Differential-pair amplifer

R

Reg Edwards

Guest
If it is true that a pair of transistors, a differential pair
amplifier, has a Tanh transfer characteristic, then at audio
frequencies it behaves as a sort of amplitide or volume compandor.

At large signal inputs the output approaches a squarewaveform and
hopeless distortion occurs. At intermediate inputs audio distortion
increasingly appears.

What other so-called useful applications does the circuit have? I
can't think of any myself?
----
Reg.
 
"Reg Edwards" <g4fgq.regp@ZZZbtinternet.com> wrote in message
news:d65nb5$pqs$2@nwrdmz03.dmz.ncs.ea.ibs-infra.bt.com...
If it is true that a pair of transistors, a differential pair
amplifier, has a Tanh transfer characteristic, then at audio
frequencies it behaves as a sort of amplitide or volume compandor.

At large signal inputs the output approaches a squarewaveform and
hopeless distortion occurs. At intermediate inputs audio distortion
increasingly appears.

What other so-called useful applications does the circuit have? I
can't think of any myself?
----
Reg.
Click to expand...
you can convert a triangle wave to a pretty good aproximation of a sinewave
with it.

Colin =^.^=
 
colin wrote:
"Reg Edwards" <g4fgq.regp@ZZZbtinternet.com> wrote in message
news:d65nb5$pqs$2@nwrdmz03.dmz.ncs.ea.ibs-infra.bt.com...
(snip)
Click to expand...

What other so-called useful applications does the circuit have? I
can't think of any myself?

you can convert a triangle wave to a pretty good aproximation of a sinewave
with it.
Click to expand...
Two properly adjusted stages can produce a damn good approximation of
a sine wave from a triangle.
 
Reg Edwards wrote:
If it is true that a pair of transistors, a differential pair
amplifier, has a Tanh transfer characteristic,
Click to expand...
That is my understanding.

then at audio
frequencies it behaves as a sort of amplitide or volume compandor.
Click to expand...
Well, the compressor part of the compander, anyway. You need another
one in a feedback path to do the equivalent expanding, downstream.

At large signal inputs the output approaches a squarewaveform and
hopeless distortion occurs. At intermediate inputs audio distortion
increasingly appears.

What other so-called useful applications does the circuit have? I
can't think of any myself?
Click to expand...
I think it is useful to compress a wide range AC signal to be
digitized by an A/D converter, having high resolution at small
amplitudes, and lower resolution for large amplitudes, where the
resolution is mostly wasted the A/D result can then be linearized with
a look up table.

I think audio that any exceed the swing limits of a power amplifier
sounds a lot better if the hard clipping is prevented by predistorting
the audio with a tanh compressor so that the power stage cannot reach
clipping level, or if it does, clips gently, so it doesn't generate
such high harmonics of the signal frequencies.
 
On Sat, 14 May 2005 20:33:41 +0000 (UTC), "Reg Edwards"
<g4fgq.regp@ZZZbtinternet.com> wrote:

If it is true that a pair of transistors, a differential pair
amplifier, has a Tanh transfer characteristic, then at audio
frequencies it behaves as a sort of amplitide or volume compandor.

At large signal inputs the output approaches a squarewaveform and
hopeless distortion occurs. At intermediate inputs audio distortion
increasingly appears.

What other so-called useful applications does the circuit have? I
can't think of any myself?
Click to expand...

As you observe, differential pairs are totally worthless. Nobody uses
them any more.


John
 
On Sat, 14 May 2005 16:10:59 -0700, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Sat, 14 May 2005 20:33:41 +0000 (UTC), "Reg Edwards"
g4fgq.regp@ZZZbtinternet.com> wrote:

If it is true that a pair of transistors, a differential pair
amplifier, has a Tanh transfer characteristic, then at audio
frequencies it behaves as a sort of amplitide or volume compandor.

At large signal inputs the output approaches a squarewaveform and
hopeless distortion occurs. At intermediate inputs audio distortion
increasingly appears.

What other so-called useful applications does the circuit have? I
can't think of any myself?


As you observe, differential pairs are totally worthless. Nobody uses
them any more.


John
Click to expand...
ROTFLMAO! Dummies are good for business... except when they insist
they know what they are doing :-(

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.
 
