Gilbert Cell Lacks Sullivan
If you’ve ever used an NE602 or similar IC to build a radio, you might have noticed that the datasheet has a “gilbert cell” mixer. What is that? [Electronics for the Inquisitive Experimenter] explains them in a recent video. The gilbert cell is a multiplier, and multiplying two waveforms will work to mix them together.
At the heart of the gilbert cell is essentially three differential amplifiers that share a common current source. The video shows LTSpice simulations of the circuits as he explains them.
One reason these work well on ICs is that they require very closely-matched transistors. In real life, it is hard to get transistors that match exactly. But when they are all on the same slab of silicon, it is fairly straightforward.
What we really like is that after simulating and explaining the circuit, he explains why multipliers mix signals, then builds a real circuit on the bench using discrete transistors and matched transistor arrays. There is a bit of trigonometry in the explanation, but nothing too difficult.
Of course, the most common application of differential amplifiers is the op amp. The NE602 is out of production, sadly, but if you can find any, they make dandy receivers.
youtube.com/embed/mQ36yy7mloA?…