Coded data generation or conversion – Analog to or from digital conversion – Analog to digital conversion
Reexamination Certificate
1999-05-27
2001-01-09
Young, Brian (Department: 2819)
Coded data generation or conversion
Analog to or from digital conversion
Analog to digital conversion
Reexamination Certificate
active
06172635
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an analog-to-digital (A/D) converter which eliminates the need for accurate components but provides high conversion accuracy even when an analog signal input thereto is at a low level.
FIG. 1
schematically illustrates A/D conversion processing which has been conventionally performed in a variety of applications. An input analog signal is converted to a digital signal by an A/D converter having a resolution of N bits. In this event, the accuracy of the A/D conversion is determined by the number of bits N of the used A/D converter.
With the illustrated configuration, however, since only one A/D converter is used, the dynamic range is determined by the accuracy of the A/D converter. Therefore, a sufficient dynamic range cannot be ensured if an A/D converter with a low accuracy is used. On the contrary, when an accurate A/D converter is employed for ensuring a sufficient dynamic range, the cost of the entire apparatus is increased due to a high cost of the A/D converter itself.
In addition, in the A/D conversion processing illustrated in
FIG. 1
, noise produced by the A/D converter itself is often larger than quantization noise which is determined by the resolution of N bits. The noise produced by the A/D converter itself causes a higher noise floor, thereby degrading the dynamic range in consequence.
SUMMARY OF THE INVENTION
The present invention has been made to solve the problems mentioned above, and its object is to provide an A/D converter which is capable of performing highly accurate A/D conversion even with A/D conversion units of low accuracy, and capable of reducing a noise floor and thus improving the dynamic range.
To achieve the above object, the present invention provides an A/D converter which comprises:
a first line including a first A/D conversion unit connected to an input terminal applied with an analog signal;
a second line including a first amplifier connected to the input terminal and having an amplification ratio of 2
m
, where m>0, a second A/D conversion unit connected to an output of the first amplifier, and a second amplifier connected to an output of the second A/D conversion unit and having an amplification ratio of 2
−m
; and
switching means for connecting either an output of the first line or an output of the second line to an output terminal in accordance with an output level of the first line.
The switching means may connect the output terminal to the output of the first line when the output level of the first line exceeds a predetermined switching level, and connect the output terminal to the output of the second line when the output level of the first line is below the predetermined switching level.
The switching means preferably has a cross fade characteristic for switching one of the first and second lines to the other such that the switching means gradually decreases an output level of the one line while it gradually increases an output level of the other line for a predetermined time period at the output terminal, and delivers an output of the other line from the output terminal after the lapse of the predetermined time period.
Also, the switching means preferably has a hysteresis characteristic having a first switching level for switching the output terminal from the output of the first line to the output of the second line, and a second switching level for switching the output terminal from the output of the second line to the output of the first line, where the second switching level is higher than the first switching level.
The A/D converter may further comprise at least one additional line comprising an amplifier connected to the input terminal and having an amplification ratio of 2
k
, where k>0 and k≠m, an A/D conversion unit connected to an output of the amplifier, and another amplifier connected to an output of the A/D conversion unit and having an amplification ratio of 2
−k
, such that the switching means connects the output terminal to either of outputs of the at least three lines connected to the switching means in accordance with the output level of the first line.
REFERENCES:
patent: 4940982 (1990-07-01), Gulczynski
patent: 4985702 (1991-01-01), Penney
Nakamura Shoji
Yoshikawa Takashi
TOA Corporation
Townsend and Townsend / and Crew LLP
Young Brian
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