Hi Chuck

This isn't quite noise though. Noise is generally random and can't be
distinguished from the signal. There's really nothing you can do to remove
noise. What you have is interference at a known frequency that is well
outside the frequency range of the signal you are interested in. So it
should be possible to use a low pass filter to remove the switching
artifacts.  What is the cut-off frequency of your filter?

What's the DC offset to the signal input of the LT1043? This will be
modulated by the clock and require a large amount of filtering to remove.

Matt

On Tue, May 18, 2010 at 3:11 PM, Chuck / Judy Burch wrote:

>
> Thanks Matt, Karl and Chris for your responses.
>
> I am currently using a modified version of the PSD described on page 4 of
> Linear Tech's Application Note #3.  I use an amplitude stabilized Wien
> bridge oscillator (5000 Hz) for excitation.  The reference signal goes to an
> LF1011 comparator that drives an LT1034.  The amplified signal goes to the -
> input of  an LT1007;  the LT1043 switches the + input between ground and the
> signal so that the LT1007 acts as a synchronous detector.  (This circuit is
> also described in US patent #3940693.)  This is followed by a 2 pole LPF.
>
> This arrangement works fine.  The LPF eliminates the excitation artifacts.
>  But the switching pulses still come through.
>
> Shielding does not help the pulse problem, so I conclude that what I'm
> seeing on the downstream part of my boards is magnetic or EM propagated
> pickup.  Steel enclosures and/or ferrite beads might help, but I haven't
> tried either.
>
> On the argument that eliminating a noise source is better than trying to
> filter or shield it, I wondered if other PSD designs might be intrinsically
> quieter.
>
> I will try slowing the rise-time of the clock signal going to the LT1043
> and I have a Maxim DG419 switch on order to try as well.
>
> I'll report in the event I have any success.
>
>
> Chuck
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>
> Public Seismic Network Mailing List (PSN-L)
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>
Hi Chuck

This isn't quite noise though. Noise is gen=
erally random and can't be distinguished from the signal. There's r=
eally nothing you can do to remove noise. What you have is interference at =
a known frequency that is well outside the frequency range of the signal yo=
u are interested in. So it should be possible to use a low pass filter to r=
emove the switching artifacts. =A0What is the cut-off frequency of your fil=
ter?

What's the DC offset to the signal input of the LT1=
043? This will be modulated by the clock and require a large amount of filt=
ering to remove.

Matt


On Tue, May 18, 2010 at 3:11 PM, Chuck / Judy Burch <<=
a href=3D"mailto:cjburch@...........">cjburch@...........> wr=
ote:



Thanks Matt, Karl and Chris for your responses.



I am currently using a modified version of the PSD described on page 4 of L=
inear Tech's Application Note #3. =A0I use an amplitude stabilized Wien=
 bridge oscillator (5000 Hz) for excitation. =A0The reference signal goes t=
o an LF1011 comparator that drives an LT1034. =A0The amplified signal goes =
to the - input of =A0an LT1007; =A0the LT1043 switches the + input between =
ground and the signal so that the LT1007 acts as a synchronous detector. =
=A0(This circuit is also described in US patent #3940693.) =A0This is follo=
wed by a 2 pole LPF.




This arrangement works fine. =A0The LPF eliminates the excitation artifacts=
.. =A0But the switching pulses still come through.



Shielding does not help the pulse problem, so I conclude that what I'm =
seeing on the downstream part of my boards is magnetic or EM propagated pic=
kup. =A0Steel enclosures and/or ferrite beads might help, but I haven't=
 tried either.




On the argument that eliminating a noise source is better than trying to fi=
lter or shield it, I wondered if other PSD designs might be intrinsically q=
uieter.



I will try slowing the rise-time of the clock signal going to the LT1043 an=
d I have a Maxim DG419 switch on order to try as well.



I'll report in the event I have any success.





Chuck

__________________________________________________________



Public Seismic Network Mailing List (PSN-L)



To leave this list email PSN-L-REQUEST@.............. with the body of the messa=
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See h=
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