Patent ID: 7276684

Claim:
A non-preflash pulsed light emission and photodetector system, comprising: a photocell circuit comprising at least one photodiode and at least one transistor configured to provide an output signal, the photodiode being connected to the transistor at least one current source circuit configured to provide a holding current to the transistor, and at least one light-emitting diode (“LED”) configured to provide light to the photodiode and to be driven according to the output signal provided by the transistor; wherein the current source circuit is configured to be switched off when the photodiode is stimulated by light emitted by the LED, the photodiode being configured to generate a photocurrent when light emitted by the LED is incident thereon, the transistor being configured to amplify the photocurrent to provide an amplified photostimulus current as the output signal therefrom, the current source circuit being configured to be switched on when the LED is not emitting light and the photodiode is not being stimulated thereby to provide a holding current to the transistor to maintain a substantially constant DC operating point voltage in the transistor when no amplified photostimulus current is being generated by the transistor in response to the photodiode not generating the photocurrent.