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'[EE] Long tailed pair, sort of.'
2016\09\19@180716 by Van Horn, David

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I am looking at an amplifier, which is almost a classic long tailed pair as figure 2 here: https://en.wikipedia.org/wiki/Differential_amplifier

The difference is that there is only one collector resistor, and both collectors are tied together.
What's up with that?

I haven't seen that configuration in Horowitz and Hill or Ghausi.


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2016\09\19@193210 by Spehro Pefhany

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At 06:07 PM 9/19/2016, you wrote:
>I am looking at an amplifier, which is almost a classic long tailed
>pair as figure 2 here: https://en.wikipedia.org/wiki/Differential_amplifier
>
>The difference is that there is only one collector resistor, and
>both collectors are tied together.
>What's up with that?
>
>I haven't seen that configuration in Horowitz and Hill or Ghausi.

Are you *sure* the collectors don't go to opposite ends of that one resistor?

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2016\09\19@193849 by David VanHorn

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Yup

On Sep 19, 2016 5:37 PM, "Spehro Pefhany" <speffspamKILLspaminterlog.com> wrote:

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2016\09\19@233032 by Jean-Paul Louis

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NAND gate using RTL logic?

Jean-Paul
N1JPL


{Quote hidden}

Just my $0.02,

Jean-Paul
N1JPL




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2016\09\20@002735 by David VanHorn

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It's supposed to be a differential amplifier, but I don't think it's right.

On Mon, Sep 19, 2016 at 9:30 PM, Jean-Paul Louis <@spam@louijpKILLspamspamgmail.com> wrote:

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2016\09\22@194341 by Sean Breheny

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Could it be a two-input inverting summing amplifier? It is too symmetrical
to be a differential amplifier.

On Tue, Sep 20, 2016 at 12:27 AM, David VanHorn <spamBeGonemicrobrixspamBeGonespamgmail.com> wrote:

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2016\09\23@000107 by Jean-Paul Louis

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Maybe an audio mixer. Is the collector resistor twice the emitter resistor?
I don’t recall if you gave us the resistor values.

Jean-Paul
N1JPL


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Just my $0.02,

Jean-Paul
N1JPL




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2016\09\28@100207 by Van Horn, David

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Possible.  I googled that and didn't see anything other than differentials though, with one collector tied high.
It's an odd configuration.

{Original Message removed}

2016\09\28@132448 by Jason White

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Just out of curiosity, could you post a schematic?  It might help to see it
in context.

On Wed, Sep 28, 2016 at 10:02 AM, Van Horn, David <
RemoveMEdavid.vanhornKILLspamspambackcountryaccess.com> wrote:

> Possible.  I googled that and didn't see anything other than differentials
> though, with one collector tied high.
> It's an odd configuration.
>
> {Original Message removed}

2016\09\28@175506 by Van Horn, David

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part 1 4119 bytes content-type:text/plain; charset="us-ascii" (decoded quoted-printable)

Like this

-----Original Message-----
From: piclist-bouncesSTOPspamspamspam_OUTmit.edu [spamBeGonepiclist-bouncesSTOPspamspamEraseMEmit.edu] On Behalf Of Jason White
Sent: Wednesday, September 28, 2016 11:25 AM
To: Microcontroller discussion list - Public.
Subject: Re: [EE] Long tailed pair, sort of.

Just out of curiosity, could you post a schematic?  It might help to see it in context.

On Wed, Sep 28, 2016 at 10:02 AM, Van Horn, David < KILLspamdavid.vanhornspamBeGonespambackcountryaccess.com> wrote:

{Quote hidden}

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part 2 31959 bytes content-type:image/png; name="Amp.png" (decode)


part 3 197 bytes content-type:text/plain; name="ATT00001.txt"
(decoded base64)

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2016\09\29@041704 by Richard Prosser

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Hi David,
Silly question, where is the output. TP18 ???

