Hot-carrier diode substitute

[garyr]

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

 

[garyr]

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
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85140 Skype: Contacts Only | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

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

 

[garyr]

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.



--

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

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators

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.

 

[LM]

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

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.

 

[miso]

As shown in...

http://www.analog-innovations.com/SED/Peak-RF_Detector.pdf

...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.

 

[garyr]

Some followup on the above article comparing 1N4148, 1N270, and
1N5771:
<http://www.diystompboxes.com/smfforum/index.php?topic=90503.0;prev_next=next>
<http://www.cliftonlaboratories.com/diodes_for_rf_probes.htm>
For sensitivity and linearity, 1N270.
For high frequency sensitivity or broadband performance, 1N5771.

--
Jeff Liebermann [email protected]
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

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