Automatic gain control apparatus which adjusts bias and gain to maximize signal to noise ratio

Claim 1

An apparatus for automatically controlling gain, comprising: receiving means for receiving optical signals, and for generating electrical signals corresponding to the received optical signals using an adjustable multiplication factor which depends on an applied bias signal; variable gain control means for amplifying the electrical signals from the receiving means by an adjustable gain; difference determining means for determining a difference between an electrical signal from the gain control means and a reference signal; and producing means, responsive to a determined signal indicative of said difference from the difference determining means, for controlling a gain of said variable gain control means and for producing the bias signal such that: (1) when a value of the determined signal is less than or equal to a first predetermined value, the multiplication factor is set to a first constant value, and said gain of the variable gain control means is controlled corresponding to a level of said received optical signals, (2) when a value of the determined signal is greater than or equal to a second predetermined value greater than said first predetermined value, the multiplication factor is set to a second constant value less than said first constant value and said gain of the variable gain control means is controlled corresponding to the level of said received optical signals, and (3) when a value of said determined signal is between said first and second predetermined values, said bias signal is controlled corresponding to said difference, and said gain is controlled corresponding to the level of said received optical signals.

Claim 2

An apparatus for automatically controlling gain, comprising: receiving means for receiving optical signals, and for generating electrical signals corresponding to the received optical signals using an adjustable multiplication factor which depends on an applied bias signal; variable gain control means for amplifying the electrical signals from the receiving means by an adjustable gain; difference determining means for determining a difference between an electrical signal from the gain control means and a reference signal; and producing means, responsive to a determined signal indicative of said difference from the difference determining means, for controlling a gain of said variable gain control means and for producing the bias signal such that: (1) when a value of the determined signal is less than or equal to a first predetermined value, the multiplication factor is set to a first constant value, and said gain of the variable gain control means is controlled corresponding to a level of said received optical signals, (2) when a value of the determined signal is greater than or equal to a second predetermined value greater than said first predetermined value, the multiplication factor is set to a second constant value less than said first constant value and said gain of the variable gain control means is controlled corresponding to the level of said received optical signals, and (3) when a value of said determined signal is between said first and second predetermined values, said bias signal is controlled corresponding to said difference, and said gain is controlled corresponding to the level of said received optical signals.

Claim 9

An apparatus for automatically controlling gain, comprising: receiving means for receiving optical signals, and for generating electrical signals corresponding to the received optical signals using an adjustable multiplication factor which depends on an applied bias signal; variable gain control means for amplifying the electrical signals from the receiving means by an adjustable gain; difference determining means for determining a difference between an electrical signal from the gain control means and a reference signal, and for controlling a gain of the variable gain control means corresponding to the difference; producing means, responsive to a determined signal indicative of said difference from the difference determining means, for producing the bias signal to set the multiplication factor to a first value when a value of the determined signal is less than or equal to a first predetermined value, and to set the multiplication factor to a second value, which is greater than the first value, when a value of the determined signal greater than or equal to a second predetermined value; memory means for storing predetermined data corresponding to various ambient temperatures; detecting means for detecting an ambient temperature and applying the ambient temperature to the memory means to read out data corresponding thereto; and generating means responsive to data for generating signals corresponding to the first and second predetermined values.

Claim 10

An apparatus for automatically controlling gain, comprising: receiving means for receiving optical signals, and for generating electrical signals corresponding to the received optical signals using an adjustable multiplication factor which depends on an applied bias signal; variable gain control means for amplifying the electrical signals from the receiving means by an adjustable gain; difference determining means for determining a difference between an electrical signal from the gain control means and a reference signal, and for controlling a gain of the variable gain control means corresponding to the difference; producing means, responsive to a determined signal indicative of said difference from the difference determining means, for producing the bias signal to set the multiplication factor to a first value when a value of the determined signal is less than or equal to a first predetermined value, and to set the multiplication factor to a second value, which is greater than the first value, when a value of the determined signal greater than or equal to a second predetermined value; memory means for storing predetermined data corresponding to various ambient temperatures; detecting means for detecting an ambient temperature and applying the ambient temperature to the memory means to read out data corresponding thereto; and generating means responsive to data for generating signals corresponding to the first and second predetermined values.