RP

On 29 September 2016 at 10:55, Van Horn, David
<.....david.vanhornspamRemoveMEbackcountryaccess.com> wrote:
> Like this
>
> {Original Message removed}

2016\09\29@080658 by David VanHorn

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Yes

On Sep 29, 2016 2:20 AM, "Richard Prosser" <RemoveMErhprosserspamspamBeGonegmail.com> wrote:

> Hi David,
> Silly question, where is the output. TP18 ???
>
> RP
>
> On 29 September 2016 at 10:55, Van Horn, David
> <spamBeGonedavid.vanhorn@spam@spamspam_OUTbackcountryaccess.com> wrote:
> > Like this
> >
> > {Original Message removed}

2016\09\29@090708 by alan.b.pearce

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It looks to me like it is being used as an RF mixer or modulator, considering the tuned circuit in the collector circuit.

A bit rough and crude maybe, but presumably works.



> {Original Message removed}

2016\09\29@153437 by Richard Prosser

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Yes, That was my guess.
It seems to be tuned to about 550kHz depending on strays and the load
charecteristics.  Seems a bit strange for an audio application (IIRC).
Could there be a VLF clock function involved?
Any idea as to the type & levels of the input signals?

RP

On 30 September 2016 at 02:07,  <TakeThisOuTalan.b.pearcespamspamstfc.ac.uk> wrote:
> It looks to me like it is being used as an RF mixer or modulator, considering the tuned circuit in the collector circuit.
>
> A bit rough and crude maybe, but presumably works.
>
>
>
>> {Original Message removed}

2016\09\29@163027 by Van Horn, David

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It's RF, but these days 550kHz might as well be audio-ish.  
I'm just bugged that I haven't found this configuration anywhere in Horowitz and Hill, Ghausi, or google.
Not sure what the designer was trying to do.


{Original Message removed}

2016\09\29@170629 by Jason White

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Where does the input come from? Where does the output go?

I take it this circuit is a small piece of a much larger puzzle.

On Thu, Sep 29, 2016 at 4:30 PM, Van Horn, David <
david.vanhornEraseMEspambackcountryaccess.com> wrote:

> It's RF, but these days 550kHz might as well be audio-ish.
>
> I'm just bugged that I haven't found this configuration anywhere in
> Horowitz and Hill, Ghausi, or google.
> Not sure what the designer was trying to do.
>
>
> {Original Message removed}

2016\09\29@185419 by James Cameron

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Could it be a low frequency RF transmitter for remote observation of
the audio signal?  ;-)

My TRS-80 model I level II worked that way; I used a portable AM radio
as a debugging tool.

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2016\09\29@191051 by Veronica Merryfield

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Are both inputs in use at the same time? It might be just a way to have two inputs be able to generate one output.


> On Sep 29, 2016, at 5:30 PM, Van Horn, David <RemoveMEdavid.vanhornEraseMEspamspam_OUTbackcountryaccess.com> wrote:
>
> It's RF, but these days 550kHz might as well be audio-ish.
>
> I'm just bugged that I haven't found this configuration anywhere in Horowitz and Hill, Ghausi, or google.
> Not sure what the designer was trying to do.
>
>
> {Original Message removed}

2016\09\30@000408 by Sean Breheny

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Doesn't look like a mixer to me. The only real coupling between the two
BJTs is via the collectors, which doesn't really allow one signal to affect
the gain of the other signal (i.e. multiply) unless one of the inputs is so
large that it takes both transistors into saturation and back out each
cycle of the local oscillator. But if you were doing that, there'd be no
need for the emitter degeneration or biasing network. Speaking of that,
though - the biasing network looks unnecessarily elaborate. Why is there
one common 100k resistor in the two biasing networks, with a bypass cap,
and then separate small value resistors with bypass caps? Also, why 2.8V
supply? Is there a chance that this is a bad design, such that we cannot
see the intent because it doesn't do what was intended (or only does it
slightly)?

