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basics | Simple transistor NOT gate


There are 19 messages in this thread.

You are currently looking at messages 1 to 10.

Simple transistor NOT gate - Allen Bong - 2008-02-03 02:52:00

Hi,

Is it possible to construct a simple inverter gate using 1 or 2
transistors and resistors?

I tried the circuit below but it doesn't work at all.




                             VCC
                              +
                              |
                              |
                             .-.
                             | |
                             | |4K7
                             '-'
                              |
                              +------o OUTPUT
                              |
                1K_         |/
       INPUT o-|___|----+---|
                        |   |>
                       .-.    |
                       | |    |
                    4K7| |    |
                       '-'    |
                        |     |
                        |     |
                       ===   ==                       GND   GND


Allen









(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

Re: Simple transistor NOT gate - Richard Seriani - 2008-02-03 05:15:00

"Allen Bong" <a...@gmail.com> wrote in message 
news:c...@v67g2000hse.googlegroups.com...
> Hi,
>
> Is it possible to construct a simple inverter gate using 1 or 2
> transistors and resistors?

Allen,

Yes, it is possible, and your circuit should work. When you ground the 
input, the transistor should be in cut-off and the collector voltage should 
be at Vcc. When you apply Vcc to the input, the transistor should saturate 
and the collector voltage should be at zero.

Check all connections and check you transistor. If your ciruit still does 
not work, in what way is it not working? What type of transistor are you 
using? What value of Vcc?

Other options? Google: transistor not gate

Richard



Re: Simple transistor NOT gate - Randy Day - 2008-02-03 09:50:00

Allen Bong wrote:
> 
> Hi,
> 
> Is it possible to construct a simple inverter gate using 1 or 2
> transistors and resistors?
> 
> I tried the circuit below but it doesn't work at all.
> 
>                              VCC
>                               +
>                               |
>                               |
>                              .-.
>                              | |
>                              | |4K7
>                              '-'
>                               |
>                               +------o OUTPUT
>                               |
>                 1K_         |/
>        INPUT o-|___|----+---|
>                         |   |>
>                        .-.    |
>                        | |    |
>                     4K7| |    |
>                        '-'    |
>                         |     |
>                         |     |
>                        ===   ==>                        GND   GND

What do you get at the output when input is at 
ground? At Vcc?

What kind of transistor? How many volts is Vcc?

You may need to select different resistor values 
for a particular transistor type, but it should 
work.

The overall circuit is a classic inverting 
amplifier, used just about everywhere.

Re: Simple transistor NOT gate - Chris - 2008-02-03 11:18:00

On Feb 3, 1:52 am, Allen Bong <allenbsf6...@gmail.com> wrote:
> Hi,
>
> Is it possible to construct a simple inverter gate using 1 or 2
> transistors and resistors?
>
> I tried the circuit below but it doesn't work at all.
>
>                              VCC
>                               +
>                               |
>                               |
>                              .-.
>                              | |
>                              | |4K7
>                              '-'
>                               |
>                               +------o OUTPUT
>                               |
>                 1K_         |/
>        INPUT o-|___|----+---|
>                         |   |>
>                        .-.    |
>                        | |    |
>                     4K7| |    |
>                        '-'    |
>                         |     |
>                         |     |
>                        ===   ===
>                        GND   GND
>
> Allen
>
> (created by AACircuit v1.28.6 beta 04/19/05www.tech-chat.de)

You've described a perfect transistor inverter, that should work for
logic level inputs.  A couple of things to check:

* Make sure you're using an NPN transistor instead of a PNP, a MOSFET,
or something else.

* Recheck your wiring, looking particularly at the pinout of the
transistor.  It's easy to assume EBC when it's ECB, or vice versa.

* Use a voltmeter to actually measure the voltage at the input.  If
you're driving the input from an open collector transistor or gate
output, no current will be injected into the base of your transistor
when your logic level is "high".

If you run through these three, the transistor has to be defective.
Replace it.

You've got the right answer right in front of you.  Make it work.

