US3811088A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Logarithmic converter
Assignee: Hekimian Laboratories Inc
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Filing: 1972-10-19
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Granted: 1974-05-14
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Expires: 1992-10-19
Abstract
Abstract A logarighmic converter circuit includes an operational amplifier to which an input signal and a reference signal are alternately applied during respective half-cycles of a gating signal. During the input signal half-cycle, the amplifier output signal charges a capacitor through a diode and cuts off an output gate in a meter circuit, the capacitor voltage is degeneratively fed back to the amplifier. During the reference signal half cycle, the amplifier circuit signal reverses polarity, reversebiasing the diode and closing the output circuit gate, until the capacitor discharges to the reference level. Current flows in the meter circuit only during the capacitor discharge interval which is proportional to the logarithm of the input signal amplitude. The meter movement integrates the current duty cycle to provide a reading of the signal logarithm. The output current may also serve as a gate for a counter fed by timing pulses or for a digital voltmeter to provide a digital output indication.
Inventors
- 👤 N Hekimian
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-26 11:28
CPC Classifications
G; G06; G06G; G06G7/00; G06G7/12; G06G7/24; G01; G01R; G01R15/00; G01R15/005
Claims Analysis
Total Claims: 15
Claim 1
Independent Claim
356 words
A logarithmic converter circuit for providing an indication of the logarithm of the amplitude of an input voltage signal, said circuit comprising: an operational amplifier including inverting and non-inverting input terminals and an output terminal, wherein the voltage at said output terminal is of one polarity when the voltage at one of said input terminals exceeds the voltage at the other of said input terminals, and is of opposite polarity when the voltage at said other input terminal exceeds the voltage at said one input terminal; a source of gating signal of constant frequency and which alternates between first and second gating levels during first and second cycle portions, respectively; means for providing a D.C. reference voltage which is smaller in magnitude than the peak voltage of said input signal; input gating means responsive to said gating signal for rendering the voltage at said one input terminal of said operational amplifier equal to the input voltage during said first cycle portion of said gating signal and equal to said reference voltage during said second cycle portion of said gating signal; a storage capacitor; feedback means for applying the voltage appearing across said storage capacitor to said other of said input terminals of said operational amplifier; further gating means responsive to the voltage at said output terminal having said one polarity for coupling said storage capacitor to said output terminal in charging relationship, and responsive to the voltage at said output terminal having said second polarity for decoupling said storage capacitor from said output terminal; a discharge path connected to permit exponential decay of the voltage across said storage capacitor when said storage capacitor is decoupled from said output terminal, said discharge path and said capacitor having a time constant which is sufficiently short to permit the voltage across said storage capacitor to discharge from the peak voltage of said input signal to said reference voltage within a half-cycle of said gating signal; and output means responsive to said voltage at said output terminal having said second polarity for providing an indication which varies in proportion to the logarithm of the peak voltage of said input signal.
Claim 2
Dependent Claim
356 words
A logarithmic converter circuit for providing an indication of the logarithm of the amplitude of an input voltage signal, said circuit comprising: an operational amplifier including inverting and non-inverting input terminals and an output terminal, wherein the voltage at said output terminal is of one polarity when the voltage at one of said input terminals exceeds the voltage at the other of said input terminals, and is of opposite polarity when the voltage at said other input terminal exceeds the voltage at said one input terminal; a source of gating signal of constant frequency and which alternates between first and second gating levels during first and second cycle portions, respectively; means for providing a D.C. reference voltage which is smaller in magnitude than the peak voltage of said input signal; input gating means responsive to said gating signal for rendering the voltage at said one input terminal of said operational amplifier equal to the input voltage during said first cycle portion of said gating signal and equal to said reference voltage during said second cycle portion of said gating signal; a storage capacitor; feedback means for applying the voltage appearing across said storage capacitor to said other of said input terminals of said operational amplifier; further gating means responsive to the voltage at said output terminal having said one polarity for coupling said storage capacitor to said output terminal in charging relationship, and responsive to the voltage at said output terminal having said second polarity for decoupling said storage capacitor from said output terminal; a discharge path connected to permit exponential decay of the voltage across said storage capacitor when said storage capacitor is decoupled from said output terminal, said discharge path and said capacitor having a time constant which is sufficiently short to permit the voltage across said storage capacitor to discharge from the peak voltage of said input signal to said reference voltage within a half-cycle of said gating signal; and output means responsive to said voltage at said output terminal having said second polarity for providing an indication which varies in proportion to the logarithm of the peak voltage of said input signal.
Claim 3
Dependent Claim
70 words
The circuit according to claim 1 wherein said output means comprises: a source of supply voltage; a meter; and output gating means actuable in response to the voltage at said output terminal having said second polarity for providing a current path for said source of supply voltage through said meter; wherein said meter includes a meter movement which has a slow response relative to the frequency of said gating signal.
Claim 4
Dependent Claim
75 words
The circuit according to claim 1 wherein said output means inCludes: a gated binary counter; a source of clock pulses having a substantially higher frequency than said gating signal; and means for applying said clock pulses to said binary counter; and output gating means responsive to the voltage at said output terminal of said operational amplifier having said second polarity for gating said binary counter into a counting mode wherein said clock pulses are counted.
Claim 5
Dependent Claim
41 words
The circuit according to claim 1 wherein said further gating means comprises a diode connected to pass current between said storage capacitor and said output terminal of said operational amplifier when the voltage at said output terminal has said one polarity.
Claim 6
Dependent Claim
44 words
The circuit according to claim 1 wherein said input gating means comprises a transistor having a collector coupled to said one input terminal of said operational amplifier, an emitter coupled to said reference voltage, and a base coupled to said source of gating signal.
