Hot-carrier diodes. What became of them?

[G6Tanuki]

In the sixties/early-seventies, I remember there were a number of circuits published for things like VHF or UHF frequency-multipliers/mixers/modulators that used Hot Carrier diodes [the Hewlett-Packard HP2800 series were often specified].

They were not cheap!

You never hear of them these days, and I was wondering what became of the technology?

[Al (astral highway)]

Hi there,

Hasn't the name just been largely replaced over time by the descriptor Schottky diode/ Schottky barrier diode, very commonly in use?

Here's one current offering from On Semiconductor which uses dual terminology in its blurb. 100pS typ switching time.

https://pdf1.alldatasheet.com/datash...MBD301LT1.html

On the other hand I have a couple of the snazzy gold-plated types ex RADAR mixer cct, from the period you are describing, and I imagine expensive at the time, as you say.

I've also used the small-signal types that are available.

Interesting to read here;

Schottky metal–semiconductor junctions are featured in the successors to the 7400 TTL family of logic devices, the 74S, 74LS and 74ALS series, where they are employed as Baker clamps in parallel with the collector-base junctions of the bipolar transistors to prevent their saturation, thereby greatly reducing their turn-off delays.

[G0HZU_JMR]

The modern 1N5711 diode is similar to the classic HP2800 diode. The 1N5711 is available in axial glass or SMD packages and they are cheap to buy. It's the other ones in the HP28xx series that are harder to find now.

I still have a sample bag of 250 of the original HP2800 diodes here. See the HP parts bag below. I've been slowly using them up over the years. I try and use the modern 1N5711 diodes whenever I can. This way I can keep a few of the original 2800 diodes.

When Avago/Broadcom announced that they were going to stop making diodes I bought up quite a few of each type in single, dual and quad in the various 70V, 15V and 4V flavours.

There are still some low voltage, low capacitance alternatives in the BAT series from Infineon. Eg BAT17.

[CambridgeWorks]

The Racal 852 frequency calibrator used HP2800-5082 in the mixer stage. Used to have spares on the van (mobile workshop) for the occasional accident transmitting into it.
Rob

[G6Tanuki]

Aha! I hadn't made the connection between Hot-Carrier diodes and Schottky Diodes...

The reason I asked in the first place was that I'm looking at a couple of 1960s Direct Conversion receiver designs, which use Hot Carrier diodes as the balanced-demodulator, driven with quite a lot of LO power.


I may need to invest in a bunch of 1N5711.

[Al (astral highway)]

Originally Posted by G6Tanuki

I may need to invest in a bunch of 1N5711.

They're super cheap now! You can get them in glass packages that look more similar to the OG ones than the plastic bodies and if aesthetics are important.

Or, there's now SOD-123 packages if you wanted low lead inductance.

Be interesting to hear more about your design!

[G6Tanuki]

That's definitely given me some leads; my design is a free-running 5MHz Colpitts VFO using a 2N3819 FET, with an emitter-follower [BC109] driving a 2N3053 into a pair of top-coupled tuned-circuits based around toroids; the output then goes to a single-balanced hot-carrier-diode mixer where the high-level LO meets the low-level signals from the antenna, which have similarly passed through a toroid-based version of the 'Cohn' bandpass filter [with bottom-indictance coupling of the four toroids].

No RF amplifier!

Essentially a 'switching mixer'. the detected signal then goes to a 3-transistor BC109C amplifier/low-pass-filter, which is where most of the gain and selectivity will happen.

Then a TDA2002 audio amp.

I love playing around with this sort of thing, all wired on tag-boards and small Veroboard offcuts. At least it keeps me from wandering the streets at nights and frightening the locals!

[G0HZU_JMR]

The commonly available version of the 1N5711 is from STMicro. This is usually a blue glass diode. I normally use this diode as an RF detector.

The classic discrete diode to use in a level 7 diode ring mixer was the 1SS97 Schottky diode from NEC but these are long obsolete. Ideally, four matched diodes would be needed. At just 5MHz, you could also consider using 1N4148 silicon diodes in a diode ring mixer (or in a single balanced mixer).