Cheers
Chris

Re: Simple transistor NOT gate - John Larkin - 2008-02-03 13:29:00

On Sun, 3 Feb 2008 08:18:12 -0800 (PST), Chris <c...@yahoo.com>
wrote:

>On Feb 3, 1:52 am, Allen Bong <allenbsf6...@gmail.com> wrote:
>> Hi,
>>
>> Is it possible to construct a simple inverter gate using 1 or 2
>> transistors and resistors?
>>
>> I tried the circuit below but it doesn't work at all.
>>
>>                              VCC
>>                               +
>>                               |
>>                               |
>>                              .-.
>>                              | |
>>                              | |4K7
>>                              '-'
>>                               |
>>                               +------o OUTPUT
>>                               |
>>                 1K_         |/
>>        INPUT o-|___|----+---|
>>                         |   |>
>>                        .-.    |
>>                        | |    |
>>                     4K7| |    |
>>                        '-'    |
>>                         |     |
>>                         |     |
>>                        ===   ==>>                        GND   GND
>>
>> Allen
>>
>> (created by AACircuit v1.28.6 beta 04/19/05www.tech-chat.de)
>
>You've described a perfect transistor inverter, that should work for
>logic level inputs.  A couple of things to check:
>
>* Make sure you're using an NPN transistor instead of a PNP, a MOSFET,
>or something else.
>
>* Recheck your wiring, looking particularly at the pinout of the
>transistor.  It's easy to assume EBC when it's ECB, or vice versa.
>
>* Use a voltmeter to actually measure the voltage at the input.  If
>you're driving the input from an open collector transistor or gate
>output, no current will be injected into the base of your transistor
>when your logic level is "high".
>
>If you run through these three, the transistor has to be defective.
>Replace it.
>
>You've got the right answer right in front of you.  Make it work.
>
>Cheers
>Chris

Classic RTL gate: should work.

But if you used this to drive another such gate, the second gate would
serious load down the output voltage of the first one. You could
juggle the resistor values to reduce this effect. Like maybe...


>>                              VCC
>>                               +
>>                               |
>>                               |
>>                              .-.
>>                              | |
>>                              | | 1K
>>                              '-'
>>                               |
>>                               +------o OUTPUT
>>                               |
>>                 10K         |/
>>        INPUT o-|___|----+---|
>>                         |   |>
>>                        .-.    |
>>                        | |    |
>>                    open| |    |
>>                        '-'    |
>>                         |     |
>>                         |     |
>>                        ===   ==>>                        GND   GND
>>

John



Re: Simple transistor NOT gate - Allen Bong - 2008-02-03 19:54:00

On Feb 4, 2:29 am, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
> On Sun, 3 Feb 2008 08:18:12 -0800 (PST), Chris <cfoley1...@yahoo.com>
> wrote:
>
>
>
>
>
> >On Feb 3, 1:52 am, Allen Bong <allenbsf6...@gmail.com> wrote:
> >> Hi,
>
> >> Is it possible to construct a simple inverter gate using 1 or 2
> >> transistors and resistors?
>
> >> I tried the circuit below but it doesn't work at all.
>
> >>                              VCC
> >>                               +
> >>                               |
> >>                               |
> >>                              .-.
> >>                              | |
> >>                              | |4K7
> >>                              '-'
> >>                               |
> >>                               +------o OUTPUT
> >>                               |
> >>                 1K_         |/
> >>        INPUT o-|___|----+---|
> >>                         |   |>
> >>                        .-.    |
> >>                        | |    |
> >>                     4K7| |    |
> >>                        '-'    |
> >>                         |     |
> >>                         |     |
> >>                        ===   ===
> >>                        GND   GND
>
> >> Allen
>
> >> (created by AACircuit v1.28.6 beta 04/19/05www.tech-chat.de)
>
> >You've described a perfect transistor inverter, that should work for
> >logic level inputs.  A couple of things to check:
>
> >* Make sure you're using an NPN transistor instead of a PNP, a MOSFET,
> >or something else.
>
> >* Recheck your wiring, looking particularly at the pinout of the
> >transistor.  It's easy to assume EBC when it's ECB, or vice versa.
>
> >* Use a voltmeter to actually measure the voltage at the input.  If
> >you're driving the input from an open collector transistor or gate
> >output, no current will be injected into the base of your transistor
> >when your logic level is "high".
>
> >If you run through these three, the transistor has to be defective.
> >Replace it.
>
> >You've got the right answer right in front of you.  Make it work.
>
> >Cheers
> >Chris
>
> Classic RTL gate: should work.
>
> But if you used this to drive another such gate, the second gate would
> serious load down the output voltage of the first one. You could
> juggle the resistor values to reduce this effect. Like maybe...
>
>
>
>
>
> >>                              VCC
> >>                               +
> >>                               |
> >>                               |
> >>                              .-.
> >>                              | |
> >>                              | | 1K
> >>                              '-'
> >>                               |
> >>                               +------o OUTPUT
> >>                               |
> >>                 10K         |/
> >>        INPUT o-|___|----+---|
> >>                         |   |>
> >>                        .-.    |
> >>                        | |    |
> >>                    open| |    |
> >>                        '-'    |
> >>                         |     |
> >>                         |     |
> >>                        ===   ===
> >>                        GND   GND
>
> John- Hide quoted text -
>
> - Show quoted text -- Hide quoted text -
>
> - Show quoted text -

