Synchrounous signal extraction technique name

S

Steven K. Moore

Guest
In my line of work, we extract the magnitude and phase of a response signal
when the excitation signal is known. The excitation is of the form
A*sin(wt) and the response is of the form B*sin(wt+theta) + noise. The
response is sampled 16 times over a full period. Let's denote the sampled
response as R[0] through R[15]. Then the inphase (real) and quadrature
(imag) components are extracted by:

real = sum(i=0 to 15) of [R*cos(2*pi()*i/16)]
imag = sum(i=0 to 15) of [R*sin(2*pi()*i/16)]

From this the magnitude and phase of the response signal is determined.

My question is what is this technique called? I'm sure there is a common
name for it. Some of my colleagues refer to it as a DFT (Discrete Fourier
Transform). Since only a single frequency component is being extracted, I
don't feel this is proper nomenclature. I'm looking for a more correct term
to use to refer to this single frequency extraction technique. Does anyone
have a good name for this?

Thanks,
--
Steve Moore
Steve.Moore@IEEE.org
 
On Fri, 27 May 2005 23:14:28 GMT, "Steven K. Moore" <smoore2@indy.rr.com> wroth:

My question is what is this technique called? I'm sure there is a common
name for it.

Thanks,
Click to expand...
How does that technique differ from the traditional "lock-in amplifier"?

Jim
 
This is sampled first and numerically processed (aka DSP). I think of the
lock-in amp approach as analog I & Q multipliers and lowpass filters to
obtain real and imag components.


"James Meyer" <jmeyer@nowhere.net> wrote in message
news:2ucf91hr8nk6l9ck5rj1siif84napb2n7b@4ax.com...
On Fri, 27 May 2005 23:14:28 GMT, "Steven K. Moore" <smoore2@indy.rr.com
wroth:


My question is what is this technique called? I'm sure there is a common
name for it.

Thanks,

How does that technique differ from the traditional "lock-in amplifier"?

Jim
Click to expand...
 
Steven K. Moore wrote:
In my line of work, we extract the magnitude and phase of a response signal
when the excitation signal is known. The excitation is of the form
A*sin(wt) and the response is of the form B*sin(wt+theta) + noise. The
response is sampled 16 times over a full period. Let's denote the sampled
response as R[0] through R[15]. Then the inphase (real) and quadrature
(imag) components are extracted by:

real = sum(i=0 to 15) of [R*cos(2*pi()*i/16)]
imag = sum(i=0 to 15) of [R*sin(2*pi()*i/16)]

From this the magnitude and phase of the response signal is determined.

My question is what is this technique called? I'm sure there is a common
name for it. Some of my colleagues refer to it as a DFT (Discrete Fourier
Transform). Since only a single frequency component is being extracted, I
don't feel this is proper nomenclature. I'm looking for a more correct term
to use to refer to this single frequency extraction technique. Does anyone
have a good name for this?

Thanks,
Click to expand...

Your computation is the very definition of DFT evaluated at Fs/16,
Fs=sampling frequency =w =2*pi*Fs/16 in the case. DFT is a function that
evaluates at 0, Fs/16, 2*Fs/16,..., 15*Fs/16. So you could term this
"DFT evaluated at the resolution frequency."
 
Steven K. Moore wrote:

In my line of work, we extract the magnitude and phase of a response signal
when the excitation signal is known. The excitation is of the form
A*sin(wt) and the response is of the form B*sin(wt+theta) + noise. The
response is sampled 16 times over a full period. Let's denote the sampled
response as R[0] through R[15]. Then the inphase (real) and quadrature
(imag) components are extracted by:

real = sum(i=0 to 15) of [R*cos(2*pi()*i/16)]
imag = sum(i=0 to 15) of [R*sin(2*pi()*i/16)]

From this the magnitude and phase of the response signal is determined.

My question is what is this technique called? I'm sure there is a common
name for it. Some of my colleagues refer to it as a DFT (Discrete Fourier
Transform). Since only a single frequency component is being extracted, I
don't feel this is proper nomenclature. I'm looking for a more correct term
to use to refer to this single frequency extraction technique. Does anyone
have a good name for this?

Thanks,
Click to expand...

I call it I/Q demodulation. Yes, it is a single-frequency DFT as well,
but thats a pretty fancy name for a pretty simple operation.

