Reference Tracking in Switched-Capacitor Amplifiers for Stable Common Mode
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Solution Overview
Problem
Switched capacitor differential amplifiers experience changes in common mode voltage at the input terminals of operational amplifiers, leading to signal distortions and degradation of the common mode rejection ratio due to variations in input signals during sample phases.
Innovation Solution
A reference generation circuit generates a reference potential that tracks the magnitude of the input signal during the hold phase, ensuring the common mode voltage remains constant by correlating with the input signal changes, thereby minimizing voltage fluctuations at the operational amplifier's input terminals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a switched capacitor differential amplifier uses a fixed reference potential during the hold phase, then the circuit operation is simple, but the common mode voltage at the operational amplifier input terminals changes due to input signal variations, causing signal distortions and degradation of common mode rejection ratio
Solution Approach 1:
The reference potential is changed from a fixed value to a dynamic value that tracks the input signal magnitude. The reference generation circuit produces a time-varying reference potential during the hold phase that corresponds to the instantaneous magnitude of the input signal, thereby maintaining constant common mode voltage at the operational amplifier inputs while handling varying input signals.
Solution Approach 2:
The reference generation circuit implements a feedback mechanism where the input signal magnitude is sensed and used to adjust the reference potential level. This feedback loop ensures that the reference potential automatically adapts to input signal variations, maintaining stable common mode voltage without requiring external manual adjustment.
2Stability of the object's composition
If the reference potential tracks the input signal magnitude dynamically, then the common mode voltage remains stable and signal distortions are reduced, but the circuit complexity increases due to additional tracking circuitry
Solution Approach 1:
The reference generation circuit is designed to perform multiple functions: it generates the reference potential for the hold phase, tracks the input signal magnitude, and maintains common mode voltage stability. By consolidating these functions into a single circuit block, the patent reduces overall system complexity while achieving the desired stability.
Solution Approach 2:
The reference generation circuit is self-regulating and automatically adjusts the reference potential based on the input signal magnitude without requiring external control. The circuit serves itself by using its own output (reference potential) to maintain the stability of the common mode voltage, eliminating the need for additional external stabilization components.
Data Source
AI summary
A reference generation circuit provided according to an aspect of the present invention generates a reference potential at different levels in the hold phase of different cycles in an input path of a switched capacitor differential amplifier. In an embodiment, for each hold phase, the reference generator provides the reference potential with a magnitude that tracks the magnitude of the input signal applied in a corresponding (preceding) sample phase. In case of a single-ended output, the reference potential generated for each hold phase equals the magnitude of one of the inputs on the differential input path. As a result, the common mode voltage at the input terminals of an operational amplifier contained in the switched capacitor differential amplifier is maintained at a desired level.