Thanks very much Richard, Randy, Chris & John,

The gate was used to replace a 74LS04 TTL inverter used between the
output of 74LS138 and the LE input of a 74LS373 latch.  The clock was
about 1.8Mhz.  During a high the transistor conducts fine but during a
low input of short duration, I would not be able to get a high with my
logic probe nor the LE is triggered.  The Vcc is 5V and the transistor
is a Japanese 2SC945 general purpose transistor.

I checked with google for a transistor NOT gate and it used 1K at
collector and 10K for the base and input.  There was no resistor
between Base and Emitter.  And I tried that circuit, it doesn't work
too.  Where can I get the schematics for a RTL or DTL not gate?

TIA and regards,

Allen

Re: Simple transistor NOT gate - Allen Bong - 2008-02-03 20:11:00

On Feb 4, 8:54 am, Allen Bong <allenbsf6...@gmail.com> wrote:
> On Feb 4, 2:29 am, John Larkin
>
>
>
>
>
> <jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
> > On Sun, 3 Feb 2008 08:18:12 -0800 (PST), Chris <cfoley1...@yahoo.com>
> > wrote:
>
> > >On Feb 3, 1:52 am, Allen Bong <allenbsf6...@gmail.com> wrote:
> > >> Hi,
>
> > >> Is it possible to construct a simple inverter gate using 1 or 2
> > >> transistors and resistors?
>
> > >> I tried the circuit below but it doesn't work at all.
>
> > >>                              VCC
> > >>                               +
> > >>                               |
> > >>                               |
> > >>                              .-.
> > >>                              | |
> > >>                              | |4K7
> > >>                              '-'
> > >>                               |
> > >>                               +------o OUTPUT
> > >>                               |
> > >>                 1K_         |/
> > >>        INPUT o-|___|----+---|
> > >>                         |   |>
> > >>                        .-.    |
> > >>                        | |    |
> > >>                     4K7| |    |
> > >>                        '-'    |
> > >>                         |     |
> > >>                         |     |
> > >>                        ===   ===
> > >>                        GND   GND
>
> > >> Allen
>
> > >> (created by AACircuit v1.28.6 beta 04/19/05www.tech-chat.de)
>
> > >You've described a perfect transistor inverter, that should work for
> > >logic level inputs.  A couple of things to check:
>
> > >* Make sure you're using an NPN transistor instead of a PNP, a MOSFET,
> > >or something else.
>
> > >* Recheck your wiring, looking particularly at the pinout of the
> > >transistor.  It's easy to assume EBC when it's ECB, or vice versa.
>
> > >* Use a voltmeter to actually measure the voltage at the input.  If
> > >you're driving the input from an open collector transistor or gate
> > >output, no current will be injected into the base of your transistor
> > >when your logic level is "high".
>
> > >If you run through these three, the transistor has to be defective.
> > >Replace it.
>
> > >You've got the right answer right in front of you.  Make it work.
>
> > >Cheers
> > >Chris
>
> > Classic RTL gate: should work.
>
> > But if you used this to drive another such gate, the second gate would
> > serious load down the output voltage of the first one. You could
> > juggle the resistor values to reduce this effect. Like maybe...
>
> > >>                              VCC
> > >>                               +
> > >>                               |
> > >>                               |
> > >>                              .-.
> > >>                              | |
> > >>                              | | 1K
> > >>                              '-'
> > >>                               |
> > >>                               +------o OUTPUT
> > >>                               |
> > >>                 10K         |/
> > >>        INPUT o-|___|----+---|
> > >>                         |   |>
> > >>                        .-.    |
> > >>                        | |    |
> > >>                    open| |    |
> > >>                        '-'    |
> > >>                         |     |
> > >>                         |     |
> > >>                        ===   ===
> > >>                        GND   GND
>
> > John- Hide quoted text -
>
> > - Show quoted text -- Hide quoted text -
>
> > - Show quoted text -
>
> Thanks very much Richard, Randy, Chris & John,
>
> The gate was used to replace a 74LS04 TTL inverter used between the
> output of 74LS138 and the LE input of a 74LS373 latch.  The clock was
> about 1.8Mhz.  During a high the transistor conducts fine but during a
> low input of short duration, I would not be able to get a high with my
> logic probe nor the LE is triggered.  The Vcc is 5V and the transistor
> is a Japanese 2SC945 general purpose transistor.
>
> I checked with google for a transistor NOT gate and it used 1K at
> collector and 10K for the base and input.  There was no resistor
> between Base and Emitter.  And I tried that circuit, it doesn't work
> too.  Where can I get the schematics for a RTL or DTL not gate?
>
> TIA and regards,
>
> Allen- Hide quoted text -
>
> - Show quoted text -