--
-------------------------------------------
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
 
Tim Wescott wrote:
Steven K. Moore wrote:

In my line of work, we extract the magnitude and phase of a response
signal when the excitation signal is known. The excitation is of the
form A*sin(wt) and the response is of the form B*sin(wt+theta) +
noise. The response is sampled 16 times over a full period. Let's
denote the sampled response as R[0] through R[15]. Then the inphase
(real) and quadrature (imag) components are extracted by:

real = sum(i=0 to 15) of [R*cos(2*pi()*i/16)]
imag = sum(i=0 to 15) of [R*sin(2*pi()*i/16)]

From this the magnitude and phase of the response signal is determined.

My question is what is this technique called? I'm sure there is a
common name for it. Some of my colleagues refer to it as a DFT
(Discrete Fourier Transform). Since only a single frequency component
is being extracted, I don't feel this is proper nomenclature. I'm
looking for a more correct term to use to refer to this single
frequency extraction technique. Does anyone have a good name for this?

Thanks,


I call it I/Q demodulation. Yes, it is a single-frequency DFT as well,
but thats a pretty fancy name for a pretty simple operation.
Click to expand...

Nah- it's called "coherent detection" generally because there is
coherence between his sampling frequency and the signal frequency.
 
Fred Bloggs wrote:
Tim Wescott wrote:

Steven K. Moore wrote:

In my line of work, we extract the magnitude and phase of a response
signal when the excitation signal is known. The excitation is of the
form A*sin(wt) and the response is of the form B*sin(wt+theta) +
noise. The response is sampled 16 times over a full period. Let's
denote the sampled response as R[0] through R[15]. Then the inphase
(real) and quadrature (imag) components are extracted by:

real = sum(i=0 to 15) of [R*cos(2*pi()*i/16)]
imag = sum(i=0 to 15) of [R*sin(2*pi()*i/16)]

From this the magnitude and phase of the response signal is determined.

My question is what is this technique called? I'm sure there is a
common name for it. Some of my colleagues refer to it as a DFT
(Discrete Fourier Transform). Since only a single frequency
component is being extracted, I don't feel this is proper
nomenclature. I'm looking for a more correct term to use to refer to
this single frequency extraction technique. Does anyone have a good
name for this?

Thanks,



I call it I/Q demodulation. Yes, it is a single-frequency DFT as
well, but thats a pretty fancy name for a pretty simple operation.


Nah- it's called "coherent detection" generally because there is
coherence between his sampling frequency and the signal frequency.

I've seen it called any number of things, including things not even
Click to expand...

repeatable here. So we probably have licence to call it pretty much
anything we want. How about if I call it "Fred Bloggs" from now on, and
you call it "Tim Wescott".

--
-------------------------------------------
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
 
Tim Wescott wrote:
Fred Bloggs wrote:



Tim Wescott wrote:

Steven K. Moore wrote:

In my line of work, we extract the magnitude and phase of a response
signal when the excitation signal is known. The excitation is of
the form A*sin(wt) and the response is of the form B*sin(wt+theta) +
noise. The response is sampled 16 times over a full period. Let's
denote the sampled response as R[0] through R[15]. Then the inphase
(real) and quadrature (imag) components are extracted by:

real = sum(i=0 to 15) of [R*cos(2*pi()*i/16)]
imag = sum(i=0 to 15) of [R*sin(2*pi()*i/16)]

From this the magnitude and phase of the response signal is determined.

My question is what is this technique called? I'm sure there is a
common name for it. Some of my colleagues refer to it as a DFT
(Discrete Fourier Transform). Since only a single frequency
component is being extracted, I don't feel this is proper
nomenclature. I'm looking for a more correct term to use to refer
to this single frequency extraction technique. Does anyone have a
good name for this?

Thanks,




I call it I/Q demodulation. Yes, it is a single-frequency DFT as
well, but thats a pretty fancy name for a pretty simple operation.


Nah- it's called "coherent detection" generally because there is
coherence between his sampling frequency and the signal frequency.

I've seen it called any number of things, including things not even
repeatable here. So we probably have licence to call it pretty much
anything we want. How about if I call it "Fred Bloggs" from now on, and
you call it "Tim Wescott".
Click to expand...

Thats just silly. Use "Tim Bloggs" and "Fred Wescott".