In article <d65nb5$pqs$2@nwrdmz03.dmz.ncs.ea.ibs-infra.bt.com>,
Reg Edwards <g4fgq,regp@ZZZbtinternet,com> wrote:
[...]
At large signal inputs the output approaches a squarewaveform and
hopeless distortion occurs.
Click to expand...
That distortion is not hopeless if it is what you need. In that case it
is very nice distortion. Take a look at the circuit of a comparitor IC
like the LM339. It distorts like crazy just like you would want it to.


What other so-called useful applications does the circuit have? I
can't think of any myself?
Click to expand...
If you combine a few in tricky ways, you can make an analog multiplier and
or, a circuit that finds the RMS of an applied waveform.

You can use them to perform logical operations.


--
--
kensmith@rahul.net forging knowledge
 
In article <d65nb5$pqs$2@nwrdmz03.dmz.ncs.ea.ibs-infra.bt.com>,
g4fgq.regp@ZZZbtinternet.com says...
What other so-called useful applications does the circuit have?
I can't think of any myself?
Click to expand...
I guess you don't consider a circuit whose output is a
function of the difference between two inputs useful,
but a lot of op-amp makers find it convenient...
 
John Larkin wrote:
On Sat, 14 May 2005 20:33:41 +0000 (UTC), "Reg Edwards"
g4fgq.regp@ZZZbtinternet.com> wrote:

If it is true that a pair of transistors, a differential pair
amplifier, has a Tanh transfer characteristic, then at audio
frequencies it behaves as a sort of amplitide or volume compandor.

At large signal inputs the output approaches a squarewaveform and
hopeless distortion occurs. At intermediate inputs audio distortion
increasingly appears.

What other so-called useful applications does the circuit have? I
can't think of any myself?


As you observe, differential pairs are totally worthless. Nobody uses
them any more.
Click to expand...
Not at all. You just need to know how to design with them correctly:)

http://www.anasoft.co.uk/EE/MicAmpDesign/MicAmpDesign.html

If you want really high CMRR, they are the *only* way to go. And as we
can see from the above, in the correct configuration, distortion can be
very low indeed.

Kevin Aylward
informationEXTRACT@anasoft.co.uk
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.
 
On Sat, 14 May 2005 20:33:41 +0000 (UTC), in sci.electronics.design
"Reg Edwards" <g4fgq.regp@ZZZbtinternet.com> wrote:

If it is true that a pair of transistors, a differential pair
amplifier, has a Tanh transfer characteristic, then at audio
frequencies it behaves as a sort of amplitide or volume compandor.

At large signal inputs the output approaches a squarewaveform and
hopeless distortion occurs. At intermediate inputs audio distortion
increasingly appears.

What other so-called useful applications does the circuit have? I
can't think of any myself?
----
Reg.

It s useful in analogue video when you are doing cross mix between 2
Click to expand...
video source ISTR, (from a video servicing course at Ampex years ago)
Sorry Reg, I cant remember the theory, I fell asleep during this part
of the course


martin

After the first death, there is no other.
(Dylan Thomas)
 
Kevin Aylward wrote...
John Larkin wrote:
Reg Edwards wrote:

If it is true that a pair of transistors, a differential pair
amplifier, has a Tanh transfer characteristic, then at audio
frequencies it behaves as a sort of amplitide or volume compandor.

At large signal inputs the output approaches a squarewaveform and
hopeless distortion occurs. At intermediate inputs audio distortion
increasingly appears.

What other so-called useful applications does the circuit have?
I can't think of any myself?

As you observe, differential pairs are totally worthless. Nobody
uses them any more.

Not at all. You just need to know how to design with them correctly:)
Click to expand...
Kevin, Kevin... John was merely speaking tongue-in-cheek!


--
Thanks,
- Win
 
Winfield Hill wrote:
Kevin Aylward wrote...
John Larkin wrote:
Reg Edwards wrote:

If it is true that a pair of transistors, a differential pair
amplifier, has a Tanh transfer characteristic, then at audio
frequencies it behaves as a sort of amplitide or volume compandor.

At large signal inputs the output approaches a squarewaveform and
hopeless distortion occurs. At intermediate inputs audio distortion
increasingly appears.

What other so-called useful applications does the circuit have?
I can't think of any myself?

As you observe, differential pairs are totally worthless. Nobody
uses them any more.

Not at all. You just need to know how to design with them
correctly:)

Kevin, Kevin... John was merely speaking tongue-in-cheek!
Click to expand...
Indeed. But we don't want any newbies to get the wrong idea:)

Tell you what though, this discrete design lark is getting really
difficult. All the components are disappearing. Its really hard to find
*small* signal mosfets. They are all 1A high Cgs jobs. So far, I'm back
to the 25+ year old SD211 for its low capacitance as a part of a current
source. Still looking for a pmos with a spice model. I get lazy now, I
found one pmos, but cant be bothered to make the model as one wasn't
given.

