Differential charge amplifier for marine seismic applications

A marine seismic streamer assembly forming an elongated streamer designed to be towed underwater for passive underwater sound detection of acoustic pressure variations and production of electrical signals to be transmitted through a long pair of twisted conductors to signal processing equipment on a towing vessel, comprising an elongated seismic streamer formed of plural, serially interconnected streamer sections, a plurality of the streamer sections each containing an array of marine hydrophones of the capacitive transducer type each responsive to varying acoustic pressure to produce a varying electrical charge output that is proportional to the acoustic pressures to which the hydrophones in the array are subjected, means directly connecting the long pair of twisted electrical conductors to the hydrophone array at an input end of the conductors to conduct the varying electric charge output from the hydrophone array to the signal processing equipment, and a differential charge amplifier connected to an output end of said pair of conductors at a location remote from said hydrophone array to respond to the varying electrical charge output from the hydrophone array and produce amplified output voltage signals representative of said varying electrical charge output, the differential charge amplifier comprising a pair of charge amplifier stages forming a pair of parallel signal processing channels each having an operational amplifier therein having negative and positive polarity inputs and an output and parallel combinations of resistance and capacitance connected from the outputs of each respective charge amplifier to the respective negative inputs thereof forming negative feedback circuits to keep the two inputs of each respective charge amplifier at the same potential level, the capacitance in each of said negative feedback circuits being the same value, means connecting the pair of conductors to the negative polarity inputs of the two respective charge amplifiers, and a differential amplifier having negative and positive polarity inputs and means connecting the outputs from said two charge amplifiers to said last-mentioned inputs for cancelling common mode signals appearing at the negative polarity inputs of said two charge amplifiers.

A marine hydrophone assembly for passive under-water sound detection of acoustic pressure variations and production of electrical signals to be transmitted through a pair of twisted conductors to signal processing equipment at a processing station spaced from an underwater listening station comprising a marine hydrophone of the capacitive transducer type at the underwater listening station responsive to varying acoustic pressure to produce a varying electrical charge output that is proportional to the acoustic pressures to which the hydrophone is subjected, means directly connecting the pair of twisted electrical conductors to the hydrophone at an input end of the conductors to conduct the varying electric charge output from the hydrophone to the signal processing equipment, and a differential charge amplifier connected to an output end of said pair of conductors at the processing station remote from said hydrophone to respond to the varying electrical charge output from the hydrophone and produce amplified output voltage signals representative of said varying electrical charge output, the differential charge amplifier comprising a pair of charge amplifier stages forming a pair of parallel signal processing channels each having an operational amplifier therein having negative and positive polarity inputs and an output and parallel combinations of resistance and capacitance connected from the outputs of each respective charge amplifier to the respective negative inputs thereof forming negative feedback circuits to keep the two inputs of each respective charge amplifier at the same potential level, the capacitance in each of said negative feedback circuits being the same value, means connecting the pair of conductors to the negative polarity inputs of the two respective charge amplifiers, and a differential amplifier having negative and positive polarity inputs and means connecting the outputs from said two charge amplifiers to said last-mentioned inputs for cancelling common mode signals appearing at the negative polarity inputs of said two charge amplifiers.

