Hydrophone Preamplifier and Calibration Circuit.
DEPARTMENT OF THE NAVY WASHINGTON DC
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The present invention comprises a hydrophone preamplifier for coupling to a remote load and DC voltage supply through a single 2-wire cable. The preamp comprises a hybrid amplifier having a high-impedance input stage comprising a reverse-biased junction FET and an amplifier transistor output stage, the output voltage being fed to a current driver stage which is in series with the remote DC supply voltage and low-valued load resistor. The preamp completely controls the cable current, both supply and signal, by use of a constant-current diode which is inserted in the DC voltage supply line between its connection to the current-driver and the amplifier. A diode zener diode in parallel with a capacitor is placed across the amplifier from its dc supply voltage side to its ground side to compensate for differences in the constant-current supply from the constant-current diode and the varying current demanded by the amplifier. To couple in an AC calibration signal which is superimposed on a DC level, an optoisolator is connected to the preamplifier input so that its output signal is in series with the hydrophone signal although only one signal is used at a time. In an array of hydrophones and preamps, the optoisolators are connected in series so that only a single calibration source is required and each preamp receives the same calibration signal. Author
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