Cheers
DaFTerry
 
Tim Wescott wrote:
Fred Bloggs wrote:



Tim Wescott wrote:

Steven K. Moore wrote:

In my line of work, we extract the magnitude and phase of a response
signal when the excitation signal is known. The excitation is of
the form A*sin(wt) and the response is of the form B*sin(wt+theta) +
noise. The response is sampled 16 times over a full period. Let's
denote the sampled response as R[0] through R[15]. Then the inphase
(real) and quadrature (imag) components are extracted by:

real = sum(i=0 to 15) of [R*cos(2*pi()*i/16)]
imag = sum(i=0 to 15) of [R*sin(2*pi()*i/16)]

From this the magnitude and phase of the response signal is determined.

My question is what is this technique called? I'm sure there is a
common name for it. Some of my colleagues refer to it as a DFT
(Discrete Fourier Transform). Since only a single frequency
component is being extracted, I don't feel this is proper
nomenclature. I'm looking for a more correct term to use to refer
to this single frequency extraction technique. Does anyone have a
good name for this?

Thanks,




I call it I/Q demodulation. Yes, it is a single-frequency DFT as
well, but thats a pretty fancy name for a pretty simple operation.


Nah- it's called "coherent detection" generally because there is
coherence between his sampling frequency and the signal frequency.

I've seen it called any number of things, including things not even
repeatable here. So we probably have licence to call it pretty much
anything we want. How about if I call it "Fred Bloggs" from now on, and
you call it "Tim Wescott".
Click to expand...

Is it incoherent or noncoherent detection for you?
 
Steven K. Moore wrote:

In my line of work, we extract the magnitude and phase of a response signal
when the excitation signal is known. The excitation is of the form
A*sin(wt) and the response is of the form B*sin(wt+theta) + noise. The
response is sampled 16 times over a full period. Let's denote the sampled
response as R[0] through R[15]. Then the inphase (real) and quadrature
(imag) components are extracted by:

real = sum(i=0 to 15) of [R*cos(2*pi()*i/16)]
imag = sum(i=0 to 15) of [R*sin(2*pi()*i/16)]

From this the magnitude and phase of the response signal is determined.

My question is what is this technique called? I'm sure there is a common
name for it. Some of my colleagues refer to it as a DFT (Discrete Fourier
Transform). Since only a single frequency component is being extracted, I
don't feel this is proper nomenclature. I'm looking for a more correct term
to use to refer to this single frequency extraction technique. Does anyone
have a good name for this?

Thanks,
your colleagues are correct.
Click to expand...

there are formulars that work much faster than the conventional math
used in basic DFT/IDFT (inverse....)_
FFT is commonly used.. (Fast fourier Transforms)/
if you want to see more code like this.
search google for files.
fourier.pas,FFT.pas, FFT.C, FFT.CPP etc..

you will find lots of examples.
 
Fred Bloggs wrote:

Tim Wescott wrote:

Fred Bloggs wrote:



Tim Wescott wrote:

Steven K. Moore wrote:

In my line of work, we extract the magnitude and phase of a
response signal when the excitation signal is known. The
excitation is of the form A*sin(wt) and the response is of the form
B*sin(wt+theta) + noise. The response is sampled 16 times over a
full period. Let's denote the sampled response as R[0] through
R[15]. Then the inphase (real) and quadrature (imag) components are
extracted by:

real = sum(i=0 to 15) of [R*cos(2*pi()*i/16)]
imag = sum(i=0 to 15) of [R*sin(2*pi()*i/16)]

From this the magnitude and phase of the response signal is
determined.

My question is what is this technique called? I'm sure there is a
common name for it. Some of my colleagues refer to it as a DFT
(Discrete Fourier Transform). Since only a single frequency
component is being extracted, I don't feel this is proper
nomenclature. I'm looking for a more correct term to use to refer
to this single frequency extraction technique. Does anyone have a
good name for this?

Thanks,





I call it I/Q demodulation. Yes, it is a single-frequency DFT as
well, but thats a pretty fancy name for a pretty simple operation.


Nah- it's called "coherent detection" generally because there is
coherence between his sampling frequency and the signal frequency.

I've seen it called any number of things, including things not even
repeatable here. So we probably have licence to call it pretty much
anything we want. How about if I call it "Fred Bloggs" from now on,
and you call it "Tim Wescott".


