Patent US3969683A successfully refreshed from Google Patents.
US3969683A
Expired / Lapsed
US
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Automatic level control circuit
Assignee: AT&T Inc
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Filing: 1975-04-21
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Granted: 1976-07-13
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Expires: 1995-04-21
Abstract
Abstract An automatic level control circuit utilizes digital techniques in the gain control loop to maintain an output signal within a predetermined amplitude range. A comparator circuit, which has preselected limits or threshold levels that establish the predetermined amplitude range, produces a hysteresis property in its operation. The hysteresis provides a substantial improvement in noise immunity over conventional automatic gain control circuits. The output of the comparator is applied to digital circuitry which controls the variable gain of a linear amplifier. The digital circuitry also includes a preset circuit which sets the gain of the variable amplifier to the middle of its range, thereby reducing the average time required for an input signal to produce an output signal within the predetermined range. In addition, a decoder indicates the level of the input signal and an out-of-range circuit indicates the relative magnitude of an input signal when it is not within the input range capability of the automatic level control circuit.
Inventors
- 👤 Wayne Nixon Fabricius
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-25 14:21
CPC Classifications
H; H03; H03G; H03G3/00; H03G3/001; H03G3/20; H03G3/30
Claims Analysis
Total Claims: 8
Claim 1
Independent Claim
280 words
An automatic signal level control circuit comprising: amplifying means connected to receive an input signal and having variable gain that changes in precisely defined discrete increments to provide an output signal whose magnitude is variable independent of the level of the input signal, comparing means having an upper predetermined limit and a lower predetermined limit for evaluating the amplitude of said output signal, said comparing means having feedback means to provide hysteresis in its transfer characteristic, and said comparing means producing an output signal indicative of the amplitude of said output signal relative to said limits as the hysteresis in the transfer characteristic therein provides substantial noise immunity in the indication of said output signal of said comparing means from the significant amount of noise that may be present on said output signal when it passes through one of said limits, digital means for controlling the gain of said amplifying means comprising logic means and up/down counting means, said logic means responsive to the output of said comparing means, said counting means being enabled and inhibited by said logic means, and said counting means having counting states and associated outputs that control the gain of said amplifying means to maintain its output between said limits, and decoding means responsive to the associated outputs of said counting means for providing a set of digital signals indicative of the level of the input signal being received by said amplifying means, said decoding means comprising read-only memory means, inverting means, gating means connected to the output of said counting means, and switching means for applying ground potential to said read-only memory means and said gating means to produce the set of digital signals.
Claim 2
Dependent Claim
280 words
An automatic signal level control circuit comprising: amplifying means connected to receive an input signal and having variable gain that changes in precisely defined discrete increments to provide an output signal whose magnitude is variable independent of the level of the input signal, comparing means having an upper predetermined limit and a lower predetermined limit for evaluating the amplitude of said output signal, said comparing means having feedback means to provide hysteresis in its transfer characteristic, and said comparing means producing an output signal indicative of the amplitude of said output signal relative to said limits as the hysteresis in the transfer characteristic therein provides substantial noise immunity in the indication of said output signal of said comparing means from the significant amount of noise that may be present on said output signal when it passes through one of said limits, digital means for controlling the gain of said amplifying means comprising logic means and up/down counting means, said logic means responsive to the output of said comparing means, said counting means being enabled and inhibited by said logic means, and said counting means having counting states and associated outputs that control the gain of said amplifying means to maintain its output between said limits, and decoding means responsive to the associated outputs of said counting means for providing a set of digital signals indicative of the level of the input signal being received by said amplifying means, said decoding means comprising read-only memory means, inverting means, gating means connected to the output of said counting means, and switching means for applying ground potential to said read-only memory means and said gating means to produce the set of digital signals.
Claim 3
Dependent Claim
123 words
An automatic signal level control circuit in accordance with claim 1 wherein said comparing means comprises two differential operational amplifiers, each having one input referenced to one of said predetermined limits, means for applying said output signal to the other input of each of said differential amplifiers, said feedback means including a resistive means for providing positive feedback to each of said differential amplifiers, and output means in circuit with one of said differential amplifiers providing a first signal indicative of the relative position of the amplitude of said output signal with respect to one of said limits and second output means in response to the output of both of said differential amplifiers for indicating when said output signal is between said limits.
Claim 4
Dependent Claim
69 words
An automatic signal level control circuit in accordance with claim 2 wherein said amplifier means comprises a variable attenuator and an amplifier serially connected in cascade, said variable attenuator comprising a plurality of stages serially cascaded to provide selected quantities of attenuation in accordance with the output of said counting means, and said decoding means indicates the level of the input signal received by said amplifying means in decibels.
Claim 5
Dependent Claim
60 words
An automatic signal level control circuit in accordance with claim 3 further comprising detecting means connected between the output of said amplifying means, and the input of said comparing means for supplying an input signal proportional to the magnitude of the output signal from said amplifier means so that said comparing means evaluates the absolute level of the output signal.
Claim 6
Dependent Claim
61 words
An automatic signal level control circuit in accordance with claim 4 wherein said digital means further comprises clocking means for determining the counting rate of said counting means, and said logic means detects the states of said counting means indicative of a minimum value and a maximum value and inhibits said clocking means from changing the state of said counting means.
Claim 7
Dependent Claim
83 words
An automatic signal level control circuit in accordance with claim 5 further comprising presetting means connected to said logic means for indicating when an input signal is first applied to said amplifying means and said presetting means supplying an output pulse of a predetermined duration which serves to set said counting means at a preselected state in its count so as to reduce the average time which elapses before the output of said detecting means is between the thresholds of said comparing means.
Claim 8
Dependent Claim
102 words
An automatic signal level control circuit in accordance with claim 6 further comprising evaluating means connected to said logic means and said decoding means, said evaluating means comprising gating means which produce outputs indicative of two signaling conditions at the input of said signal level control circuit, the first condition being when magnitude of the input signal applied to said amplifying means is insufficient to satisfy the lower limit of said comparing means and the second condition being when the magnitude of the input signal of said level control circuit produces a signal at said comparing means exceeding the upper limit therein.
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) | 1979-07-13 | 1980-01-12 | 1980-07-13 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1983-07-13 | 1984-01-12 | 1984-07-13 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1987-07-13 | 1988-01-12 | 1988-07-13 | $7700.00 | Window Closed / Lapsed |