Coded data generation or conversion – Analog to or from digital conversion – Analog to digital conversion
Reexamination Certificate
1999-03-18
2001-08-28
Young, Brian (Department: 2819)
Coded data generation or conversion
Analog to or from digital conversion
Analog to digital conversion
C341S156000
Reexamination Certificate
active
06281828
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Filed of the Invention
The present invention relates to an analog/digital (A/D) converter apparatus and, more particularly, to an analog/digital converter apparatus having a high-precision A/D conversion function which is performed in consideration of an influence of device mismatch caused by manufacturing a semiconductor integrated circuit.
2. Discussion of the Background
The advance of manufacturing technology of semiconductor integrated circuits has enabled a high-speed processor to be manufactured inexpensively. Such a processor has recently been incorporated into household electrical appliances and communications equipment to process a number of signals in digital form. It is thought that digital signal processing will be advanced from now on and its share will be increased even in the field of communications system. To achieve sophisticated signal processing, a processing apparatus has to be operated with high precision as well as at high speed. In systems of such a field, an analog signal is used to receive a signal or to interface with the outside. A low-cost, high-speed and high-precision analog/digital converter apparatus is therefore required in order to spread digital signal processing more and more in the future.
A representative example of an analog/digital converter apparatus is a flash type analog/digital converter apparatus for comparing the level of an input analog signal with that of a reference signal and converting it into a digital signal. This type of converter apparatus executes simple processing of comparing an input signal with plural reference signals at once and is therefore suited to an application area requiring high-speed processing. Factors for determining conversion precision of the flash type analog/digital converter apparatus are equivalent input offset of a comparator section for determining a relationship in voltage level between an input analog signal and a reference signal and resolution of a reference voltage generator. When an analog/digital converter apparatus is realized in a semiconductor integrated circuit, both the factors of equivalent input offset and resolution are due to device mismatch caused by manufacturing the semiconductor integrated circuit. Since, at this point in time, the equivalent input offset is more remarkable as a factor for determining the above conversion precision than mismatch of elements constituting the reference voltage generator, the conversion precision depends upon the equivalent input offset.
A prior art analog/digital converter apparatus adopts a method of relaxing an influence of equivalent input offset of a comparator. In this apparatus, for example, an analog input voltage and a reference voltage are not compared directly, but an output of a differential amplifier receiving both a reference voltage and an analog input voltage is added to outputs of a plurality of differential amplifiers adjacent thereto and a result of this addition is compared with the above output of the differential amplifier (disclosed in Kaneko et al., “A/D CONVERTER,” Jpn. Pat. Appln. KOKAI Publication No. 6-350452). The equivalent input offset can thus be averaged by the number of added outputs of the differential amplifiers.
In the above method, however, the number of outputs used for averaging the equivalent input offset is two or three and thus an influence of device mismatch still remains.
Furthermore, an adder circuit with considerable precision is needed to add output signals of the plural differential amplifiers, as is time required for processing them. In other words, it is understood that a great improvement in conversion precision cannot be expected though additional processing is given to a system for processing a plurality of signals at once.
Even though a problem of equivalent input offset of comparators is resolved, precision is still restricted by mismatch of elements constituting a reference voltage generator.
Therefore, unless the problems of both equivalent input offset and device mismatch are overcome fundamentally, a high-precision analog/digital converter apparatus is very difficult to achieve.
If, as described above, an analog/digital converter apparatus is constituted of a semiconductor integrated circuit, it causes a problem of device mismatch and it is difficult to achieve at low cost and with high conversion precision.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an analog/digital converter apparatus which resolves problems of both equivalent input offset of comparators caused by device mismatch and mismatch of elements constituting a reference voltage generator, and which decreases in costs and increases in precision.
According to a first aspect of the present invention, there is provided an analog/digital converter apparatus comprising a reference signal generator section which generates a reference signal, a comparator section which determines a relationship in level between an input analog signal and the reference signal, and an encoder which converts a comparison result of the comparator into a digital signal. The comparator section includes a comparator which compares the input analog signal with the reference signal and a signal switching section which switches a signal line between the comparator and each of an input section which receives the analog signal and the reference signal generator section.
The comparator section further includes a differential amplifier connected to the signal switching section, an analog signal holding section which holds an analog signal output from the differential amplifier, a sign inverter section which inverts a sign of the analog signal, and an adder section which adds an inverted analog signal and the analog signal output from the differential amplifier and supplies an addition result to the comparator.
According to a second aspect of the present invention, there is provided an analog/digital converter apparatus comprising a reference signal generator section constituted by arranging a plurality of reference elements, for generating a reference signal, a switching section which switches a pattern of connection of the reference elements to a plurality of output lines, a comparator section which determines a relationship in level between an input analog signal and the reference signal, and an encoder which converts a comparison result of each of the comparator sections into a digital signal.
According to a third aspect of the present invention, there is provided an analog/digital converter apparatus comprising a reference signal generator section which generates a reference signal, a comparator section which determines a relationship in level between an input analog signal and the reference signal, and an encoder which converts a comparison result of the comparator section into a digital signal. The reference signal generator section includes a plurality of reference elements constituted of passive elements or active elements, a group of switching elements arranged in matrix, and a switching section which switches a connection pattern of the switching elements. The comparator section includes a comparator which determines a relationship in level between the input analog signal and the reference signal and an averaging unit succeeding the comparator, for averaging a plurality of compared signals generated by switching the connection pattern of the reference elements.
According to a fourth aspect of the present invention, there is provided an analog/digital converter apparatus comprising a reference signal generator section including a plurality of reference elements constituted of passive elements or active elements and a group of switching elements connected to the reference elements and arranged in matrix, the reference signal generator section generating a reference signal, a comparator section which determines a relationship in level between an input analog signal and the reference signal, an encoder which converts a comparison result of the comparator section into a digital signal, and an averag
Kimura Tomohisa
Yasuda Akira
Kabushiki Kaisha Toshiba
Nguyen John
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Young Brian
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