Biomedical Engineering Reference
In-Depth Information
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FIGURE 17.11
Typical time domain noises recorded by oscilloscope under the following conditions: (a) open-input front-end circuit
(no bR photoreceptor is attached), (b) bR photoreceptor in the dark, and (c) bR photoreceptor under constant illu-
mination of a laser beam with a wavelength of 568 nm and illumination power of 0.75 mW.
To measure the SNR, the input light to the bR photoreceptor is modulated, which allows
the bR photoreceptor to respond to light intensity changes. A laser beam, with a wave-
length of 568 nm, is used as the light source and is modulated at a frequency of 10 Hz by
means of an optical chopper that is placed in the beam path. An oscilloscope is used to
record the time-domain signal. The data acquisition rate is 400 Hz, since the integration
time of the switched integrator is set to be 20 ms (i.e., 50 Hz), thus preventing the aliasing
