current conveyors

[unclejed613]

i've been seeing a lot of analog design centered around this "device" lately. it seems the current conveyor is the new "building block" as the op amp was years ago. i'll post later when i find a particular schematic i'm looking for, but these devices seem to be a series of cascaded current mirrors. right now i have to leave for work...

[CBS240]

There are some transistor arrays from Advanced Linear Devices, ALD1116 and ALD1117 or (ALD1105 and 1103 complementary) could be used for something like this. I bet one could make a decent VAS using current mirror multiplication. Simply cascode if more than 10Vds needed.

[mlloyd1]

some years ago, there was one that generated some interest before the company went "away". i wonder if wadia bought the rights to the design or something? the part number was PA630 and PA630A. allegedly, these parts made nice i-v converters for cd players and such.
alas, that was one sample i never got ...

mlloyd1

[forr]

Hi unclejed613,

---it seems the current conveyor is the new "building block" as the op amp was years ago.---

That is what was thought when first current conveyors appear, I should say about twenty years ago. Concept and designing with them are as simple as with op-amp, even easier. However, if objective performances are sought, they're not the winners.
However a fascinating use of them is found in the error correction of Jan Didden's Pax amplifier.
I have collected some documentation about them, email me if you're interested.

[unclejed613]

ok, here's the circuit i was looking for. it would be interesting to build one of these with discrete components and experiment with it. from what i've been reading about CCs, the bandwidth is only limited by the Ft of the transistors. i'll have to look further to see how they're used as amplifiers, etc...

Ib at the left is an external current source. X and Y are inputs (but Y can also serve as an output i think) and the Z terminals are outputs. i've seen the equivalent circuit of this drawn as a transistor with -Z as the collector, and Y as the emitter and X as the base. it would be interesting to use this as a "transistor" with an inverting and noninverting "collector".

i wouldn't want to use a transistor array for this as most of them contain a parasitic substrate diode, which requires the substrate to be reverse biased to prevent damage to the device.

[mlloyd1]

here's a little more on the device i was referring. at the time, they used a high speed process to make good pnp as well as npn parts.

Circuits and systems tutorials - Google Books

Originally Posted by mlloyd1

some years ago, there was one that generated some interest before the company went "away". i wonder if wadia bought the rights to the design or something? the part number was PA630 and PA630A. allegedly, these parts made nice i-v converters for cd players and such.
alas, that was one sample i never got ...

mlloyd1

[CBS240]

Originally Posted by unclejed613

i wouldn't want to use a transistor array for this as most of them contain a parasitic substrate diode, which requires the substrate to be reverse biased to prevent damage to the device.

THAT 300 series matched arrays do not have a diode. It consists of 4 separate dies and do not share the same substrate. Pin 4 is connected to pin 11 internally as the 'substrate' but it should still be referenced somewhere to reduce noise.

[unclejed613]

i was thinking of the nat-semi and TI devices

[tiefbassuebertr]

check also out the PAX amplifier from Jan Didden (diyaudio member "Jannemann")
An Amplifier without feedback called Pax, What about Vitus SS-101?

[unclejed613]

interesting use of a CC for feedback. i didn't quite appreciate the later use of spice behavioral sources for an amplifier though. B sources are "ideal" devices. i can make a perfectly linear amplifier from a B source, if there were such a thing in real life. i'll probably get some time later this week to experiment with the schematic i found in EDN magazine. i've been working on some other projects.