Decision directed gain control

Claim 1

In a receiver having decoding means for decoding a baseband multilevel signal into a digital data signal, said decoding means comprising quantizing means for quantizing said multilevel signal into discrete amplitude ranges and producing in response to each discrete amplitude range a unique combination of bits including a plurality of data bits in descending order of significance to form said data signal and a less significant soft bit, an arrangement for automatically controlling the amplitude of said multilevel signal comprising: an EXCLUSIVE-OR gate connected to said quantizing means and having a first output for producing a modulo-two sum of said soft bit and said most significant bit and a second output for producing the complement of said sum; an integrating differential amplifier having an output, an inverting input connected to said first EXCLUSIVE-OR gate output and a non-inverting input connected to said second EXCLUSVIE-OR gate output; resistance means connected in series in the path of said multilevel signal; and a transistor having its gate electrode connected to the output of said differential amplifier and its source-drain path connected from a point on said multilevel signal path between said resistance means and said quantizing means to ground.