Successive type analog-to-digital converter with a variable reference voltage for the digital to analog converter
First Claim
1. An A/D converter for converting an analog input voltage into a digital output signal, comprising:
- comparator means for comparing the analog input voltage and an analog comparison voltage to output the digital output signal;
D/A converter means for generating the analog comparison voltage in response to a reference voltage and a first digital signal;
first register means for storing the digital output signal and for providing the first digital signal;
reference voltage generator means for generating the reference voltage by changing a predetermined voltage in response to a second digital signal; and
second register means for storing the second digital signal, wherein before said analog comparison voltage becomes lower than the analog input voltage for a first time after the A/D conversion starts, the second digital signal is changed in response to a first clock signal so as to decrease the reference voltage, and the first digital signal output from said first register means is not changed; and
after the analog comparison voltage becomes lower than the analog input voltage for the first time after the A/D conversion starts, the second digital signal is not changed so that the reference voltage is held constant, and the first digital signal is changed in response to a second clock signal and the digital output signal from said comparator so as to change the analog comparison voltage.
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Abstract
A successive approximation analog to digital converter is provided with a variable reference voltage. A comparator compares an analog input voltage and an analog comparison voltage to obtain a digital output signal. Before the analog comparison voltage becomes lower than the analog input voltage, the first time after the analog to digital conversion starts, the second digital signal is changed in response to a first clock signal to decrease the reference voltage so that the first digital signal output form the first register is not changed. After the analog comparison voltage becomes lower than the analog input voltage the first time after the analog to digital conversion starts, the second digital signal is not changed so that the reference voltage is kept constant. The first digital signal is then changed in response to a second clock signal and the digital output signal to change the analog comparison voltage, whereby the bit member of the digital-to-analog converter is reduced.
29 Citations
19 Claims
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1. An A/D converter for converting an analog input voltage into a digital output signal, comprising:
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comparator means for comparing the analog input voltage and an analog comparison voltage to output the digital output signal; D/A converter means for generating the analog comparison voltage in response to a reference voltage and a first digital signal; first register means for storing the digital output signal and for providing the first digital signal; reference voltage generator means for generating the reference voltage by changing a predetermined voltage in response to a second digital signal; and second register means for storing the second digital signal, wherein before said analog comparison voltage becomes lower than the analog input voltage for a first time after the A/D conversion starts, the second digital signal is changed in response to a first clock signal so as to decrease the reference voltage, and the first digital signal output from said first register means is not changed; and
after the analog comparison voltage becomes lower than the analog input voltage for the first time after the A/D conversion starts, the second digital signal is not changed so that the reference voltage is held constant, and the first digital signal is changed in response to a second clock signal and the digital output signal from said comparator so as to change the analog comparison voltage. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
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18. A method of analog to digital conversion of an analog input voltage to a digital output signal comprising the steps of:
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(a) determining the digital output signal by comparing the analog input voltage with an analog comparison voltage; (b) varying a reference voltage by decreasing the reference voltage until the analog comparison voltage becomes lower than the analog input voltage for a first time; (c) determining the analog comparison voltage by digital to analog conversion based on the reference voltage until the analog comparison voltage becomes lower than the analog input voltage for the first time; and (d) determining the analog comparison voltage by digital to analog conversion of a value indicative of the digital output signal after the analog comparison voltage becomes lower than the analog input voltage for the first time.
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19. An apparatus for analog to digital conversion of an analog input voltage to a digital output signal comprising:
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(a) first means for determining the digital output signal by comparing the analog input voltage with an analog comparison voltage; (b) second means for varying a reference voltage by decreasing the reference voltage until the analog comparison voltage becomes lower than the analog input voltage for a first time; (c) third means for determining the analog comparison voltage by digital to analog conversion based on the reference voltage until the analog comparison voltage becomes lower than the analog input voltage for the first time; and (d) fourth means for determining the analog comparison voltage by digital to analog conversion of a value indicative of the digital output signal after the analog comparison voltage becomes lower than the analog input voltage for the first time.
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Specification