I have got the datasheet of 2sc945 at

http://www.ortodoxism.ro/datasheets2/8/0u9h25xojqxp8qwzrfi8kxtjsswy.pdf

and the RTL inverter gate at

http://www.play-hookey.com/digital/experiments/rtl_inverter.html

Should I used HFE1 or HFE2 for the current gain of the 2sc945 or
should I get a 2N4124 to make the circuit work?

Allen



Re: Simple transistor NOT gate - Tim Wescott - 2008-02-03 20:19:00

On Sun, 03 Feb 2008 16:54:44 -0800, Allen Bong wrote:

> On Feb 4, 2:29 am, John Larkin
> <jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
>> On Sun, 3 Feb 2008 08:18:12 -0800 (PST), Chris <cfoley1...@yahoo.com>
>> wrote:
>>
>>
>>
>>
>>
>> >On Feb 3, 1:52 am, Allen Bong <allenbsf6...@gmail.com> wrote:
>> >> Hi,
>>
>> >> Is it possible to construct a simple inverter gate using 1 or 2
>> >> transistors and resistors?
>>
>> >> I tried the circuit below but it doesn't work at all.
>>
>> >>                              VCC
>> >>                               +
>> >>                               |
>> >>                               |
>> >>                              .-.
>> >>                              | |
>> >>                              | |4K7
>> >>                              '-'
>> >>                               |
>> >>                               +------o OUTPUT
>> >>                               |
>> >>                 1K_         |/
>> >>        INPUT o-|___|----+---|
>> >>                         |   |>
>> >>                        .-.    |
>> >>                        | |    |
>> >>                     4K7| |    |
>> >>                        '-'    |
>> >>                         |     |
>> >>                         |     |
>> >>                        ===   ==>> >>                        GND   GND
>>
>> >> Allen
>>
>> >> (created by AACircuit v1.28.6 beta 04/19/05www.tech-chat.de)
>>
>> >You've described a perfect transistor inverter, that should work for
>> >logic level inputs.  A couple of things to check:
>>
>> >* Make sure you're using an NPN transistor instead of a PNP, a MOSFET,
>> >or something else.
>>
>> >* Recheck your wiring, looking particularly at the pinout of the
>> >transistor.  It's easy to assume EBC when it's ECB, or vice versa.
>>
>> >* Use a voltmeter to actually measure the voltage at the input.  If
>> >you're driving the input from an open collector transistor or gate
>> >output, no current will be injected into the base of your transistor
>> >when your logic level is "high".
>>
>> >If you run through these three, the transistor has to be defective.
>> >Replace it.
>>
>> >You've got the right answer right in front of you.  Make it work.
>>
>> >Cheers
>> >Chris
>>
>> Classic RTL gate: should work.
>>
>> But if you used this to drive another such gate, the second gate would
>> serious load down the output voltage of the first one. You could juggle
>> the resistor values to reduce this effect. Like maybe...
>>
>>
>>
>>
>>
>> >>                              VCC
>> >>                               +
>> >>                               |
>> >>                               |
>> >>                              .-.
>> >>                              | |
>> >>                              | | 1K
>> >>                              '-'
>> >>                               |
>> >>                               +------o OUTPUT
>> >>                               |
>> >>                 10K         |/
>> >>        INPUT o-|___|----+---|
>> >>                         |   |>
>> >>                        .-.    |
>> >>                        | |    |
>> >>                    open| |    |
>> >>                        '-'    |
>> >>                         |     |
>> >>                         |     |
>> >>                        ===   ==>> >>                        GND   GND
>>
>> John- Hide quoted text -
>>
>> - Show quoted text -- Hide quoted text -
>>
>> - Show quoted text -
> 
> Thanks very much Richard, Randy, Chris & John,
> 
> The gate was used to replace a 74LS04 TTL inverter used between the
> output of 74LS138 and the LE input of a 74LS373 latch.  The clock was
> about 1.8Mhz.  During a high the transistor conducts fine but during a
> low input of short duration, I would not be able to get a high with my
> logic probe nor the LE is triggered.  The Vcc is 5V and the transistor
> is a Japanese 2SC945 general purpose transistor.
> 
> I checked with google for a transistor NOT gate and it used 1K at
> collector and 10K for the base and input.  There was no resistor between
> Base and Emitter.  And I tried that circuit, it doesn't work too.  Where
> can I get the schematics for a RTL or DTL not gate?
> 
> TIA and regards,
> 
> Allen

