US3679975A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Resistive modulator
Assignee: Individual
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Filing: 1970-08-06
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Granted: 1972-07-25
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Expires: 1990-08-06
Abstract
Abstract Circuitry for sensing applied potentials, the circuitry presenting a high impedance to the source of the potentials to be sensed, is disclosed. The invention employs a matched pair of field effect transistors which are operated in accordance with a resistive modulation technique. In the disclosed embodiment the transistors are connected in opposite legs of a balanced bridge circuit and are excited by alternating the current, input signals applied to the gate of one of the transistors producing a small change in the resistance of that transistor.
Inventors
- 👤 Harry Fein
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-30 19:37
CPC Classifications
G; G01; G01R; G01R19/00; G01R19/18
Claims Analysis
Total Claims: 4
Claim 1
Independent Claim
196 words
A voltage responsive device characterized by a high input impedance, said device comprising: modulator means comprising an initially balanced bridge circuit including a pair of matched resistors in opposite legs, said bridge circuit further including first and second field effect transistors in opposite legs; means for applying an alternating excitation voltage across said bridge circuit, the amplitude of said excitation voltage being selected so as to bias said field effect transistors for operation as resistance modulators; means for applying a direct current input signal to the gate electrode of said first field effect transistor to thereby vary the resistance of said first transistor; differential amplifier means connected to said modulator means for receiving and amPlifying alternating potentials commensurate with the unbalancing of said bridge circuit resulting from variations in the effective resistance of said first transistor; detector means; means applying the output of said differential amplifier means to said detector means whereby said detector means will provide a direct current output voltage commensurate with the magnitude of the input signal; and means for feeding a portion of said direct current output voltage back to said bridge circuit to maintain said bridge circuit in a balanced condition.
Claim 2
Dependent Claim
196 words
A voltage responsive device characterized by a high input impedance, said device comprising: modulator means comprising an initially balanced bridge circuit including a pair of matched resistors in opposite legs, said bridge circuit further including first and second field effect transistors in opposite legs; means for applying an alternating excitation voltage across said bridge circuit, the amplitude of said excitation voltage being selected so as to bias said field effect transistors for operation as resistance modulators; means for applying a direct current input signal to the gate electrode of said first field effect transistor to thereby vary the resistance of said first transistor; differential amplifier means connected to said modulator means for receiving and amPlifying alternating potentials commensurate with the unbalancing of said bridge circuit resulting from variations in the effective resistance of said first transistor; detector means; means applying the output of said differential amplifier means to said detector means whereby said detector means will provide a direct current output voltage commensurate with the magnitude of the input signal; and means for feeding a portion of said direct current output voltage back to said bridge circuit to maintain said bridge circuit in a balanced condition.
Claim 3
Dependent Claim
36 words
The apparatus of claim 1 wherein said detector means comprises: a synchronous detector; and means for applying an A.C. reference signal to said detector from said means for applying an excitation current to said modulator means.
Claim 4
Dependent Claim
82 words
The apparatus of claim 2 wherein said means for feeding back a portion of the output voltage comprises: direct current amplifier means connected to receive the output of said detector means, said direct current amplifier means functioning as an impedance buffer; voltage divider means connected to the output terminal of said direct current amplifier means; and means connecting an intermediate point of said voltage divider to the common point of said bridge circuit which is connected to said first and second transistors.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1975-07-25 | 1976-01-24 | 1976-07-25 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1979-07-25 | 1980-01-24 | 1980-07-25 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1983-07-25 | 1984-01-24 | 1984-07-25 | $7700.00 | Window Closed / Lapsed |