Gain compression amplfier providing a linear compression function

A compression amplifier having a wide dynamic range and configured to provide selective gain compression, comprising:

• an amplifier having an input and an output;
• a gain control circuit having an input coupled to said amplifier output and an output, said gain control circuit being responsive to an output signal on said amplifier output and to a predetermined threshold signal for generating an output gain control current;
• and
• a current controlled gain controller having a first input connected to said amplifier output, a second input connected to said gain control circuit output, and an output connected to said amplifier input, said gain controller being responsive to said gain control current such that when said gain control current changes said gain controller adjusts the gain of said amplifier;
• wherein said gain control current is defined by:
• ##EQU15## and wherein said gain control circuit includes:
• a rectifier circuit portion having an input coupled to said output of said amplifier and an output, said output of said rectifier circuit portion providing a rectified DC signal;
• a signal comparing circuit portion receiving said rectified DC signal and said predetermined threshold signal for generating an output signal that is a difference between said rectified DC signal and said predetermined threshold signal;
• a summing circuit portion having a first input coupled to said output of said signal comparing circuit portion and a second input coupled to a sub-threshold amplifier, said summing circuit portion generating an output signal that is a sum of the signals on said first and second inputs;
• and
• a current generating circuit portion having an input coupled to said output of said summing circuit and an output coupled to said gain controller, said current generating circuit portion generating said gain control current which is proportional to said rectified DC signal and said predetermined threshold signal.

A hearing aid comprising:

• a preamplifier network having an input connected to a sound detector and an output, wherein said preamplifier network includes a compression amplifier having an amplifier with an input leg and an output leg corresponding to said output of said preamplifier network, a gain controller coupled between said input and output legs of said amplifier, said gain controller being responsive to a gain control signal to permit continuous gain adjustment of said amplifier, and a gain control circuit having an input coupled to said amplifier output and output coupled to said gain controller, said gain control circuit for comparing an output voltage on said amplifier output with a predetermined threshold signal and for generating said gain control signal on said gain control circuit output so as to provide continuous gain adjustment of said amplifier at least when said amplifier output signal is greater than said predetermined threshold signal;
• and
• an output drive network having an input connected to said output of said preamplifier network and an output connected to a sound transducer, said output drive network including an amplifier having a fixed gain, wherein said preamplifier network gain control circuit includes:
• a rectifier circuit portion having an input coupled to said output of said amplifier and an output, said output of said rectifier circuit portion providing a rectified voltage;
• a voltage comparing circuit portion receiving said rectified voltage and said predetermined threshold voltage and generating an output signal that is a difference between said rectified voltage and said predetermined threshold voltage;
• a summing circuit portion having a first input coupled to said output of said voltage comparing circuit portion and a second input coupled to a sub-threshold amplifier, said summing circuit portion generating an output signal that is a sum of the signals on said first and second inputs;
• and
• a current generating circuit portion having an input coupled to said output of said summing circuit and an output coupled to said gain controller, said current generating circuit generating a gain control current that is proportional to said rectified voltage and said predetermined threshold voltage.

A hearing aid comprising:

• a preamplifier network having an input connected to a sound detector and an output;
• and
• an output drive network having an input connected to said output of said preamplifier network and an output connected to a sound transducer, said output drive network including a compression amplifier having an amplifier with an input leg and an output leg corresponding to said output drive network output, a gain controller coupled between said input and output legs of said output drive network amplifier, said gain controller being responsive to a gain control signal for providing continuous gain adjustment of said output drive network amplifier, and a gain control circuit having an input coupled to said output drive amplifier output and output coupled to said gain controlling device, said gain control circuit for comparing an output voltage on said output drive network amplifier output with a predetermined threshold signal and for generating said gain control signal on said gain control circuit output so as to provide continuous gain adjustment of said output network amplifier at least when said output drive network amplifier output signal is greater than said predetermined threshold signal, wherein said output drive network gain control circuit includes:
• a rectifier circuit portion having an input coupled to said output of said output drive network amplifier and an output, said output of said rectifier circuit portion providing a rectified voltage;
• a voltage comparing circuit portion receiving said rectified voltage and said predetermined threshold voltage and generating an output signal that is a difference between said rectified voltage and said predetermined threshold voltage;
• a summing circuit portion having a first input coupled to said output of said voltage comparing circuit portion and a second input coupled to a sub-threshold amplifier, said summing circuit portion generating an output signal that is a sum of the signals on said first and second inputs;
• and
• a current generating circuit portion having an input coupled to said output of said summing circuit and an output coupled to said gain controller, said current generating circuit generating a gain control current that is proportional to said rectified voltage and said predetermined threshold voltage.