US 4,214,215 AGranted

Low noise-high gain JFET amplifier for a piezoelectric transducer

AssigneeContact Communication Corporation

InventorsArthur J. Mellen, Adolf Reitlinger

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Abstract

A low-noise junction field effect depletion mode transistor amplifier and a signal retrieval network therefor is described. The junction (JFET) is used to amplify the signal from a piezoelectric transducer which forms the sensing element of a bone conduction microphone. A conventional transistor or Darlington pair is provided with a base electrode coupled to the source electrode of the JFET and a collector electrode coupled to the JFET drain electrode. The emitter circuit of the transistor includes a first voltage divider for feeding back a portion of the emitter signal to the base circuit of the transistor and another portion to the gate circuit of the JFET through the piezoelectric transducer. A second voltage divider is provided in the feedback path from the first divider to the transistor base to apply a portion of the base feedback signal to the JFET gate through the gate input resistor. By suitably selecting a high enough bias voltage for the JFET and by provision of the output transistor and associated feedback, the amplified output signal can be taken from either of the D.C. bias supply lines, namely, the positive line from the drain electrode of the JFET or the negative supply line at the bottom of the first voltage divider. Further solid state circuit means are provided for retrieving the amplified output signal from either of said supply lines with maximum gain and signal output.

Claims6

Dependent claims

A two wire sensing transducer and amplifier combination, comprising

a piezoelectric transducer having first and second electrical leads,
a junction field effect transistor (JFET) having drain, source, and gate electrodes,
a first transistor having collector, emitter, and base electrodes,
means for connecting one lead of the transducer to the gate electrode of said JFET,
means for connecting said source and base electrodes together,
first and second terminals connected, respectively, to said drain and collector electrodes and to the second lead of the transducer,
a first voltage divider connected between said emitter electrode and said second terminal,
a second voltage divider connected between said connected source and base electrodes and said first voltage divider, thereby to provide a first bootstrapping feedback connection to the base of the transistor means,
a resistor means connected between said gate electrode and said second voltage divider, thereby to provide a second bootstrapping feedback connection to the gate of the JFET,
first and second supply lines for providing connection to a D.C. voltage source,
means for coupling said first and second terminals to said first and second supply lines, respectively, and
output circuit means connected between said supply lines and separate from said transistor means and from said first and second terminals for coupling from said supply lines an output signal produced by said combination of transducer and amplifier.

9 more elements

Dependencies are inferred from the claim text.