Zener diodes work fine as varicaps, at least at HF. The lower the zener
voltage and higher the power dissipation rating, the higher the C. As
someone else mentioned, transistor emitter-base junctions can be used as
either zeners (typical zener voltage around 5 volts) or varicaps.

A zener can be used as a broadband noise source. I've had the best luck
with zeners of 10 - 15 volt breakdown, with around 100 uA current. Some
are noisier than others, and they often have a critical current where
the noise is the greatest.

Tektronix used selected transistors to generate high voltage (~100
volts) fast steps (~100 ps rise time if I recall correctly) by
avalanching the collector. Some fraction of some common transistor types
worked satisfactorily in this application.

1N914 type diodes can be used as step recovery diodes to generate a step
with about a ns risetime -- maybe faster with a chip component and some
care. This could be the basis of a broadband harmonic generator.

Roy Lewallen, W7EL

Roy Lewallen wrote:
Zener diodes work fine as varicaps, at least at HF. The lower the
zener voltage and higher the power dissipation rating, the higher the
C. As someone else mentioned, transistor emitter-base junctions can
be used as either zeners (typical zener voltage around 5 volts) or
varicaps.
A zener can be used as a broadband noise source. I've had the best
luck with zeners of 10 - 15 volt breakdown, with around 100 uA
current. Some are noisier than others, and they often have a critical
current where the noise is the greatest.

Tektronix used selected transistors to generate high voltage (~100
volts) fast steps (~100 ps rise time if I recall correctly) by
avalanching the collector. Some fraction of some common transistor
types worked satisfactorily in this application.

1N914 type diodes can be used as step recovery diodes to generate a
step with about a ns risetime -- maybe faster with a chip component
and some care. This could be the basis of a broadband harmonic
generator.
Roy Lewallen, W7EL

At a leading Ultrasonic flaw detector company we used simple low frequency
Motorola sot23 transistors in avalance mode for making a nice pulse
generator for 100MHz probes. These were better than the Zetex avalance
specified transistors.
--
ciao Ban
Apricale, Italy

Ban wrote:

Roy Lewallen wrote:

Zener diodes work fine as varicaps, at least at HF. The lower the
zener voltage and higher the power dissipation rating, the higher the
C. As someone else mentioned, transistor emitter-base junctions can
be used as either zeners (typical zener voltage around 5 volts) or
varicaps.
A zener can be used as a broadband noise source. I've had the best
luck with zeners of 10 - 15 volt breakdown, with around 100 uA
current. Some are noisier than others, and they often have a critical
current where the noise is the greatest.

Tektronix used selected transistors to generate high voltage (~100
volts) fast steps (~100 ps rise time if I recall correctly) by
avalanching the collector. Some fraction of some common transistor
types worked satisfactorily in this application.

1N914 type diodes can be used as step recovery diodes to generate a
step with about a ns risetime -- maybe faster with a chip component
and some care. This could be the basis of a broadband harmonic
generator.
Roy Lewallen, W7EL


At a leading Ultrasonic flaw detector company we used simple low frequency
Motorola sot23 transistors in avalance mode for making a nice pulse
generator for 100MHz probes. These were better than the Zetex avalance
specified transistors.

2N2369 for fast pulses.
2N2222 and even 2N2219 works, but a bit slower and they requiring more
voltage to avalance, but still 1nS rt
The Zetex are slower but can deliver much more current (up to 60A, ZTX
415 family).

Jorgen

Hello Jorgen,

Jorgen Lund-Nielsen wrote:

[.....]
2N2369 for fast pulses.

btw, do you know a standard complementary pnp-transistor for the 2N2369,
such like 2N3905 but with higher ft and less feedback capacitance? It
seems that the manufactorers have almost no data on their internet pages.

mfg. Winfried

On Sat, 26 Nov 2005 21:41:06 +0100, Winfried Salomon
wrote:

Hello Jorgen,

Jorgen Lund-Nielsen wrote:

[.....]
2N2369 for fast pulses.

btw, do you know a standard complementary pnp-transistor for the 2N2369,
such like 2N3905 but with higher ft and less feedback capacitance? It
seems that the manufactorers have almost no data on their internet pages.

mfg. Winfried

A 2N2369 is a gold-doped NPN, gold-doped to kill storage time and
improve recovery from saturation. I don't recall any PNP device with
gold-doping... or the equivalent.

