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I was looking at using the OPA860 for a voltage controlled load. Reading in the OPA860 datasheet it says:

The OPA860 combines a high-performance buffer with a transconductance section. This transconductance section is discussed in the OTA The buffer section of the OPA860 is an 1600MHz, (Operational Transconductance Amplifier) section of 4000V/μs closed-loop buffer that can be used as a this data sheet. Over the years and depending on the building block for AGC amplifiers, LED driver circuit, writer, the OTA section of an op amp has been integrator for fast pulse, fast control loop amplifiers, referred to as a Diamond Transistor, and control amplifiers for capacitive sensors and Voltage-Controlled Current source, Transconductor, active filters.

Are they achieving the transconductance with regular boring silicon tech (which is probably the case) or something else?

My main reason for asking the question is because its a cool part (low noise and transconductance), and because even though I suspect there is no secret sauce maybe there is, it also says ±1.2V differential input which I thought was interesting.

enter image description here

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  • \$\begingroup\$ ti.com/lit/an/sboa071/sboa071.pdf \$\endgroup\$
    – user3528438
    Commented Mar 24, 2017 at 18:19
  • \$\begingroup\$ I glossed over that because the other part looked better, Thanks \$\endgroup\$
    – Voltage Spike ♦
    Commented Mar 24, 2017 at 18:24
  • \$\begingroup\$ It is traditionally referred to as a diamond buffer. Extremely high speed current amplifier. \$\endgroup\$
    – dannyf
    Commented Mar 24, 2017 at 19:02
  • \$\begingroup\$ Actually, to answer my own question it is "a diamond transistor", but a diamond transistor is a configuration of transistors, not a transistor made of diamonds. "The monolithic integrated circuit OPA660 uses the Dia- mond structure to act as an ideal transistor" \$\endgroup\$
    – Voltage Spike ♦
    Commented Mar 25, 2017 at 5:47

2 Answers 2

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It's a particular complementary BJT circuit arrangement as so:

enter image description here

Which behaves similarly to transistor that does not have a Vbe offset and biasing issues, as explained in the link which @user3528438 also provided in a comment.

It's made with Burr-Brown/TI's high performance silicon analog IC process, not carbon-based.

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    \$\begingroup\$ It also doesn't have polarity; it takes negative "base" voltage to give negative "collector" current. \$\endgroup\$
    – Whit3rd
    Commented Mar 24, 2017 at 20:01
  • \$\begingroup\$ Looks like a section of a nice pin-driver to me, except for the low output compliance voltage. Pricey! \$\endgroup\$
    – jonk
    Commented Mar 24, 2017 at 21:37
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This document from TI says it is a particular configuration rather than exotic materials

I also found other references to the diamond structure that also refer to it being a particular circuit configuration.

But, transistors made of diamond appear to be real thing, also. Only found references to research, though. No commercial products that I could find (though they might exist, I just didn't make a thorough search.

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