Frequently Asked Questions

Actually, “Infrequently Asked Questions” would be more accurate. But would you have clicked on “IAQ”?

What does the name mean?

Arthur C. Clarke said, “Any sufficiently advanced technology is indistinguishable from magic.”

Personally, I still find a wireless garage door opener to be pretty magical, and a color LCD display approaches the miraculous. We who work in technology are privileged to create marvels daily as part of our jobs.

I abbreviated “Sufficiently Advanced Technology” to “SADT” because was already taken. It also lets me have the nifty phone number.

Does that circuit on the front page do anything besides look cool?

In 1968, Barrie Gilbert published “A New Wide-Band Amplifier Technique”. The paper described the “marriage” of two basic transistor circuits, the differential pair and the current mirror, to create a linear, differential, current-mode amplifier. The new amplifier took advantage of the device matching and temperature tracking inherent in the recently-developed monolithic integrated circuit process.

Gilbert Cell schematic

The core of the paper was the “gain cell” shown at the right. A differential current applied at the bottom of the circuit, at the emitters of Q1 and Q4, is amplified into a differential output current at the top. Since the amplifier works in current mode, it is fast. The cell is also well-suited to cascading, since multiple cells can be stacked directly on top of one another.

Gilbert also published a related paper, “A Precise Four-Quadrant Multiplier with Subnano-Second Response”, which expanded on the ideas of the first paper. However, the simpler circuit that is often called a “Gilbert multiplier” was actually patented by H. E. Jones in 1963, as Gilbert himself has been at pains to point out.