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'[PICLIST] [EE] Buffer to drive T1CLK at 5.5Mhz fro'
2002\01\16@070746 by Jinx

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> It was overly complex due to me trying to get unnecessarily
> fast edges. Martin Peach's idea of just using a 74HC gate
> is working well (with a x2 bipolar amp infront of it !)

If the input is a steady 1.2V you should be able to use one
of the other gates in its linear region as an amplifier

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2002\01\16@073414 by Peter Onion

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On 16-Jan-02 Jinx wrote:
>> It was overly complex due to me trying to get unnecessarily
>> fast edges. Martin Peach's idea of just using a 74HC gate
>> is working well (with a x2 bipolar amp infront of it !)
>
> If the input is a steady 1.2V you should be able to use one
> of the other gates in its linear region as an amplifier

I assume you mean by putting a suitable resistor between the o/p and i/p of the
gate ?  I did think about this, but since I'm using a schmitt trigger (because
I have a spare gate in a 74HC14 that is used for other things) I didn't try it
as I don't think you can bias schmitt trigger gates into a "linear" region, but
I may be wrong.

I'll give it a try tonight and let you know if it works or not.

Peter.



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Date: 16-Jan-02
Time: 12:20:56

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2002\01\16@075036 by Jinx

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> as I don't think you can bias schmitt trigger gates into
> a "linear" region

> I'll give it a try tonight and let you know if it works or not.

ST probably won't  ;-(

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2002\01\17@095844 by Roman Black

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Peter Onion wrote:
>
> On 16-Jan-02 Jinx wrote:
> >> It was overly complex due to me trying to get unnecessarily
> >> fast edges. Martin Peach's idea of just using a 74HC gate
> >> is working well (with a x2 bipolar amp infront of it !)
> >
> > If the input is a steady 1.2V you should be able to use one
> > of the other gates in its linear region as an amplifier
>
> I assume you mean by putting a suitable resistor between the o/p and i/p of the
> gate ?  I did think about this, but since I'm using a schmitt trigger (because
> I have a spare gate in a 74HC14 that is used for other things) I didn't try it
> as I don't think you can bias schmitt trigger gates into a "linear" region, but
> I may be wrong.
>
> I'll give it a try tonight and let you know if it works or not.


Use a 2 resistor divider to set the schmitt input
to the mid-point between the HI and LO thresholds,
then capacitor couple the ac signal which should
then work the schmitt. 2 resistors 1 cap. :o)
-Roman

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2002\01\18@022354 by Dwayne Reid

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At 01:51 AM 1/18/02 +1100, Roman Black wrote:

>Use a 2 resistor divider to set the schmitt input
>to the mid-point between the HI and LO thresholds,
>then capacitor couple the ac signal which should
>then work the schmitt. 2 resistors 1 cap. :o)

There is an old trick that allows automatic setting of the bias point: use
1 section of schmitt trigger inverter as a high speed oscillator, then use
large value resistors to couple the input of that (osc) inverter to the
inputs of the remaining inverters in the package.  The signal at the input
of the oscillator section ranges from VinH to VinL and the input
capacitance of the inverters actually being used filters out (integrates)
the high frequency signal, leaving a DC voltage exactly midway between VinH
and VinL.

dwayne



Dwayne Reid   <dwaynerspamspam_OUTplanet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
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2002\01\18@054002 by Peter Onion

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On 16-Jan-02 Peter Onion wrote:

> I assume you mean by putting a suitable resistor between the o/p and i/p of
> the
> gate ?  I did think about this, but since I'm using a schmitt trigger
> (because
> I have a spare gate in a 74HC14 that is used for other things) I didn't try
> it
> as I don't think you can bias schmitt trigger gates into a "linear" region,
> but
> I may be wrong.
>
> I'll give it a try tonight and let you know if it works or not.

Well I spent a few hours playing with this idea last night.

It seems that is it impossible to get a 74HC11 inverter into it's linear region
without it oscillating at some high frequency.  I tried all sorts of things to
calm it down, higher and lower feedback resistors, small and large C, ferrite
beads etc etc etc...

In the end I gave up and went back to using the x2 bipolar amp infront of a
schmitt trigger.

Peter

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2002\01\19@094836 by Roman Black

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Peter Onion wrote:
{Quote hidden}

That's why you use a schmidt trigger inverter
like a 74HC14, the hysteresis lets you bias it
with 2 resistors between the input thresholds,
and you can drive it hi/low with the smallest
AC signal that the threshold delta allows.
1.2v AC should be do-able.
I did suggest this a couple posts back. :o)
-Roman

>
> In the end I gave up and went back to using the x2 bipolar amp infront of a
> schmitt trigger.

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