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zahrein
Joined: 28 May 2004
Posts: 144
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 06 Oct 2004 4:51 The advantage of differential apmplifier mode? |
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Guyz,
What is the advantage of differential amplifier?
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Neo_82
Joined: 29 Apr 2004
Posts: 37
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| 06 Oct 2004 5:18 Re: The advantage of differential apmplifier mode? |
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if you are talkin about diferencial input and single output, we can say that this king of amplifiers help to reject common mode input, i mean it help to increse CMRR, besides those amplifiers increse SNR (signal to noise ratio) at the input of one Opamp. A fully diferential apamp provides a larger output voltage swing and are less susceptiblr to common mode noise.
you can find more information at Gray`s book chpters 6 and 12
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radiohead
Joined: 13 May 2004
Posts: 331
Helped: 22
Location: Heart of Europe
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| 06 Oct 2004 7:51 Re: The advantage of differential apmplifier mode? |
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| a high CMRR is good because it defines the difference at the output of an amplified differential mode input to an amplifier common mode input. Unwanted signals that couple into the differential input, predominantly will result in an unwanted common mode signal at the input. The high CMRR blocks this from further propagation!
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samcheetah
Joined: 25 May 2004
Posts: 672
Helped: 31
Location: Pakistan
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| 06 Oct 2004 13:27 Re: The advantage of differential apmplifier mode? |
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well if u are talking about full differential opamps which have differential input and differential output then there are a couple of advantages of them in comparison with opamps with single ended output.
the newer high speed A/D converters require differential inputs. for that u must have a fully differential opamp. if u have a single ended output opamp then u will have to use a transformer to connect the amp to the A/D converter (i dont know the configuration). there are a number of other advantages of fully differential opamps over single ended output opamps.
see the SLOA064 application note at TI's website. for a collection of differential opamp circuits
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djalli
Joined: 10 Nov 2001
Posts: 887
Helped: 15
Location: 1600 Pennsylvania Avenue, Washington DC 20500
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| 07 Oct 2004 12:44 Re: The advantage of differential apmplifier mode? |
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| zahrein wrote: |
Guyz,
What is the advantage of differential amplifier? |
First! The differential amplification come from the input emitter-coupled pair or source-coupled in an transistor amplifier.
In opamps advantage is because of what I said you achieve exellent CMRR.
In opamps companies do either by source-coupled pair or emitter-coupled pair. The ones to achieve exellent CMRR are the ones with the input emitter-coupled pair.
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mopengfei
Joined: 10 Aug 2004
Posts: 41
Location: hangzhou of china
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| 08 Oct 2004 2:06 The advantage of differential apmplifier mode? |
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in summary, this kind of amplifier increse CMRR,
increse SNR compared to onther amplifer
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ramgopal
Joined: 24 Sep 2004
Posts: 5
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| 08 Oct 2004 3:42 Re: The advantage of differential apmplifier mode? |
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In layman's term it amplifies the difference between 2 input signal rather than there absolute values
Vinp1 = Vcm + Vdif/2
Vinp2 = Vcm - Vdif/2
Vout = A ( Vinp1- Vinp2) = A(Vdiff)
Independent of the common mode signal Vcm. In reality you have a small gain for the common mode signal .....hence the term CMRR.
regards
Ramgopal
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khafaji
Joined: 28 Sep 2004
Posts: 19
Helped: 1
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| 08 Oct 2004 11:33 The advantage of differential apmplifier mode? |
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| Because the nonlinearity of transistors you can see any harmonic of input in the response of single transistor amplifier but in the differential amplifier you see only odd harmonics and this mean increase in S/N ratio
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tavakoli
Joined: 31 Dec 2003
Posts: 69
Helped: 1
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| 08 Oct 2004 12:34 Re: The advantage of differential apmplifier mode? |
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about diif amplifires this kind of amplifiers are best choice for building an wide band amps coz they don't need ac coupling at all an we can fully supporate DC and AC analyses with out taking care off DC level in AC analyses so we dont need coupling capacitors so it works in wide renge of freq and also it has other adventages as being a diff amp we could minimize a line noise like what we do in USB (has a diff signal) .....
but it is important that this kind of amp could only used when we have a large value of CMRR .......
if u need more info tell .....
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