Logarithmic circuit with wide dynamic range
US4091329A · kind A · utility
Inventors
Key dates
| Filing date | Feb 16, 1977 |
| Grant date | May 23, 1978 |
| Priority date | — |
| Expiry date | Feb 16, 1997 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG06G7/24
- WIPO fieldComputer technology
- WIPO sectorElectrical engineering
Abstract
A circuit deriving an output voltage that is proportional to the logarithm of a DC input voltage susceptible to wide variations in amplitude includes a constant current source which forward biases a diode so that the diode operates in the exponential portion of its voltage versus current characteristic, above its saturation current. The constant current source includes first and second, cascaded feedback, DC operational amplifiers connected in a negative feedback circuit. An input terminal of the first amplifier is responsive to the input voltage. A circuit shunting the first amplifier output terminal includes a resistor in series with the diode. The voltage across the resistor is sensed at the input of the second DC operational feedback amplifier. The feedback voltage derived from the output of the second amplifier is subtracted by the first amplifier from the input voltage so that the current flowing through the resistor is proportional to the input voltage over the wide range of variations in amplitude of the input voltage.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.