Technical Supplement
S-12
Filters then remove noise and smooth the signals before sending them
to the amplifiers.
• Signal gain —The separated LED signals are amplified so that their
current levels are within the A/D converter's acceptable range. The
signals are filtered to improve the signal-to-noise ratio, and clamped to
a reference voltage.
• AC ranging —DC offset is eliminated from each LED signal. An
analog switch sets the mean signal value to the mean of the A/D
converter range, and the AC modulation is superimposed on that DC
level. Then, each AC signal is amplified and filtered to eliminate
residual effects of the PWM modulations. Finally, these two signals are
input to the CPU A/D converter.
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