On Thu, Sep 29, 2016 at 7:10 PM, Veronica Merryfield <
@spam@veronica.merryfieldRemoveMEspamEraseMEgmail.com> wrote:

{Quote hidden}

> > {Original Message removed}

2016\09\30@020444 by RussellMc

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Here is a functionally identical ciruit using MPF102's EXCEPT they have no
emitter/source resistor.


http://www.seekic.com/circuit_diagram/Audio_Circuit/Mixer/SIMPLE_UTILITY_MIXER.html

      Circuit diagram only
<http://www.seekic.com/uploadfile/ic-circuit/s2009795657611.gif>

Here is a RF mixer  RF + LO to IF with commoned drains BUT they use dual
gate FETs


http://www.next.gr/uploads//112/Balanced-mixer-circuit-consisting-of-two-dual-gate-field-effect-transistor-formed.png

_________________

This not quite the same arrangement separates emitter but commons
collectors - used as a colour channel separator in a mechanical TV system -
sounds like a black hole :-)
Circuit www.hawestv.com/mtv_color/colorize_images/inv_mixer.gif
>From here  <http://www.hawestv.com/mtv_color/mtv_colorize2.htm>

_________

Event Horizon - mechanical TV page - legion

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2016\09\30@102919 by Sean Breheny

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Ah, OK, an AUDIO mixer is not at all the same thing as an RF mixer (which
I'm sure you know, Russell). An audio mixer is just a summing amplifier
(which I suggested this might be much earlier in this thread). An RF mixer
is essentially a multiplier, to achieve heterodyning. It may be implemented
as a true analog multiplier (log-sum-exponentiate circuit, or Gilbert cell
over a narrow range of amplitude, or a multiplying DAC) but more often is
implemented as simply a non-linear amplifier fed by both signals or even by
diode or transistor switching circuits which just turn one of the signals
into a square wave and switch the other signal on and off in time to the
square wave, yielding not only the desired product but also various
harmonic products, too, and not responding much to small changes in the
amplitude of the LO input.

Using dual-gate FETs allows the LO to shift the operating point of the two
FETs which changes the gain of  their response to the RF input, hence
multiplying action.


On Fri, Sep 30, 2016 at 2:04 AM, RussellMc <EraseMEapptechnzspam@spam@gmail.com> wrote:

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2016\09\30@110740 by Van Horn, David

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It's supposed to be a differential amplifier, but it's like none I've ever seen.  I'm going through old notes, and I have no further information. I wish I had some text to say what the reasoning was behind this configuration. I figured one of you guys would point me to something in the literature that would be informative, but I'm going to assume that any such is either buried in the mists of time or nonexistent.
Thanks.

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2016\09\30@113554 by RussellMc

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​
On 1 October 2016 at 03:07, Van Horn, David <
@spam@david.vanhornspam_OUTspam.....backcountryaccess.com> wrote:

> It's supposed to be a differential amplifier, but it's like none I've ever
> seen.  I'm going through old notes, and I have no further information. I
> wish I had some text to say what the reasoning was behind this
> configuration.
> I figured one of you guys would point me to something in the literature
> that would be informative, but I'm going to assume that any such is either
> buried in the mists of time or nonexistent.
>
>
I'm leaning towards "non existent".
It's more like a summer, if that. Almost an analog OR function.
If both are operated at small signal relatively they sum, after a fashion.
Both operated at over half amplitude can lead to saturation.
Tuned circuit adds excitement (not in the technical sense :-) ).


  R
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'[EE] Long tailed pair, sort of.'
2016\10\01@094618 by Denny Esterline
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Assuming we're still discussing the schematic referenced via wikipedia....
I'm starting to this Occam's razor points to "mistake"

On Fri, Sep 30, 2016 at 8:35 AM, RussellMc <spamBeGoneapptechnzEraseMEspamgmail.com> wrote:

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2016\10\03@090712 by Van Horn, David

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The joys of taking over a project and looking at notes from two and three engineers ago...   :)



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2016\10\03@101554 by Jean-Paul Louis

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David, That could be a modulator, if one input receive about 500 kHz and the other side Audio signal, then the resonant circuit would select the side band. then a similar circuit with HF adjustable would make a receiver, and the whole thing become a voice distorter.

Just another $0.02,

Jean-Paul
N1JPL

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