Plain 'ol transistor circuits can be slooow if you aren't careful.  You 
should either use a smaller (220 ohm?) resistor on the base, or you 
should use a 220 in series with a 1k in parallel with a cap -- something 
between 100pF and 1nF should do, but I refuse to go through the math in 
my head.

You can get Tiny Logic inverters -- I assume you are purposely avoiding 
surface mount parts?

-- 
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html

Re: Simple transistor NOT gate - Allen Bong - 2008-02-03 20:46:00

On Feb 4, 9:19 am, Tim Wescott <t...@seemywebsite.com> wrote:
> On Sun, 03 Feb 2008 16:54:44 -0800, Allen Bong wrote:
> > On Feb 4, 2:29 am, John Larkin
> > <jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
> >> On Sun, 3 Feb 2008 08:18:12 -0800 (PST), Chris <cfoley1...@yahoo.com>
> >> wrote:
>
> >> >On Feb 3, 1:52 am, Allen Bong <allenbsf6...@gmail.com> wrote:
> >> >> Hi,
>
> >> >> Is it possible to construct a simple inverter gate using 1 or 2
> >> >> transistors and resistors?
>
> >> >> I tried the circuit below but it doesn't work at all.
>
> >> >>                              VCC
> >> >>                               +
> >> >>                               |
> >> >>                               |
> >> >>                              .-.
> >> >>                              | |
> >> >>                              | |4K7
> >> >>                              '-'
> >> >>                               |
> >> >>                               +------o OUTPUT
> >> >>                               |
> >> >>                 1K_         |/
> >> >>        INPUT o-|___|----+---|
> >> >>                         |   |>
> >> >>                        .-.    |
> >> >>                        | |    |
> >> >>                     4K7| |    |
> >> >>                        '-'    |
> >> >>                         |     |
> >> >>                         |     |
> >> >>                        ===   ===
> >> >>                        GND   GND
>
> >> >> Allen
>
> >> >> (created by AACircuit v1.28.6 beta 04/19/05www.tech-chat.de)
>
> >> >You've described a perfect transistor inverter, that should work for
> >> >logic level inputs.  A couple of things to check:
>
> >> >* Make sure you're using an NPN transistor instead of a PNP, a MOSFET,
> >> >or something else.
>
> >> >* Recheck your wiring, looking particularly at the pinout of the
> >> >transistor.  It's easy to assume EBC when it's ECB, or vice versa.
>
> >> >* Use a voltmeter to actually measure the voltage at the input.  If
> >> >you're driving the input from an open collector transistor or gate
> >> >output, no current will be injected into the base of your transistor
> >> >when your logic level is "high".
>
> >> >If you run through these three, the transistor has to be defective.
> >> >Replace it.
>
> >> >You've got the right answer right in front of you.  Make it work.
>
> >> >Cheers
> >> >Chris
>
> >> Classic RTL gate: should work.
>
> >> But if you used this to drive another such gate, the second gate would
> >> serious load down the output voltage of the first one. You could juggle
> >> the resistor values to reduce this effect. Like maybe...
>
> >> >>                              VCC
> >> >>                               +
> >> >>                               |
> >> >>                               |
> >> >>                              .-.
> >> >>                              | |
> >> >>                              | | 1K
> >> >>                              '-'
> >> >>                               |
> >> >>                               +------o OUTPUT
> >> >>                               |
> >> >>                 10K         |/
> >> >>        INPUT o-|___|----+---|
> >> >>                         |   |>
> >> >>                        .-.    |
> >> >>                        | |    |
> >> >>                    open| |    |
> >> >>                        '-'    |
> >> >>                         |     |
> >> >>                         |     |
