Switched capacitor amplifier with higher gain and improved closed-loop gain accuracy
First Claim
1. An amplifier circuit, comprising:
- a first stage amplifier having an input terminal and an output terminal, the first stage amplifier being configured to operate with positive feedback;
a second stage amplifier having an input terminal and an output terminal, the input terminal of the second stage amplifier being coupled to the output terminal of the first stage amplifier, the first stage amplifier and the second stage amplifier together forming an inverting amplifier between the output terminal of the second stage amplifier and the input terminal of the first stage amplifier;
a first feedback capacitor connected between the output terminal of the second stage amplifier and the input terminal of the first stage amplifier, the first feedback capacitor being operable to provide negative feedback from the output terminal of the second stage amplifier to the input terminal of the first stage amplifier; and
a second feedback capacitor connected between the output terminal of the first stage amplifier and a non-inverting input terminal of the first stage amplifier, the second feedback capacitor being operable to provide positive feedback to the first stage amplifier.
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Accused Products
Abstract
A switched capacitor CMOS amplifier uses a first stage non-inverting CMOS amplifier driving a second stage inverting CMOS amplifier. The first stage amplifier is provided with positive feedback to substantially increase the gain of the first stage amplifier. In the described examples, the positive feedback is provided either by connecting a capacitor from the output to the input of the first stage amplifier or by connecting a shunt transistor in parallel with an input transistor and driving the transistor from the output of the first stage amplifier. The substantially increased gain resulting from the positive feedback allows the gain of the switched capacitor amplifier to be set by the ratio of the capacitance of an input capacitor to the capacitance of a feedback capacitor. The amplifier also includes switching transistors for periodically discharging the input capacitor and the feedback capacitor.
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Citations
26 Claims
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1. An amplifier circuit, comprising:
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a first stage amplifier having an input terminal and an output terminal, the first stage amplifier being configured to operate with positive feedback; a second stage amplifier having an input terminal and an output terminal, the input terminal of the second stage amplifier being coupled to the output terminal of the first stage amplifier, the first stage amplifier and the second stage amplifier together forming an inverting amplifier between the output terminal of the second stage amplifier and the input terminal of the first stage amplifier; a first feedback capacitor connected between the output terminal of the second stage amplifier and the input terminal of the first stage amplifier, the first feedback capacitor being operable to provide negative feedback from the output terminal of the second stage amplifier to the input terminal of the first stage amplifier; and a second feedback capacitor connected between the output terminal of the first stage amplifier and a non-inverting input terminal of the first stage amplifier, the second feedback capacitor being operable to provide positive feedback to the first stage amplifier. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. An amplifier circuit, comprising:
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a first stage amplifier having an input terminal and an output terminal, the first stage amplifier being configured to operate with positive feedback; an input capacitor connected between an amplifier input terminal and the input terminal of the first stage amplifier; a second stage amplifier having an input terminal and an output terminal, the input terminal of the second stage amplifier being coupled to the output terminal of the first stage amplifier, the first stage amplifier and the second stage amplifier together forming an inverting amplifier between the output terminal of the second stage amplifier and the input terminal of the first stage amplifier; and a first feedback capacitor connected between the output terminal of the second stage amplifier and the input terminal of the first stage amplifier, the first feedback capacitor being operable to provide negative feedback from the output terminal of the second stage amplifier to the input terminal of the first stage amplifier. - View Dependent Claims (15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26)
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Specification