Comparator-amplifier configuration in an ADC
First Claim
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1. A comparator/amplifier configuration for an analog-to-digital converter (ADC) operating in a sample mode and a conversion mode, comprising:
- a sample capacitor having a first terminal connected to receive at least one analog sample in the sample mode;
a high open loop gain operational amplifier to which a second terminal of said sample capacitor is connected, said operational amplifier configured in the sample mode for operating with a first low gain, substantially lower than said high open loop gain, to drive the second terminal of said sample capacitor to a reference voltage;
a voltage shifter for shifting the voltage on the first terminal of said sample capacitor to the second terminal thereof during said conversion mode and after the sample mode; and
said operational amplifier being reconfigured in the conversion mode to operate at a second gain which is greater than said first low gain and substantially lower than said high open loop gain. for comparing said analog sample amplitude with a reference voltage to determine a relative magnitude thereof.
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Abstract
An analog-to-digital converter amplifier that is configurable with one gain for driving one terminal of a sampling capacitor while the other terminal is sampled to an analog input signal during one time period, and configurable with a different gain for comparing the analog sample with a DAC-generated reference voltage during a second time period.
67 Citations
31 Claims
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1. A comparator/amplifier configuration for an analog-to-digital converter (ADC) operating in a sample mode and a conversion mode, comprising:
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a sample capacitor having a first terminal connected to receive at least one analog sample in the sample mode;
a high open loop gain operational amplifier to which a second terminal of said sample capacitor is connected, said operational amplifier configured in the sample mode for operating with a first low gain, substantially lower than said high open loop gain, to drive the second terminal of said sample capacitor to a reference voltage;
a voltage shifter for shifting the voltage on the first terminal of said sample capacitor to the second terminal thereof during said conversion mode and after the sample mode; and
said operational amplifier being reconfigured in the conversion mode to operate at a second gain which is greater than said first low gain and substantially lower than said high open loop gain. for comparing said analog sample amplitude with a reference voltage to determine a relative magnitude thereof. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19)
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20. A comparator/amplifier configuration for an analog-to-digital converter (ADC), comprising:
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a differential input operational amplifier having a high open loop gain for converting an input analog sample amplitude to a digital signal as a function of a reference voltage;
a feedback network coupled between an input and an output of said operational amplifier; and
a switch arrangement coupled to said feedback network for configuring said operational amplifier for low gain when amplifying said input analog sample amplitude, and for configuring said operational amplifier for a higher gain when operating as a comparator in comparing said input analog sample with said reference voltage. - View Dependent Claims (21, 22, 23, 24, 25, 26)
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27. A method of converting analog sample amplitudes with a comparator/amplifier in an analog-to-digital converter, comprising the steps of:
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amplifying analog sample amplitudes with a first gain during a first time period;
comparing said analog sample amplitudes during a second time period with a reference voltage at a second gain that is higher than said first gain to thereby produce a logic signal;
in response to said logic signal, generating by a SAR a digital word; and
in response to said digital word, generating by a DAC said reference voltage. - View Dependent Claims (28, 29, 30, 31)
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Specification