The WCS4000 is an integrated photo sensor that provides a wide range of optical sensitivity. The photo diode converts light signal to electrical signal. A trans-impedance amplifier will gain the signal and convert it to a voltage output. The trans-impedance gain is auto adjustable to meet the required device sensitivity 3uW to 65uW. The low pass filter (LPF) and high pass filter(HPF) filter out low and high frequency noise and provide the auto-gain adjustment over required sensitivity. Conditioning circuit is added to generate a 128 KHz digital output signal with constant duty cycle. The output buffer will provide a maximum output current drive of 2mA.