| 摘要 |
A pulse oximeter or plethysmographic device utilizes light varying in intensity at a predetermined carrier frequency. A passive resonant circuit having a resonant frequency substantially equal to the carrier frequency is connected between the photodetector and the first amplifier. The resonant circuit serves to suppress spurious DC and low frequency components such as those due to ambient light and ambient light flicker and also to suppress high frequency interference. Because ambient light signals are suppressed, there is no need for dark current correction or restoration. Suppression of ambient light and other interference upstream of the front end amplifier avoids saturation of the amplifier and permits use of a front end amplifier having high gain. |
