S
Steve Sands
- Jan 1, 1970
- 0
A question for the experts here.
I understand the theory of a tuned amplifier or synchronous detector
but I have difficulty understanding the benefits. The concept, as I
understand it, is that by using a synchronous reference signal that is
in phase with a chopper or modulator that modulates a signal of
interest to gate a multiplier at some point in the gain stage, you can
realize significant improvements in signal to noise ratio.
Case in point.
In the coating industry we work with lock in amplifiers to recover
small incident reflectivity signals inside a vacuum chamber where
there are several spurious artifacts both DC and AC, that reside in
the same wavelengths as the incident or targeted reflection signals
do. The source illumination is modulated via a chopper wheel and a
reference signal is locally generated at the chopper to provide a
synchronous signal to recover the incident or reflectance signal at a
multiplier or gated amplifier.
The question is what difference does it make to only look at the
signal during the period which it is present (light enabled) versus
when it isn't (dark)?
All of the unwanted spurious reflections and artifacts are present
during this synchronous "light on period" as the "dark period"
therefore what is the advantage?
I should point out that chopping also permits blocking of DC artifacts
from heaters and other sources by using Capacitively-coupled gain
stages.
I know there is a Google optics NG but they are 99% optics 1%
equipment.
I understand the theory of a tuned amplifier or synchronous detector
but I have difficulty understanding the benefits. The concept, as I
understand it, is that by using a synchronous reference signal that is
in phase with a chopper or modulator that modulates a signal of
interest to gate a multiplier at some point in the gain stage, you can
realize significant improvements in signal to noise ratio.
Case in point.
In the coating industry we work with lock in amplifiers to recover
small incident reflectivity signals inside a vacuum chamber where
there are several spurious artifacts both DC and AC, that reside in
the same wavelengths as the incident or targeted reflection signals
do. The source illumination is modulated via a chopper wheel and a
reference signal is locally generated at the chopper to provide a
synchronous signal to recover the incident or reflectance signal at a
multiplier or gated amplifier.
The question is what difference does it make to only look at the
signal during the period which it is present (light enabled) versus
when it isn't (dark)?
All of the unwanted spurious reflections and artifacts are present
during this synchronous "light on period" as the "dark period"
therefore what is the advantage?
I should point out that chopping also permits blocking of DC artifacts
from heaters and other sources by using Capacitively-coupled gain
stages.
I know there is a Google optics NG but they are 99% optics 1%
equipment.