Is it incoherent or noncoherent detection for you?

After four beers I'm always incoherent.
Click to expand...


--
-------------------------------------------
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
 
On Fri, 27 May 2005 18:11:50 -0700, Tim Wescott wrote:
Fred Bloggs wrote:
Tim Wescott wrote:
Steven K. Moore wrote:

In my line of work, we extract the magnitude and phase of a response
signal when the excitation signal is known. The excitation is of the
form A*sin(wt) and the response is of the form B*sin(wt+theta) +
noise. The response is sampled 16 times over a full period. Let's
denote the sampled response as R[0] through R[15]. Then the inphase
(real) and quadrature (imag) components are extracted by:

real = sum(i=0 to 15) of [R*cos(2*pi()*i/16)]
imag = sum(i=0 to 15) of [R*sin(2*pi()*i/16)]

From this the magnitude and phase of the response signal is determined.

My question is what is this technique called? I'm sure there is a
common name for it. Some of my colleagues refer to it as a DFT
(Discrete Fourier Transform). Since only a single frequency
component is being extracted, I don't feel this is proper
nomenclature. I'm looking for a more correct term to use to refer to
this single frequency extraction technique. Does anyone have a good
name for this?

I call it I/Q demodulation. Yes, it is a single-frequency DFT as
well, but thats a pretty fancy name for a pretty simple operation.

Nah- it's called "coherent detection" generally because there is
coherence between his sampling frequency and the signal frequency.

I've seen it called any number of things, including things not even
repeatable here. So we probably have licence to call it pretty much
anything we want. How about if I call it "Fred Bloggs" from now on, and
you call it "Tim Wescott".
Click to expand...

I'd vote for "The Moore Detector". ;-)

Cheers!
Rich
 
On Sat, 28 May 2005 00:13:18 GMT, "Steve" <skmoore@indy.rr.com> wroth:

This is sampled first and numerically processed (aka DSP). I think of the
lock-in amp approach as analog I & Q multipliers and lowpass filters to
obtain real and imag components.
Click to expand...
Almost any analog technique can be implemented digitally by sampling
followed by digital processing. I still think your device could ne called a
lock-in amplifier. Maybe a digital lock-in amplifier?

Jim
 
"Jamie" <jamie_5_not_valid_after_5_Please@charter.net> wrote in message
news:LGQle.365$HN1.154@fe02.lga...
Steven K. Moore wrote:

In my line of work, we extract the magnitude and phase of a response
signal when the excitation signal is known. The excitation is of the
form A*sin(wt) and the response is of the form B*sin(wt+theta) + noise.
The response is sampled 16 times over a full period. Let's denote the
sampled response as R[0] through R[15]. Then the inphase (real) and
quadrature (imag) components are extracted by:

real = sum(i=0 to 15) of [R*cos(2*pi()*i/16)]
imag = sum(i=0 to 15) of [R*sin(2*pi()*i/16)]

From this the magnitude and phase of the response signal is determined.

My question is what is this technique called? I'm sure there is a common
name for it. Some of my colleagues refer to it as a DFT (Discrete
Fourier Transform). Since only a single frequency component is being
extracted, I don't feel this is proper nomenclature. I'm looking for a
more correct term to use to refer to this single frequency extraction
technique. Does anyone have a good name for this?

Thanks,
your colleagues are correct.
there are formulars that work much faster than the conventional math used
in basic DFT/IDFT (inverse....)_
FFT is commonly used.. (Fast fourier Transforms)/
if you want to see more code like this.
search google for files.
fourier.pas,FFT.pas, FFT.C, FFT.CPP etc..

you will find lots of examples.
Click to expand...

Thanks, but I'm quite fami,iar with FFT algorithms (My master thesis
developed a parallel processing spectrum analyzer based on Cooley-Tukey FFT
algorithm.) The need is not a full spectrum decomposition, but merely the
extraction of a single frequency. Sort of a DSP version of a lock-in
amplifier.

It doesn't seem that a definitive name has bubbled to the top. I've heard:
+ DFT evaluated at the resolution frequency
+ I/Q demodulation
+ coherent detection
+ Fred Bloggs :)
+ Tim Wescott :)
+ "The Moore Detector". ;-)

Thanks for all your input.
Steve Moore
 
James Meyer wrote...
On Sat, 28 May 2005 00:13:18 GMT, "Steve" <skmoore@indy.rr.com> wroth:

This is sampled first and numerically processed (aka DSP). I think of the
lock-in amp approach as analog I & Q multipliers and lowpass filters to
obtain real and imag components.