Kevin Aylward
informationEXTRACT@anasoft.co.uk
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.
 
Kevin Aylward wrote...
Tell you what though, this discrete design lark is getting really
difficult. All the components are disappearing. Its really hard to find
*small* signal mosfets. They are all 1A high Cgs jobs. So far, I'm back
to the 25+ year old SD211 for its low capacitance as a part of a current
source. Still looking for a pmos with a spice model. I get lazy now,
I found one pmos, but cant be bothered to make the model as one wasn't
given.
Click to expand...
Now Kevin, I'm slaving away making accurate low-current MOSFET
spice models, you can join the fray, too. The more the merrier.
Also, just because a MOSFET model is available, don't assume it's
accurate below say 3 to 5% of the FET's absolute-maximum current.
In other words, it's likely to be inaccurate in the subthreshold
linear-circuit region that interests us. However, it's not too
hard to fix the models with a current-controlled current source
feeding a diode directly in series with the FET's gate. Using n=3
works pretty good for a 2n7000, big power MOSFETs are around n=5.

See the Steven M. Sandler and Charles E. Hymowitz article in the
May 2005 issue of Power Electronics Technology magazine. OK,
I know it's not out yet, but... In the meantime, try this link,
http://www.edacafe.com/technical/papers/Mosfet_paper.php

Sandler's approach works well, after correcting his parameters.


--
Thanks,
- Win
 
Reg Edwards wrote:
If it is true that a pair of transistors, a differential pair
amplifier, has a Tanh transfer characteristic, then at audio
frequencies it behaves as a sort of amplitide or volume compandor.

At large signal inputs the output approaches a squarewaveform and
hopeless distortion occurs. At intermediate inputs audio distortion
increasingly appears.
Click to expand...
Hello- ever hear of something called feedback- can be used to
pre-distort the input drive of the diff amp as well as maintain
operation in small signal region. Is there such a thing as a monolithic
op amp without a differential amplifier front-end?
 
On 15 May 2005 04:59:44 -0700, Winfield Hill
<hill_a@t_rowland-dotties-harvard-dot.s-edu> wrote:

Kevin Aylward wrote...

Tell you what though, this discrete design lark is getting really
difficult. All the components are disappearing. Its really hard to find
*small* signal mosfets. They are all 1A high Cgs jobs. So far, I'm back
to the 25+ year old SD211 for its low capacitance as a part of a current
source. Still looking for a pmos with a spice model. I get lazy now,
I found one pmos, but cant be bothered to make the model as one wasn't
given.

Now Kevin, I'm slaving away making accurate low-current MOSFET
spice models, you can join the fray, too. The more the merrier.
Also, just because a MOSFET model is available, don't assume it's
accurate below say 3 to 5% of the FET's absolute-maximum current.
In other words, it's likely to be inaccurate in the subthreshold
linear-circuit region that interests us. However, it's not too
hard to fix the models with a current-controlled current source
feeding a diode directly in series with the FET's gate. Using n=3
works pretty good for a 2n7000, big power MOSFETs are around n=5.

See the Steven M. Sandler and Charles E. Hymowitz article in the
May 2005 issue of Power Electronics Technology magazine. OK,
I know it's not out yet, but... In the meantime, try this link,
http://www.edacafe.com/technical/papers/Mosfet_paper.php

Sandler's approach works well, after correcting his parameters.
Click to expand...
What? You don't want to deal directly with the device model ?:)

As I showed a while back, the Supertex Level=3 model was pretty close,
without adding on subcircuit elements.

I'm always leery of add-ons based on limited measured data, covers one
particular case, but may bomb out on the next.

How does this model behave in regard to modeling gate charge?

Win, I don't receive PET magazine. Could you get me a copy of the
Sandler & Hymowitz article when it comes out? Thanks!

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.
 
On Sun, 15 May 2005 13:24:38 GMT, Fred Bloggs <nospam@nospam.com>
wrote:

Reg Edwards wrote:
If it is true that a pair of transistors, a differential pair
amplifier, has a Tanh transfer characteristic, then at audio
frequencies it behaves as a sort of amplitide or volume compandor.

