I need to extract and amplify only the components of two signals that are exactly in phase. Out of phase signals of any amplitude are noise. I am thinking this is sort of the opposite of common mode rejection. Should I be pursuing an electronic (hardware) solution or a math (DSP) solution? Is there some way to utilize the phase part of an FFT? Ron H.
Design Question
Started by ●March 12, 2004
Reply by ●March 12, 20042004-03-12
"Ron H." wrote:> > I need to extract and amplify only the components of two signals that are > exactly in phase. Out of phase signals of any amplitude are noise. I am > thinking this is sort of the opposite of common mode rejection. Should I be > pursuing an electronic (hardware) solution or a math (DSP) solution? Is > there some way to utilize the phase part of an FFT? >Cross-Correlation
Reply by ●March 12, 20042004-03-12
On Fri, 12 Mar 2004 05:20:00 -0600, "Ron H." <ronharshbarger@mmm.com> wrote:>I need to extract and amplify only the components of two signals that are >exactly in phase. Out of phase signals of any amplitude are noise. I am >thinking this is sort of the opposite of common mode rejection. Should I be >pursuing an electronic (hardware) solution or a math (DSP) solution? Is >there some way to utilize the phase part of an FFT?Take a look at quadrature demodulation - in either hardware or software. It is perfectly suited to extracting the in-phase component of a signal as well as the 90-degrees out-of-phase component. -Robert Scott Ypsilanti, Michigan (Reply through this forum, not by direct e-mail to me, as automatic reply address is fake.)
Reply by ●March 12, 20042004-03-12
"Ron H." <ronharshbarger@mmm.com> wrote in message news:c2s6d0$9ki$1@tuvok3.mmm.com...> I need to extract and amplify only the components of two signals that are > exactly in phase. Out of phase signals of any amplitude are noise. I am > thinking this is sort of the opposite of common mode rejection. Should Ibe> pursuing an electronic (hardware) solution or a math (DSP) solution? Is > there some way to utilize the phase part of an FFT?If E(total) = E(common mode) + E(non-common mode) and a common mode circuit yields E(non-common mode) then E(common mode) = E(total) - E(non-common mode) so you can run the signal through a common mode rejection circuit ( Do a Google search on "quadrature rejection" ), subtract the resultant signal from the original signal, and then amplify the resultant. Of course, the best way to separate signal from noise, is to cross-correlate the "effect" signal with the "cause" signal. A Google search on MTI RADAR might show you how auto-correlation is done with analog circuits. Correlation involves summing the product of two strings of data. If you multiply two random strings of data, and sum the products, you end up with zero in the case of pure noise. The larger the sum of the products, the greater the correlation between the two strings. Note that the time delay (Phase in the case of periodic signals) has to be adjusted to make the data strings overlap, as there is a time interval or phase difference between a cause and an effect. -- Tom Potter http://tompotter.us
Reply by ●March 12, 20042004-03-12
"Ron H." <ronharshbarger@mmm.com> wrote in message news:c2s6d0$9ki$1@tuvok3.mmm.com...> I need to extract and amplify only the components of two signalsthat are> exactly in phase. Out of phase signals of any amplitude are noise. Iam> thinking this is sort of the opposite of common mode rejection.Should I be> pursuing an electronic (hardware) solution or a math (DSP) solution?Is> there some way to utilize the phase part of an FFT? > > Ron H. > > >Google on "lock in amplifier" (without the quotes). Regards Ian
Reply by ●March 12, 20042004-03-12
Ian Buckner wrote:> "Ron H." <ronharshbarger@mmm.com> wrote in message > news:c2s6d0$9ki$1@tuvok3.mmm.com... > >>I need to extract and amplify only the components of two signals > > that are > >>exactly in phase. Out of phase signals of any amplitude are noise. I > > am > >>thinking this is sort of the opposite of common mode rejection. > > Should I be > >>pursuing an electronic (hardware) solution or a math (DSP) solution? > > Is > >>there some way to utilize the phase part of an FFT? >> >>Ron H. >> >> >> > > > Google on "lock in amplifier" (without the quotes). > > Regards > Ian >Actually I think the result with quotes is better. Three of the first four hits are just what you're looking for. IMHO
Reply by ●March 12, 20042004-03-12
In article <c2s6d0$9ki$1@tuvok3.mmm.com>, Ron H. <ronharshbarger@mmm.com> wrote:>I need to extract and amplify only the components of two signals that are >exactly in phase. Out of phase signals of any amplitude are noise. I am >thinking this is sort of the opposite of common mode rejection. Should I be >pursuing an electronic (hardware) solution or a math (DSP) solution? Is >there some way to utilize the phase part of an FFT? > >Ron H.Isn't that what a lock-in amplifier does? It can pick out a signal that's swamped by orders of magnitude more noise. -- "We don't grow up hearing stories around the camp fire anymore about cultural figures. Instead we get them from books, TV or movies, so the characters that today provide us a common language are corporate creatures" -- Rebecca Tushnet
Reply by ●March 12, 20042004-03-12
"Ron H." <ronharshbarger@mmm.com> wrote in message news:<c2s6d0$9ki$1@tuvok3.mmm.com>...> I need to extract and amplify only the components of two signals that are > exactly in phase. Out of phase signals of any amplitude are noise. I am > thinking this is sort of the opposite of common mode rejection. Should I be > pursuing an electronic (hardware) solution or a math (DSP) solution? Is > there some way to utilize the phase part of an FFT? >Phase Locked Loop (PLL)?> Ron H.
Reply by ●March 12, 20042004-03-12
Noise may exist or not exist. You also need an oscilloscope to engineer this. Keep the signals separate and simply amplify. If you want to compare the signals, then the fact they are in phase won't produce cancellation. Common mode rejection occurs because the signals are identical, basically.
Reply by ●March 12, 20042004-03-12
Ian Buckner wrote:> "Ron H." <ronharshbarger@mmm.com> wrote in message > news:c2s6d0$9ki$1@tuvok3.mmm.com... > >>I need to extract and amplify only the components of two signals > > that are > >>exactly in phase. Out of phase signals of any amplitude are noise. I > > am > >>thinking this is sort of the opposite of common mode rejection. > > Should I be > >>pursuing an electronic (hardware) solution or a math (DSP) solution? > > Is > >>there some way to utilize the phase part of an FFT? >> >>Ron H. >> >> >> > > > Google on "lock in amplifier" (without the quotes). > > Regards > Ian"lock in amplifier" or "lock-in amplifier" with quotes is even better. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
