use.

[krivx]

Really enjoyed this video, thanks. I've never touched multipliers before but I think I'll have a play around.