At large signal inputs the output approaches a squarewaveform and
hopeless distortion occurs. At intermediate inputs audio distortion
increasingly appears.

Hello- ever hear of something called feedback- can be used to
pre-distort the input drive of the diff amp as well as maintain
operation in small signal region. Is there such a thing as a monolithic
op amp without a differential amplifier front-end?
Click to expand...
Current-mode opamps have a different topology.

John
 
John Larkin wrote:
On Sun, 15 May 2005 13:24:38 GMT, Fred Bloggs <nospam@nospam.com
wrote:



Reg Edwards wrote:

If it is true that a pair of transistors, a differential pair
amplifier, has a Tanh transfer characteristic, then at audio
frequencies it behaves as a sort of amplitide or volume compandor.

At large signal inputs the output approaches a squarewaveform and
hopeless distortion occurs. At intermediate inputs audio distortion
increasingly appears.

Hello- ever hear of something called feedback- can be used to
pre-distort the input drive of the diff amp as well as maintain
operation in small signal region. Is there such a thing as a monolithic
op amp without a differential amplifier front-end?


Current-mode opamps have a different topology.

John
Click to expand...
Most people understand op amp to mean voltage mode- current mode only
made a difference because people were too lazy to invent a different
circuit symbol.
 
On Sun, 15 May 2005 21:07:55 GMT, Fred Bloggs <nospam@nospam.com>
wrote:

John Larkin wrote:
On Sun, 15 May 2005 13:24:38 GMT, Fred Bloggs <nospam@nospam.com
wrote:



Reg Edwards wrote:

If it is true that a pair of transistors, a differential pair
amplifier, has a Tanh transfer characteristic, then at audio
frequencies it behaves as a sort of amplitide or volume compandor.

At large signal inputs the output approaches a squarewaveform and
hopeless distortion occurs. At intermediate inputs audio distortion
increasingly appears.

Hello- ever hear of something called feedback- can be used to
pre-distort the input drive of the diff amp as well as maintain
operation in small signal region. Is there such a thing as a monolithic
op amp without a differential amplifier front-end?


Current-mode opamps have a different topology.

John


Most people understand op amp to mean voltage mode- current mode only
made a difference because people were too lazy to invent a different
circuit symbol.
Click to expand...

You'd better explain that to all the semiconductor companies; they
keep calling them 'opamps'.

John
 
On 15 May 2005 19:52:28 -0700, Winfield Hill
<hill_a@t_rowland-dotties-harvard-dot.s-edu> wrote:

Jim Thompson wrote...

See the Steven M. Sandler and Charles E. Hymowitz article in the
May 2005 issue of Power Electronics Technology magazine. OK,
I know it's not out yet, but... In the meantime, try this link,
http://www.edacafe.com/technical/papers/Mosfet_paper.php

Sandler's approach works well, after correcting his parameters.

What? You don't want to deal directly with the device model ?:)

As I showed a while back, the Supertex Level=3 model was pretty
close, without adding on subcircuit elements.

Where'd you show that? I'd love to take a look at it.

Bring it on.

[snip]
Click to expand...

Originally posted to A.B.S.E on 4/6/2005, re-posted at....

Newsgroups: alt.binaries.schematics.electronic
Subject: Win Hill - 2N7000 Spice Model Comparisons -
Compare2N7000Models.pdf
Message-ID: <iqbh81l24r4vilqrg4qsigekl0pargd1rk@4ax.com>

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.
 
mike wrote...
Win wrote:

See the Steven M. Sandler and Charles E. Hymowitz article in the
May 2005 issue of Power Electronics Technology magazine. OK, I
know it's not out yet, but... In the meantime, try this link,
http://www.edacafe.com/technic al/papers/Mosfet_paper.php

Sandler's approach works well, after correcting his parameters.

The article just showed up on PET. It is in two parts. The
first part is

SPICE Model Supports LDO Regulator Designs May 1, 2005
By Steven Sandler, Program Engineer, Acme Electric, Tempe, Ariz.
http://powerelectronics.com/mag/power_spice_model_supports/

The second part is
SPICE Model Supports LDO Regulator Design
Continuation of Article in Power Electronics Technology May 2005
By Steven M. Sandler and Charles E. Hymowitz
http://www.aeng.com/Articles/MosFet.asp
Click to expand...
Thanks, that's it. I found Sandler's technique easy to use, and
it worked better than a similar method I had developed (out of
desperation) using three to five series transistors.


--
Thanks,
- Win
 
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