> >> >>                        ===   ===
> >> >>                        GND   GND
>
> >> John- Hide quoted text -
>
> >> - Show quoted text -- Hide quoted text -
>
> >> - Show quoted text -
>
> > Thanks very much Richard, Randy, Chris & John,
>
> > The gate was used to replace a 74LS04 TTL inverter used between the
> > output of 74LS138 and the LE input of a 74LS373 latch.  The clock was
> > about 1.8Mhz.  During a high the transistor conducts fine but during a
> > low input of short duration, I would not be able to get a high with my
> > logic probe nor the LE is triggered.  The Vcc is 5V and the transistor
> > is a Japanese 2SC945 general purpose transistor.
>
> > I checked with google for a transistor NOT gate and it used 1K at
> > collector and 10K for the base and input.  There was no resistor between
> > Base and Emitter.  And I tried that circuit, it doesn't work too.  Where
> > can I get the schematics for a RTL or DTL not gate?
>
> > TIA and regards,
>
> > Allen
>
> Plain 'ol transistor circuits can be slooow if you aren't careful.  You
> should either use a smaller (220 ohm?) resistor on the base, or you
> should use a 220 in series with a 1k in parallel with a cap -- something
> between 100pF and 1nF should do, but I refuse to go through the math in
> my head.
>
> You can get Tiny Logic inverters -- I assume you are purposely avoiding
> surface mount parts?
>
> --
> Tim Wescott
> Control systems and communications consultinghttp://www.wescottdesign.com
>
> Need to learn how to apply control theory in your embedded system?
> "Applied Control Theory for Embedded Systems" by Tim Wescott
> Elsevier/Newnes,http://www.wescottdesign.com/actfes/actfes.html- Hide quoted text -
>
> - Show quoted text -

Is this the circuit you have in mind?




                 VCC
                  |
                 .-.
                 | |
                 | |1K
                 '-'
                  |
        10k       +------o
        ___     |/
     o-|___|-+ -|
             |  |>
            .-.   |
            | |   |
         220| |  ===
            '-'  GND
             |
             +---+
             |   |
            .-.  |
            | | ---
          1k| | ---1n
            '-'  |
             |   |
             +---+
             |
            ===
            GND


(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

Yes, this is just a hobby & fun project and I dont have the gears to
solder a SMD.  I am constructing the circuit on a breadboard and if it
works, I would solder it onto a stripboard.

I saw the inverter SMD on the back of the databook.  It was made by
Toshiba and part number is TC4S69F.  It was a 1989 databook.

Allen


Re: Simple transistor NOT gate - Bob Monsen - 2008-02-03 22:21:00

Alan:
   Your transtor is saturating when on, and it is probably very slow to come 
out of saturation. Try putting a diode from base to collector; that will 
keep it from saturating. Here is the circuit:

VCC --------------------------.
                              |
                              |
                             .-.
                             | | 10k
                             | |
                             '-'
                              |
                              |
                    .--->|----o----- out
                    |         |
                    |         |
                    |         |
            1k      |         |
            ___     |       |/
 in -------|___|----o-------|
                            |>
                              |
                              |
GND --------------------------'
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

This trick is called a 'baker clamp' for some reason. The diode prevents the 
transistor from saturating, thereby increasing the speed at which it can 
turn off. This circuit probably won't do more than a few MHz, but you never 
know.

Regards,
 Bob Monsen 


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