Claim 7
Dependent Claim
30 words
The circuit according to claim 1 wherein said feedback means comprises a second operational amplifier connected for applying the voltage from across said storage capacitor to said other input terminal.
Claim 8
Dependent Claim
18 words
The circuit according to claim 1 further comprising means for selectively adjusting the level of said reference voltage.
Claim 9
Dependent Claim
28 words
The circuit according to claim 1 wherein said one input terminal corresponds to said non-inverting input terminal and said other input terminal corresponds to said inverting input terminal.
Claim 10
Dependent Claim
240 words
A logarithmic converter circuit for providing an output signal having a parameter proportional to the logarithm of the amplitude of an input voltage, said circuit comprising: first and second operational amplifiers, each having first and second input terminals of opposite polarity and an output terminal; means for coupling the output terminal of said second operational amplifier to the second input terminals of said first and second operational amplifier; means for providing a reference voltage; gating means for successively and alternately rendering the voltage at said first input terminal of said first operational amplifier equal to said input and reference voltages; a charging capacitor and discharge resistance connected in parallel and to the first input terminal of said second operational amplifier; a diode connected in series between the output terminal of said first operational amplifier and the first input terminal of said second operational amplifier, said diode being poled to conduct current flow between the output terminal of said first operational amplifier and said capacitor when the voltage at said output terminal of said first operational amplifier is of greater magnitude than the voltage across said capacitor, and to decouple said capacitor from the output terminal of said first operational amplifier when the voltage across said capacitor if of greater magnitude than the voltage at the output terminal of said first operational amplifier; and output means connected to the output terminal of said first operational amplifier for providing said output signal.
Claim 11
Dependent Claim
240 words
A logarithmic converter circuit for providing an output signal having a parameter proportional to the logarithm of the amplitude of an input voltage, said circuit comprising: first and second operational amplifiers, each having first and second input terminals of opposite polarity and an output terminal; means for coupling the output terminal of said second operational amplifier to the second input terminals of said first and second operational amplifier; means for providing a reference voltage; gating means for successively and alternately rendering the voltage at said first input terminal of said first operational amplifier equal to said input and reference voltages; a charging capacitor and discharge resistance connected in parallel and to the first input terminal of said second operational amplifier; a diode connected in series between the output terminal of said first operational amplifier and the first input terminal of said second operational amplifier, said diode being poled to conduct current flow between the output terminal of said first operational amplifier and said capacitor when the voltage at said output terminal of said first operational amplifier is of greater magnitude than the voltage across said capacitor, and to decouple said capacitor from the output terminal of said first operational amplifier when the voltage across said capacitor if of greater magnitude than the voltage at the output terminal of said first operational amplifier; and output means connected to the output terminal of said first operational amplifier for providing said output signal.
Claim 12
Dependent Claim
52 words
The circuit according to claim 9 wherein said output means comprises means for providing an indication proportional to the logarithm of the amplitude of said input signal in response to time interval required for the voltage across said capacitor to discharge from the amplitude of said input signal to said reference voltage.
Claim 13
Dependent Claim
71 words
The circuit according to claim 9 wherein said output means comprises means operative when the voltage at said first input terminal of said first operational amplifier is rendered equal to said reference voltage for providing an output signal when the magnitude of the voltage at said second input terminal of said first operational amplifier is greater than the magnitude of the voltage at said output terminal of said first operational amplifier.
Claim 14
Dependent Claim
228 words
A logarithmic converter circuit comprising: an operational amplifier of the differential tYpe having first and second input terminals and an output terminal at which is provided an amplified voltage proportional in amplitude and polarity to the difference voltage across said first and second input terminals; a source of input voltage; a source of reference voltage; gating means for alternately rendering the voltage at said first input terminal equal to said input voltage and said reference voltage; a capacitor and resistor connected in parallel; feedback means for applying to said second input terminal a voltage proportional to the voltage across said capacitor; gating means for coupling said output terminal to said parallel-connected resistor and capacitor when the voltage at said output terminal is of greater magnitude than the voltage across said capacitor and for decoupling said resistor and capacitor from said output terminal when the voltage across said capacitor is of greater magnitude than the voltage at said output terminal; whereby the voltage across said capacitor is discharged through said resistor when said resistor and capacitor are decoupled from said output terminal by said gating means but tends to follow the voltage at said output terminal when said resistor and capacitor are coupled to said output terminal; and whereby the duty cycle of said gating means represents a measure of the logarithm of the amplitude of said input voltage.
Claim 15
Dependent Claim
228 words
A logarithmic converter circuit comprising: an operational amplifier of the differential tYpe having first and second input terminals and an output terminal at which is provided an amplified voltage proportional in amplitude and polarity to the difference voltage across said first and second input terminals; a source of input voltage; a source of reference voltage; gating means for alternately rendering the voltage at said first input terminal equal to said input voltage and said reference voltage; a capacitor and resistor connected in parallel; feedback means for applying to said second input terminal a voltage proportional to the voltage across said capacitor; gating means for coupling said output terminal to said parallel-connected resistor and capacitor when the voltage at said output terminal is of greater magnitude than the voltage across said capacitor and for decoupling said resistor and capacitor from said output terminal when the voltage across said capacitor is of greater magnitude than the voltage at said output terminal; whereby the voltage across said capacitor is discharged through said resistor when said resistor and capacitor are decoupled from said output terminal by said gating means but tends to follow the voltage at said output terminal when said resistor and capacitor are coupled to said output terminal; and whereby the duty cycle of said gating means represents a measure of the logarithm of the amplitude of said input voltage.
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) | 1977-05-13 | 1977-11-12 | 1978-05-14 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-05-13 | 1981-11-12 | 1982-05-14 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-05-13 | 1985-11-12 | 1986-05-14 | $7700.00 | Window Closed / Lapsed |