A marine hydrophone assembly for passive underwater sound detection of acoustic pressure variations and production of electrical signals to be transmitted through a pair of ungrounded twisted conductors to signal processing equipment at a processing station spaced from an underwater listening station comprising a marine hydrophone of the capacitive transducer type at the underwater listening station responsive to varying acoustic pressure to produce a varying electrical charge output that is proportional to the acoustic pressures to which the hydrophone is subjected, means directly connecting the pair of twisted electrical conductors to the hydrophone at an input end of the conductors to conduct the varying electric charge output from the hydrophone to the signal processing equipment, and a differential charge amplifier coupled to an output end of said pair of conductors at the processing station remote from said hydrophone to respond to the varying electrical charge output from the hydrophone and produce amplified output voltage signals representative of said varying electrical charge output, the differential charge amplifier comprising an operational amplifier having negative and positive polarity ungrounded inputs and an output, circuit means providing a negative feedback circuit comprising a parallel combination of resistance and capacitance coupling feedback voltage to the negative input of the operational amplifier to form a charge amplifier circuit having the property of operating substantially independent of shunt capacitance variations across its input, means coupling signals from said pair of conductors to the two inputs of the operational amplifier, and a branch circuit having a parallel combination of resistance and capacitance connected between said positive polarity input and electrical ground and having the same resistance and capacitance values as said negative feedback circuit, said last-mentioned branch circuit and said negative feedback circuit being connected directly to the positive and negative polarity inputs respectively of said operational amplifier for causing cancellation of common mode signals appearing at the inputs of said operational amplifier.

A seismic detection system for geophysical prospecting and the like by detection of acoustic pressure variations forming seismic signals and production of electrical signals to be transmitted through a pair of ungrounded twisted conductors to signal processing equipment at a processing station spaced from a seismic signal detection station, comprising a seismic sensor of the capacitive transducer type at the detection station responsive to varying acoustic pressure to produce a varying electrical charge output that is proportional to the acoustic pressures to which the sensor is subjected, means directly connecting the pair of twisted electrical conductors to the sensor at an input end of the conductors to conduct the varying electric charge output from the sensor to the signal processing equipment, and a differential charge amplifier coupled to an output end of said pair of conductors at the processing station remote from said sensor to respond to the varying electrical charge output from the sensor and produce amplified output voltage signals representative of said varying electrical charge output, the differential charge amplifier comprising an operational amplifier having negative and positive polarity ungrounded inputs and an output, circuit means providing a negative feedback circuit comprising a parallel combination of resistance and capacitance coupling feedback voltage to the negative input of the operational amplifier to form a charge amplifier circuit having the property of operating substantially independent of shunt capacitance variations across its input, means coupling signals from said pair of conductors to the two inputs of the operational amplifier, and a branch circuit having a parallel combination of resistance and capacitance connected between said positive polarity input and electrical ground and having the same resistance and capacitance values as said negative feedback circuit, said lastmentioned branch circuit and said negative feedback circuit being connected directly to the positive and negative polarity inputs respectively of said operational amplifier for causing cancellation of common mode signals appearing at the inputs of said operational amplifier.

A seismic detection system for geophysical prospecting by sound detection of acoustic pressure variations forming seismic signals and production of electrical signals to be transmitted through a pair of twisted conductors to signal processing equipment at a processing station spaced from a seismic signal detection station comprising a seismic sensor of the capacitive transducer type at the detection station responsive to varying acoustic pressure to produce a varying electrical charge output that is proportional to the acoustic pressures to which the sensor is subjected, means directly connecting the pair of twisted electrical conductors to the sensor at an input end of the conductors to conduct the varying electric charge output from the sensor to the signal processing equipment, and a differential charge amplifier connected to an output end of said pair of conductors at the processing station remote from said sensor to respond to the varying electrical charge output from the sensor and produce amplified output voltage signals representative of said varying electrical charge output, the differential charge amplifier comprising a pair of charge amplifier stages forming a pair of parallel signal processing channels each having an operational amplifier therein having negative and positive polarity inputs and an output and parallel combinations of resistance and capacitance connected from the outputs of each respective charge amplifier to the respective negative inputs thereof forming negative feedback circuits to keep the two inputs of each respective charge amplifier at the same potential level, the capacitance in each of said negative feedback circuits being the same value, means connecting the pair of conductors to the negative polarity inputs of the two respective charge amplifiers, and a differential amplifier having negative and positive polarity inputs and means connecting the outputs from said two charge amplifiers to said last-mentioned inputs for cancelling common mode signals appearing at the negative polarity inputs of said two charge amplifiers.