Low-noise, low-power, low drift offset correction in operational and instrumentation amplifiers
First Claim
Patent Images
1. In an amplifier system, a circuit comprising:
- a first differential amplifier;
first and second choppers for chopping the input and the output of the first differential amplifier, respectively;
autozero circuitry coupled to the first differential amplifier for autozeroing the first differential amplifier;
the autozero circuitry operating at a first frequency and the choppers operating at a second frequency, the first frequency being twice the second frequency, the second frequency having a 50% duty cycle;
the first frequency having a duty cycle of less than 50%;
each half cycle of the choppers being interrupted while the first differential amplifier is auto-zeroed.
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Abstract
Low-noise, low-power, low drift offset correction in operational and instrumentation amplifiers and amplifiers using the same are disclosed. The amplifiers disclosed use different combinations of chopping and auto-zero techniques. Also disclosed are amplifiers using on-off switches to affect the chopping and auto-zeroing, with unique circuits for driving the switches on the differential input to provide boot-strapped switch controls. Other features are disclosed.
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Citations
28 Claims
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1. In an amplifier system, a circuit comprising:
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a first differential amplifier; first and second choppers for chopping the input and the output of the first differential amplifier, respectively; autozero circuitry coupled to the first differential amplifier for autozeroing the first differential amplifier; the autozero circuitry operating at a first frequency and the choppers operating at a second frequency, the first frequency being twice the second frequency, the second frequency having a 50% duty cycle; the first frequency having a duty cycle of less than 50%; each half cycle of the choppers being interrupted while the first differential amplifier is auto-zeroed. - View Dependent Claims (2, 3)
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4. In an amplifier system, a circuit comprising:
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a first differential amplifier; first and second choppers for chopping the input and the output of the first differential amplifier, respectively; the first chopper being coupled to the first and second differential inputs of the amplifier system; a first-switch having a first first-switch state coupling the differential inputs of the first differential amplifier to differential outputs of the first chopper, and a second first-switch state connecting the differential inputs of the first differential amplifier together; a second differential amplifier, the second differential amplifier having differential inputs, each connected to a circuit ground through a respective capacitance; differential outputs of the first and second differential amplifiers being coupled in common; an output amplifier having an input coupled to an output of the second chopper; a second-switch having a first second-switch state coupling the common outputs of the first and second differential amplifiers to an input of the second chopper, and a second second-switch state coupling the common outputs of the first and second differential amplifiers to the differential inputs of the second differential amplifier; the first and second switches operating at a first frequency and the choppers operating at a second frequency unequal to the first frequency. - View Dependent Claims (5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20)
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21. A method of operating a chopper stabilized first amplifier, the chopper stabilized first amplifier having an auto-zeroing capability comprising:
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operating the chopper stabilization at a first frequency; and
,operating the auto-zeroing at a second frequency; the ratio of the frequencies being two to one; the second frequency being twice the first frequency and having a duty cycle of less than one half.
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22. A method of operating a chopper stabilized first amplifier, the chopper stabilized first amplifier having an auto-zeroing capability comprising:
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operating the chopper stabilization at a first frequency; and
,operating the auto-zeroing at a second frequency; the ratio of the frequencies being two to one; the second frequency having a duty cycle of not more than one-quarter.
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23. A method of operating a chopper stabilized first amplifier, the chopper stabilized first amplifier having an auto-zeroing capability comprising:
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operating the chopper stabilization at a first frequency; and
,operating the auto-zeroing at a second frequency; the ratio of the frequencies being two to one; after each cycle of the chopper stabilization of the first amplifier, chopper stabilizing a second amplifier using the same choppers; auto-zeroing the second amplifier while the first amplifier is being chopper stabilized; and
,auto-zeroing the first amplifier while the second amplifier is being chopper stabilized; the outputs of the first and second amplifiers being connected in common.
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24. A method of operating a chopper stabilized first amplifier, the chopper stabilized first amplifier having an auto-zeroing capability wherein the chopper stabilized first amplifier has first, second and third pluralities of open and closed switches, the first and second switches being coupled as input and output chopper switches and the third switches being coupled as auto-zero switches, wherein the first switches are all closed at the same time, but not when the second and third switches are closed, the second switches are all closed at the same time, but not when any of the first and third switches are closed, and the third switches are all closed at the same time, but not when the first or second switches are closed, whereby the switch operation is nonoverlapping, the third switches being closed at a first frequency with a duty cycle of less than 50%, the first switches being closed at a second frequency equal to one half the first frequency with a duty cycle of approximately 50%, except as interrupted for the closure of the third switches, and the second switches being closed at the second frequency with a duty cycle of approximately 50%, except as interrupted for the closure of the third switches;
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operating the first and second switches at a first frequency; and
,operating the third switches at a second frequency; the ratio of the frequencies being two to one. - View Dependent Claims (25, 26, 27, 28)
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Specification