Class-d BICMOS hearing aid output amplifier

An integrated circuit hearing aid amplifier comprising:

• a front end circuit including
• an oscillator,
• an integrator built with bipolar transistors coupled to an output of said oscillator and having a microphone input,
• a comparator built with bipolar transistors and having a differential input with first and second input terminals, said first input terminal being coupled to an output of said integrator,
• a voltage reference generator built with bipolar transistors and having an output coupled to said second input terminal of said comparator, wherein said voltage reference generator includes components matching components of said integrator such that a voltage output of said voltage reference generator will vary with temperature in the same manner as said integrator output;
• an MOS output driver coupled to an output of said front end circuit;
• a battery input coupled to said MOS output driver;
• and
• a voltage regulator having an input coupled to said battery input and an output coupled to said front end circuit to provide a front end voltage supply isolated from said battery input.

A hearing aid amplifier comprising:

• an oscillator,
• an integrator coupled to an output of said oscillator and having a microphone input,
• a comparator having a differential input with first and second input terminals, said first input terminal being coupled to an output of said integrator,
• a voltage reference generator having an output coupled to said second input terminal of said comparator, wherein said voltage reference generator includes components matching components of said integrator such that a voltage output of said voltage reference generator will vary with temperature in the same manner as said integrator output;
• and
• an output driver coupled to an output of said comparator.

A hearing aid amplifier comprising:

• an oscillator,
• an integrator coupled to an output of said oscillator and having a microphone input,
• a comparator having a differential input with first and second input terminals, said first input terminal being coupled to an output of said integrator,
• a voltage reference generator having an output coupled to said second input terminal of said comparator, wherein said voltage reference generator includes components matching components of said integrator such that a voltage output of said voltage reference generator will vary with temperature in the same manner as said integrator output;
• and
• an output driver coupled to an output of said comparator;
• wherein said output driver is constructed with MOS transistors and said oscillator, integrator, comparator and voltage reference generator are constructed with bipolar transistors, and further comprising a level converter coupled between said comparator and said output driver for converting bipolar levels to MOS levels.

A hearing aid amplifier comprising:

• an oscillator;
• a microphone input;
• an integrator coupled to an output of said oscillator, said microphone input being coupled to said integrator;
• a comparator having a differential input with first and second input terminals, a plurality of cascaded differential bipolar transistor pairs coupled to said input terminals, each transistor pair being coupled between a current source and load resistors, said load resistors being coupled to a voltage supply, said first input terminal being coupled to an output of said integrator;
• a voltage reference generator having an output coupled to said second input terminal of said comparator;
• an MOS output driver coupled to an output of said comparator;
• a battery input coupled to said MOS output driver;
• and
• a voltage regulator having an input coupled to said battery input and an output coupled to said voltage supply for said oscillator, integrator and comparator to provide a voltage supply isolated from said battery input.

A hearing aid amplifier comprising:

• an oscillator;
• a microphone input;
• an integrator coupled to an output of said oscillator, said microphone input being coupled to said integrator, said integrator including a differential bipolar transistor pair coupled to said oscillator output and a current source, a first resistor coupled between said transistor pair and said integrator output, a second resistor coupled between said integrator output and said microphone input, and a first capacitor coupled between said integrator output and a front end voltage supply;
• a comparator having a differential input with first and second input terminals, said first input terminal being coupled to an output of said integrator;
• a voltage reference generator having an output coupled to said second input terminal of said comparator, said voltage reference generator including components matching components of said integrator such that a voltage output of said voltage reference generator will vary with temperature in the same manner as said integrator output, said voltage reference generator including a bipolar transistor coupled to a current source, a third resistor coupled to said bipolar transistor, a fourth resistor coupled between said third resistor and said voltage reference generator output and a second capacitor coupled between said voltage reference generator output and said front end voltage supply;
• an MOS output driver coupled to an output of said comparator;
• a battery input coupled to said MOS output driver;
• and
• a voltage regulator having an input coupled to said battery input and said front end voltage supply as an output coupled to said oscillator, integrator and comparator to provide a voltage supply isolated from said battery input.

A BICMOS integrated circuit hearing aid amplifier comprising:

• a front end circuit built with bipolar transistors including an oscillator and having a microphone input;
• an MOS output driver coupled to an output of said front end circuit;
• a battery input coupled to said MOS output driver;
• a voltage regulator having an input coupled to said battery input and an output coupled to said front end circuit to provide a front end voltage supply isolated from said battery input;
• and
• level converter means, coupled between said front end circuit and said MOS output driver, for converting bipolar levels to MOS levels.