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

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

Hello Jim,

Jim Thompson wrote:
[...]
btw, do you know a standard complementary pnp-transistor for the 2N2369,
such like 2N3905 but with higher ft and less feedback capacitance? It
seems that the manufactorers have almost no data on their internet pages.

[...]


A 2N2369 is a gold-doped NPN, gold-doped to kill storage time and
improve recovery from saturation. I don't recall any PNP device with
gold-doping... or the equivalent.

thank you, then I suppose the 2N3905 oder 2N2905 are fitting for a large
signal amplifier.

mfg. Winfried

Jim Thompson wrote:
On Sat, 26 Nov 2005 21:41:06 +0100, Winfried Salomon
wrote:

Hello Jorgen,

Jorgen Lund-Nielsen wrote:

[.....]
2N2369 for fast pulses.

btw, do you know a standard complementary pnp-transistor for the 2N2369,
such like 2N3905 but with higher ft and less feedback capacitance? It
seems that the manufactorers have almost no data on their internet pages.

mfg. Winfried

A 2N2369 is a gold-doped NPN, gold-doped to kill storage time and
improve recovery from saturation. I don't recall any PNP device with
gold-doping... or the equivalent.

...Jim Thompson

National Semi's (now Fairchild) 2n5771 was a gold-doped PNP.
ft=850MHz. For avalanche mode one might try the lower-Vce-rated
PN3640 (12v), or PN3639 (6v).

I might even have notes on this. I tested/compared various BJTs in
avalanche mode some years ago, trying to find the "best." ISTR picking
the 2n2369, both because it was fast, and because it avalanched
reliably where other types wouldn't.

James Arthur

On 30 Nov 2005 14:32:29 -0800, wrote:


Jim Thompson wrote:
On Sat, 26 Nov 2005 21:41:06 +0100, Winfried Salomon
wrote:

Hello Jorgen,

Jorgen Lund-Nielsen wrote:

[.....]
2N2369 for fast pulses.

btw, do you know a standard complementary pnp-transistor for the 2N2369,
such like 2N3905 but with higher ft and less feedback capacitance? It
seems that the manufactorers have almost no data on their internet pages.

mfg. Winfried

A 2N2369 is a gold-doped NPN, gold-doped to kill storage time and
improve recovery from saturation. I don't recall any PNP device with
gold-doping... or the equivalent.

...Jim Thompson

National Semi's (now Fairchild) 2n5771 was a gold-doped PNP.
ft=850MHz. For avalanche mode one might try the lower-Vce-rated
PN3640 (12v), or PN3639 (6v).

I might even have notes on this. I tested/compared various BJTs in
avalanche mode some years ago, trying to find the "best." ISTR picking
the 2n2369, both because it was fast, and because it avalanched
reliably where other types wouldn't.

James Arthur


Hi, James,

Interestingly, the best avalanchers aren't usually super-fast
transistors, but old klunky things. The Zetex avalanche transistors
have lowish Ft's and are made in Russia, maybe on an old process.

John

Winfried Salomon wrote:
Hello Jorgen,

Jorgen Lund-Nielsen wrote:

[.....]

2N2369 for fast pulses.


btw, do you know a standard complementary pnp-transistor for the 2N2369,
such like 2N3905 but with higher ft and less feedback capacitance? It
seems that the manufactorers have almost no data on their internet pages.

mfg. Winfried

Maybe 2N4261 ? Have not looked into the datasheet, but as i remember,
i have seen them sometimes in complementary with the 2N2369

Jorgen

Hello Jorgen,

Jorgen Lund-Nielsen wrote:



Winfried Salomon wrote:

Hello Jorgen,

Jorgen Lund-Nielsen wrote:

[.....]

2N2369 for fast pulses.



btw, do you know a standard complementary pnp-transistor for the
2N2369, such like 2N3905 but with higher ft and less feedback
capacitance? It seems that the manufactorers have almost no data on
their internet pages.

mfg. Winfried


Maybe 2N4261 ? Have not looked into the datasheet, but as i remember,
i have seen them sometimes in complementary with the 2N2369


the problem is, that it is an rf-transistor and can't be driven at
30V/0.2A, I found a complementary in an old table KTT, the 2N2894A, but
it also has max. 12V, so I find no other than the 2N3906.

If I simulate with the 2N3906, the frequency response is not worse than
with the 2N2894A.

mfg. Winfried