Hot-carrier diode substitute

I want to make a simple rectifier for an RF signal, frequency less than 10 MHz. The schematic below (view with fixed font) is from an article describing a circuit useable with much higher frequencies and used a hot-carrier diode (1N5711). For relative low frequencies would a general purpose diode such as a 1N4148 be adequate?

If a hot-carrier would be necessary I have a problem because I don't have any but I do have a few high speed transistors: BSV52, BSF17, J310. Would the base-emitter or base-collector junction of one of these transistors be a suitable substitute for a hot-carrier diode?

| \ /R2 (20 uA bias current) \ C1 | R2 R3 -||-+-/\/\-+-/\/\- | | v D1 = C2 - | | Gnd Gnd

Reply to
garyr
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Schottkies have lower voltage drops than PN diodes, which helps at any frequency. Low-barrier schottkies are best for rf detectors. Well, after germanium back diodes.

Email me your address and I'll send you a few low-barrier schottkies. I don't know if DC bias helps, but you could try it.

A transistor BE junction is a good diode, but it's still PN so has more voltage drop than a schottly. A jfet diode tends to have a lot of capacitance and it's in series with the channel resistance.

An emitter follower is an interesting detector.

A preamp, or a matching network, would of course improve low-level sensitivity. Or some fancy new detector chip.

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John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    
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Reply to
John Larkin

Less than 10MHz, a 1N4148 should work just fine.

A diff-pair configured as a unity-gain follower, but with just a long-time-constant R/C as the load makes a quite accurate rectifier/detector. (Some PECL gates are easily configured into this arrangement.) ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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Reply to
Jim Thompson

I don't understand your diff-pair detector. Could you elaborate a bit?

Reply to
garyr

I didn't realize that a hot-carrier was a type of schottky diode. I actually have a few SD101BW-TP schottky diodes which, according to the spec, have 2.1 pF capacitance at zero volts and a maximum forward voltage drop at

1 ma of 0.4 volts. They should be OK.

My circuit will have about 30 dB gain ahead of the detector (two MMICs) and an opamp to buffer the output and provide some gain.

Thanks for the info.

Reply to
garyr

They are the same thing.

I

Sounds fine at 10 MHz. For higher frequencies, you can get schottkies down to about 0.2 pF.

OK, lots of signal.

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John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    
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Reply to
John Larkin

Tomorrow. I'm watching a movie on TV right now ;-) ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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Reply to
Jim Thompson

"The Schottky diode (named after German physicist Walter H. Schottky); also known as hot carrier diode is a semiconductor diode with a low forward voltage drop and a very fast switching action."

This might be of interest: I have a roll of 1N270 (germanium) diodes if you want some. Send me a mailing address and I put some in an envelope.

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Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
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Reply to
Jeff Liebermann

0

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I have used a 1N4148 at VHF frequencies. I am sure something like

1N5711 is better or atleast better with low level signals but you get DC out with 1N4148 too.
Reply to
LM

Some followup on the above article comparing 1N4148, 1N270, and

1N5771: For sensitivity and linearity, 1N270. For high frequency sensitivity or broadband performance, 1N5771.
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Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
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Reply to
Jeff Liebermann

[snip]

As shown in...

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...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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Reply to
Jim Thompson

The first circuit is known as the junk buffer.

I'm amazed that got past the patent office. It is basically the well known sat catcher circuit. You find them in LDOs. Then again, they are still patenting sat catchers, even with all the prior art. But nobody is going to court over them.

Reply to
miso

Thanks for the information and the offer. My application is not critical so almost any diode would probably be OK.

Reply to
garyr

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