Patent ID: 7994460

Claim:
A method for controlling the position of a beam of light, comprising: directing a beam of amplitude modulated (AM) light onto a position sensitive detector (PSD), wherein said AM light is modulated at a modulation frequency, wherein said PSD will produce a first current (I 1 ) and a second current (I 2 ), wherein said I 1 and said I 2 vary ratiometrically depending on where said beam is located on said PSD; converting said I 1 to a first voltage (V 1 ) and converting said I 2 to a second voltage (V 2 ); subtracting said V 2 from said V 1 to produce a difference signal; digitally normalizing said difference signal to produce a normalized signal; controlling, using said normalized signal, said position of said beam of light on said PSD; adding said V 1 to said V 2 to produce a sum signal; filtering said difference signal with a first bandpass filter to produce a filtered difference signal; filtering said sum signal with a second bandpass filter to produce a filtered sum signal; amplifying said filtered difference signal with a first variable gain amplifier system to produce a first amplified difference signal; amplifying said filtered sum signal with a second variable gain amplifier system to produce a first amplified sum signal; detecting said first amplified sum signal with an automatic gain control (AGC) detector to produce a detected sum signal; inputting said detected sum signal to an automatic gain control controller to produce a received signal strength indicator (RSSI); and feeding said RSSI back to said first variable gain amplifier system to produce an amplified difference output signal that is modulated at said modulation frequency.