Coded data generation or conversion – Analog to or from digital conversion – Nonlinear
Reexamination Certificate
2001-11-27
2003-10-14
Wamsley, Patrick (Department: 2819)
Coded data generation or conversion
Analog to or from digital conversion
Nonlinear
C327S350000
Reexamination Certificate
active
06633247
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a logarithmic A/D converter, a logarithmic A/D conversion method, a logarithmic D/A converter, a logarithmic D/A conversion method, and a physical quantity measuring system.
BACKGROUND ART
A logarithmic A/D converter has been used to perform A/D conversion on a detection signal that has a wide dynamic range. This is because a logarithmic A/D converter is capable of providing more sufficient resolution for infinitesimal input than a linear A/D converter, and performing A/D conversion on a higher inputted voltage without becoming saturated. Japanese Laid-Open Patent Application H01-158878 discloses an example of such conventional logarithmic A/D converter.
FIG. 6
is a circuit diagram showing this conventional logarithmic A/D converter. As shown in the figure, a reference voltage “Vref” is applied to a reference voltage terminal
44
of the logarithmic A/D converter, and divided by a plurality of resistors
47
having different resistance so that divided voltages form a progression corresponding to a logarithmic function. Voltage divided by each of the resistors
47
is compared by comparators
42
with an input voltage “Vin” inputted via an analog input terminal
45
. In accordance with a result of this comparison, each of the comparators
42
outputs a logic signal set at either high or low. A decoder
43
converts these logic signals into a digital signal “Dout” represented in binary code, and the converted digital signal “Dout” is outputted from a digital output terminal
46
. In this way, the above conventional A/D converter divides the reference voltage “Vref” by using resistors
47
to produce divided voltages that form the logarithmic function progression, and outputs the digital signal “Dout”.
DISCLOSURE OF INVENTION
A logarithmic A/D converter of the present invention comprises a reference voltage generating unit, a comparison voltage operating unit, and a comparator as described below. The reference voltage generating unit includes at least one first multiplier that raises a predetermine voltage to the nth power to generate a plurality of reference voltages, of which a reference voltage is the nth power of another reference voltage. Based on at least one of the reference voltages, the comparison voltage operating unit generates a comparison voltage. Based on the generated comparison voltage, the comparator generates a digital output value corresponding to a voltage to be converted.
A logarithmic A/D conversion method of the present invention includes the following: generating a plurality of reference voltages, wherein values of the reference voltages have a relation of a progression made by raising the reference voltages to an nth power; generating a plurality of comparison voltages based on at least one of the plurality of reference voltages; and determining an output digital value based on the plurality of comparison voltages. This output digital data corresponds to a voltage to be converted.
A logarithmic D/A converter of the present invention includes a reference voltage generating unit, a selecting unit, and a multiplier. The reference voltage generating unit generates, using a multiplier that raises a predetermined voltage to the nth power, a plurality of reference voltages, of which a reference voltage is the nth power of another reference voltage. Each reference voltage corresponds to a different bit. In accordance with an inputted bit sequence, the selecting unit selects reference voltages. The multiplier performs multiplication using the selected reference voltages to generate an output voltage.
A logarithmic D/A conversion method of the present invention includes the following: raising a predetermined voltage to the nth power to generate reference voltages, of which a reference voltage is the nth power of another reference voltage, and each of which corresponds to a different bit; selecting the reference voltages in accordance with an inputted bit sequence; and performing multiplication using the selected reference voltages to perform D/A conversion.
A physical quantity measuring system according to the present invention includes a logarithmic A/D converter of the present invention.
REFERENCES:
patent: 3646548 (1972-02-01), Van Doren
patent: 4142185 (1979-02-01), Gordon
patent: 5699004 (1997-12-01), Picciotto
patent: 6002122 (1999-12-01), Wolf
patent: S52-134358 (1977-11-01), None
patent: S54-57855 (1979-05-01), None
patent: S58-57132 (1983-04-01), None
patent: 58-057132 (1983-04-01), None
patent: 59-231456 (1984-12-01), None
patent: S61-70439 (1986-05-01), None
patent: 61-70439 (1986-05-01), None
patent: 01-158878 (1989-06-01), None
patent: 02-050523 (1990-02-01), None
Barnes & Thornburg
Sumitomo Metal Industries Ltd.
Wamsley Patrick
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