Almost any analog technique can be implemented digitally by sampling
followed by digital processing. I still think your device could ne called a
lock-in amplifier. Maybe a digital lock-in amplifier?
Click to expand...
If you wish, it's still a lock-in amp.


--
Thanks,
- Win
 
On Sat, 28 May 2005 18:28:51 GMT, "Steve" <skmoore@indy.rr.com> wroth:


It doesn't seem that a definitive name has bubbled to the top. I've heard:
+ DFT evaluated at the resolution frequency
+ I/Q demodulation
+ coherent detection
+ Fred Bloggs :)
+ Tim Wescott :)
+ "The Moore Detector". ;-)

Thanks for all your input.
Steve Moore
Click to expand...
If Win Hill says it's a lock-in amp, then it's a lock-in amp.

Jim
 
My most humble apologies. When I went back to collect all the answers
suggested, I failed to record the response from one of my most respected
voices in this newsgroup. Win, I beg your forgiveness.

Steve Moore

"James Meyer" <jmeyer@nowhere.net> wrote in message
news:e9th91l4jl5idrthdk3tcvc5ijrv0kmeva@4ax.com...
On Sat, 28 May 2005 18:28:51 GMT, "Steve" <skmoore@indy.rr.com> wroth:



It doesn't seem that a definitive name has bubbled to the top. I've
heard:
+ DFT evaluated at the resolution frequency
+ I/Q demodulation
+ coherent detection
+ Fred Bloggs :)
+ Tim Wescott :)
+ "The Moore Detector". ;-)

Thanks for all your input.
Steve Moore


If Win Hill says it's a lock-in amp, then it's a lock-in amp.

Jim
Click to expand...
 
On 28 May 2005 11:20:30 -0700, Winfield Hill
<hill_a@t_rowland-dotties-harvard-dot.s-edu> wrote:

James Meyer wrote...

On Sat, 28 May 2005 00:13:18 GMT, "Steve" <skmoore@indy.rr.com> wroth:

This is sampled first and numerically processed (aka DSP). I think of the
lock-in amp approach as analog I & Q multipliers and lowpass filters to
obtain real and imag components.


Almost any analog technique can be implemented digitally by sampling
followed by digital processing. I still think your device could ne called a
lock-in amplifier. Maybe a digital lock-in amplifier?

If you wish, it's still a lock-in amp.
Click to expand...

Why? Where's the amplifier?

John
 
John Larkin wrote...
Winfield Hill wrote:

If you wish, it's still a lock-in amp.

Why? Where's the amplifier?
Click to expand...
The "amplifier" part of the name is tradition, little more.
BTW, most modern lock-in amps are DSP based these days.


--
Thanks,
- Win
 
"Steven K. Moore" <smoore2@indy.rr.com> wrote in message
news:eek:RNle.37$XA6.2@tornado.ohiordc.rr.com...
In my line of work, we extract the magnitude and phase of a response
signal
when the excitation signal is known. The excitation is of the form
A*sin(wt) and the response is of the form B*sin(wt+theta) + noise. The
response is sampled 16 times over a full period. Let's denote the sampled
response as R[0] through R[15]. Then the inphase (real) and quadrature
(imag) components are extracted by:

real = sum(i=0 to 15) of [R*cos(2*pi()*i/16)]
imag = sum(i=0 to 15) of [R*sin(2*pi()*i/16)]

From this the magnitude and phase of the response signal is determined.

My question is what is this technique called? I'm sure there is a common
name for it. Some of my colleagues refer to it as a DFT (Discrete Fourier
Transform). Since only a single frequency component is being extracted, I
don't feel this is proper nomenclature. I'm looking for a more correct
term
to use to refer to this single frequency extraction technique. Does
anyone
have a good name for this?

Thanks,
--
Steve Moore
Steve.Moore@IEEE.org

This guy does only 4 samples per cycle, which results in serious calculation
Click to expand...

minimisation, and calls it Quadrature Direct Fourier Transform (QDFT).
see http://members.cox.net/berniekm/qdft.html

Gerhard van den Berg
 
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