A method and system for optical measuring one or more vital signs of a human is described. The method includes generating an optical Pulse Width Modulated (PWM) signal modulated in accordance with a predetermined Pulse Width Modulation scheme. The PWM scheme includes one or more Pulse Width Modulations having different modulation frequencies. The method also includes applying the PWM optical signal to a measurement location in a blood perfused body tissue of the human and receiving light originated back from the measurement location. A photo current signal of a time response of the blood perfused body tissue to the PWM optical signal is indicative of the vital signs. The method includes generating a voltage signal from the photo current signal and processing the voltage signal for determining the vital signs.