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Monday Afternoon Exercise for the Student

Monday Afternoon Exercise for the Student...

Newsgroups: alt.binaries.schematics.electronic Subject: WhatZit? - WhatZit.pdf Message-ID:

WhatZit?

That is, what does it do?

VDD=2V

...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 | |

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| 1962 | America: Land of the Free, Because of the Brave

Reply to
Jim Thompson
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Well-without going into a lot of detail over W/L ratios, mobilities for n- and p- type materials and Cox's, the drain IDC's for MN1 and MN2 force their VGS's to be the same, insofar as the process achieves sameness, then the common source MP1 must source a current of (Vin1-VGS)/2M into the source ckt of MN1. MP2 mirrors this into the source ckt of MN2 developing Vin1-VGS across R3. So then Vin2=VGS+ Vin1-VGS + I,MP3*2M , making I,MP3=(Vin2-Vin1)/2M, which is mirrored by MP4 and developed across R2, so Vout=Vin2-Vin1. It is a differential to single ended converter with unity gain.

Reply to
Fred Bloggs

Yep. From an RFID tag.

...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     |
             
         America: Land of the Free, Because of the Brave
Reply to
Jim Thompson

Sure you can. You correctly deduced all the matching, so the answer is ratiometric.

(VDD=2 was only mentioned to keep the smart-asses amongst us from saying, Why didn't you just use a diff-pair or an OpAmp?")

...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     |
             
         America: Land of the Free, Because of the Brave
Reply to
Jim Thompson

Nothing, if Vg(thresh) is less than Vdd. :P

Let's see, MN1 amplifies IN1. The drain load I1 and MP1 inverts drain current, causing NFB to MN1 source, linearizing it. MP2, if matched to MP1, reproduces the current, feeding the same error signal to MN2's source. (Similarly, MP4 causes a voltage/current at OUT equal to MP3's current.) Since MP2 causes a current into MN2's source, it develops voltage which subtracts from IN2.

Therefore, it is a MOS differential amplifier.

I don't know the significance of Vdd = 2 and I don't know the characteristics of the MOS, so I can't perform any calculations.

Tim

-- Deep Fryer: A very philosophical monk. Website @

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Reply to
Tim Williams

Ah, I suppose so- the gates cancel out, huh? The currents and resistors keep it straightforward. BTW, aren't IC resistors nasty, or has process improved them since?

I wouldn't have guessed the gain as unity, but then, given the source resistors, those will degenerate it just right.

Tim

-- Deep Fryer: A very philosophical monk. Website @

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Reply to
Tim Williams

Eh?

Aren't you the one who just applauded Lionel with, "Words of a wise, wise man."??

You don't have a clue how the circuit works. It has no "gates"... it's analog.

...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     |
             
         America: Land of the Free, Because of the Brave
Reply to
Jim Thompson

Well? Be "more exact" and I won't be "reactionary" ;-)

They are *current mirrors* actually.

And the accuracy is developed using an NMOS/PMOS combination quite like what has been bandied about in bipolar (NPN/PNP) with the mike preamp.

...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     |
             
         America: Land of the Free, Because of the Brave
Reply to
Jim Thompson

Um..grids? No, that's tubes...

I meant gate-source voltage, to be more exact.

You're just being reactionary to a post of mine elsewhere.

Tim

-- Deep Fryer: A very philosophical monk. Website @

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Reply to
Tim Williams

I don't read threads more than 25% PA and MP, so I haven't been watching that thread.

Tim

-- Deep Fryer: A very philosophical monk. Website @

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Reply to
Tim Williams

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