Impedance circuit for a miniature hearing aid

An amplifier buffer circuit for transforming a signal generated by a first transmission medium with a high impedance so that a second transmission medium can further manipulate the signal in a miniature hearing aid comprising:

• means for receiving the signal generated by the first transmission medium;
• a depletion mode transistor having a buried channel which prevents trapping from occurring on the surface of the depletion mode transistor and which reduces noise in the operation of the depletion mode transistor device, the depletion mode transistor being coupled to the receiving means, the depletion mode transistor reducing the impedance between the first transmission medium and the second transmission medium;
• means coupled to the depletion mode transistor for conveying the signal to the second transmission medium;
• and,
• D.C. biasing means coupled to the depletion mode transistor for imposing a D.C. on the depletion mode transistor while maintaining the high impedance of the depletion mode transistor at the receiving means, the biasing means comprising two biasing elements including at least one transistor.

A circuit for reducing the impedance between a first A.C. transmission medium and a second transmission medium comprising:

• a first transistor having a gate, a source, a drain, and a backside terminal;
• a second transistor having a gate, a source, a drain, and a backside terminal;
• a third transistor having a buried channel, and having a gate, a source, a drain, and a backside terminal;
• a first coupling means for coupling the backside terminals of the first and second transistors to the source terminal of the third transistor, wherein the first coupling means includes an output for coupling to the second transmission medium;
• and,
• a second coupling means for coupling the gate terminal of the first transistor and the source terminal of the second transistor to the gate terminal of the third transistor, wherein the second coupling means includes an input for coupling to the first transmission medium.