Low noise electronic circuit, transducer using the same, and method

• US 3,967,064 A
• Filed: 04/28/1975
• Issued: 06/29/1976
• Est. Priority Date: 11/16/1972
• Status: Expired due to Term

• Current Assignee: New SD, Inc.
• Original Assignee: Systron Donner Corporation
• Inventors: Sigworth, Frederick J.
• Primary Examiner(s): Olms, Douglas W.
• Application Number:
  US05/572,267
• Time in Patent Office: 428 Days
• Field of Search: 179/1 P, 328/1, 307/308, 331/65, 340/186, 340/262
• US Class Current: 381/94.9
• CPC Class Codes: G01D 5/2216 by a movable ferromagnetic element, e.g. a core

Abstract

An electronic circuit and method used in conjunction with transducers for eliminating noise signals which includes an AC source of excitation for first and second transducer coils, called pickoff coils located in first and second signal channels. Output from the pickoffs is supplied to detectors disposed in each of the signal channels. The detected pickoff output signals are filtered and connected to a summing circuit wherein the internally generated noise from the AC source appearing as common mode signals in both signal channels is cancelled and differential mode signals produced in said channels are added to produce an output.

Claims

1. In a transducer, means forming first and second signal channels each having an input and an output, common source means for supplying an oscillatory signal to the input of each of said signal channels, each of said signal channels including pickoff means, means connecting said pickoff means to said source means, a tuned circuit including said pickoff means for increasing excitation of said pickoff means provided by said oscillatory signal, siad increased excitation being limited only by the power dissipation characteristics of said pickoff means, detector means connected to the output of each of said signal channels, and means for summing the outputs of the channels, including a preamplifier for receiving the outputs from the signal channels and producing an output, and a differential amplifier connected to receive the output of said preamplifier and producing an output, said preamplifier and said differential amplifier each having respective input noise characteristics, said preamplifier input noise characteristic being less than said differential amplifier input noise characteristic, whereby said preamplifier operates to provide a predominant noise component at the output thereof, which when combined with the differential amplifier input noise characteristic provides a high signal to noise ratio at the output of said differential amplifier, said means forming first and second signal channels being free of active devices having three or more electrodes to thereby minimize internally generated asynchronous noise in the channels.

2. A transducer as in claim 1 together with filter means in each channel connected to the detector.

3. A transducer as in claim 1 wherein said preamplifier consists of two low-noise transistors of the type having a base, an emitter, and a collector connection, a connection from each of said signal channel outputs to a separate one of the base connections, said preamplifier output appearing between said collectors, a connection from each of said collectors to said differential amplifier input, and a common emitter connection between said low-noise transistors, whereby differential mode signals received from said channels are amplified prior to connection to said differential amplifier and common mode signals received from said channels are summed at said common emitter connection.

4. In a low noise electronic circuit for use with transducers of the type having first and second signal channels, an AC source for exciting said first and second signal channels, first and second pickoffs located in said first and second signal channels respectively connected to said Ac source and producing first and second signals, and a movable element disposed between said first and second pickoffs, a tuned circuit in each of said first and second signal channels including said first and second pickoffs for increasing said AC source excitation in said pickoffs limited only by the power dissipation characteristics of said pickoffs, means for detecting said first and second signals producing DC signals of opposite polarity, said detecting means minimizing injection of asynchronous noise into said channels, means for summing said DC signals whereby common mode signals are cancelled and differential mode output signals are added, and amplifying means for receiving said added differential mode signals and for shaping signal response characteristics.

5. In a low noise electronic circuit for use with transducers of the type having first and second signal channels, an AC source for exciting first and second pickoffs located in each of said first and second signal channels and producing first and second signals therein, and a movable element disposed between said pickoffs, means for amplifying said AC source excitation in said pickoffs limited only by the power dissipation characteristics of said pickoffs, means for detecting said signals in each of said first and second channels producing DC signals of like polarity said detecting means minimizing injection of asynchronous noise into said channels, means for summing and amplifying the common mode output and the differential mode output from said signal channels, a differential amplifier sensitive to said amplified differential mode output for providing system output, a feedback path, an amplifier disposed in said feedback path sensitive to said amplified common mode output, and output from said amplifier in said feedback path providing negative feedback to said AC source, said feedback operating to further reduce residual output noise by reducing common mode level variations in said channels.

6. A low noise electronic circuit for use with transducers as in claim 5 wherein said means for summing and amplifying the common mode output and the differential mode output from said signal channels comprises a low noise transistor pair of the type having base, emitter, and collector connections disposed to each receive the output from one of said signal channels at their base connections, whereby an amplified differential output is provided between one pair of output points for the pair and a summed and amplified common mode output is provided at another common pair of output points.

7. The method of providing a low noise electronics circuit for use with transistors, comprising the steps of generating an AC excitation signal, exciting a pickoff in each of said two separate signal channels by directly connecting the pickoffs to the AC signal, tuning each of said pickoffs to increase said AC excitation signal limited only by the power dissipation capability of said pickoffs, moving a conductive element between said pickoffs to produce an output signal in each of said signal channels, detecting said output signals, cancelling internally and externally generated noise from said AC excitation generator appearing as common mode signals at the output of said two separate signal channels, and adding electrical output from said pickoffs appearing as differential mode signals at the output of said two separate signal channels.

8. The method of providing a low noise electronics circuit for use with transducers as in claim 7 wherein detecting said output signals and summing said detected signals comprises receiving the output from one of said pickoffs in one channel, detecting said ouptut to obtain a positive signal, receiving another output signal from the other of said pickoffs in the other of said channels, detecting said other output signal to obtain a negative signal, and summing said positive and negative signals in a resistance network.

9. The method of providing a low noise electronics circuit for use with transducers as in claim 7 wherein detecting said output signals and summing said signals comprises receiving the output from said pickoffs in each channel, detecting said outputs to obtain signals of like polarity, and differencing said signals in a differential amplifier.

10. The method of providing a low noise electronic circuit for use with transducers as in claim 7 together with feeding back common mode signals from said summing means to said AC excitation generator, and amplifying the common mode signals, the amplified common mode feedback operating to reduce common mode oscillations in said AC excitation generator.

11. In a low noise electronic circuit for use with transducers of the type having first and second signal channels, an AC source for exciting first and second pickoffs located in each of said first and second signal channels and producing first and second signals therein, a movable element disposed between said pickoffs, a tuned circuit in each of said first and second signal channels including said first and second pickoffs for increasing said AC source excitation in said pickoffs limited only by the power dissipation characteristics of said pickoffs, means for detecting said first and second signals producing DC signals of predetermined polarity, said detecting means containing electronic circuit elements having no more than two electrical terminals, thereby minimizing injection of asynchronous noise into said channels, and means for combining said DC signals whereby common mode noise signals are cancelled and differential mode output signals are added.

12. A low noise electronic circuit as in claim 11 wherein said detector is configured to produce DC signals of opposite polarity, and wherein said means for combining comprises a summing network for adding said first and second signals, and means for amplifying connected to receive said added differential mode signals.

13. A low noise electronic circuit as in claim 12 wherein said means for amplifying includes means for shaping signal response characteristics.

14. A low noise electronic circuit as in claim 11 wherein said detector is configured to produce DC signals of like polarity, and wherein said means for combining comprises a differential amplifier sensitive to the difference between said first and second signals for providing system output.

15. A low noise electronic circuit as in claim 11 wherein said means for combining provides a common mode sum output, together with a feedback path, means disposed in said feedback path for receiving said summed common mode output and for providing negative feedback coupled to said AC source for reducing common mode level variations in said first and second signal channels.