Two-Stage Switched-Capacitor Amplifier Reset-Phase Stability
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Solution Overview
Problem
Conventional switched-capacitor gain amplifiers face stability issues due to varying feedback factors during different operational phases, making it difficult to design operational amplifiers that maintain stability across both sampling/reset and amplification phases, and existing compensation techniques are costly and sensitive to timing and mismatch.
Innovation Solution
A two-stage switched-capacitor amplifier design with control logic generating phase-specific switching signals to create a shorter feedback path during the sampling phase, reducing capacitive load and design constraints, and using a telescopic and common source amplifier configuration with a voltage level shifter to enhance stability and bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a two-stage OP-AMP is designed for high speed capability and large output voltage swing, then the amplifier performance is improved, but stability issues arise during both reset/sampling phase and amplification phase
Solution Approach 1:
The patent applies dynamics by making the feedback factor variable rather than fixed. During reset/sampling phase, the feedback factor is set to one (beta=1), and during amplification phase, it changes to Cf/(Cf+Cs+Cp). This dynamic adjustment allows the amplifier to maintain stability in both phases while achieving high speed performance, resolving the contradiction between speed and stability.
2Adaptability or versatility
If the feedback factor is set to one during reset/sampling phase, then the amplifier can operate in that phase, but the open loop bandwidth becomes excessively high (e.g., 900MHz vs 100MHz during amplification), making stability design difficult and expensive
Solution Approach 1:
The patent changes the feedback factor parameter dynamically between phases. During reset/sampling, beta=1, and during amplification, beta=Cf/(Cf+Cs+Cp). This parameter change allows the system to adapt to different operational requirements while keeping the design manageable, avoiding the need for excessively high bandwidth design that would increase complexity and cost.
3Stability of the object's composition
If conventional compensation techniques are used to address stability issues, then stability may be improved, but the cost increases due to reference circuitry and the offset voltage is not cancelled
Solution Approach 1:
The patent implements self-service by using the existing capacitors Cs and Cf in the amplifier circuit to perform the stability compensation function. The offset voltage is naturally cancelled during the amplification phase without requiring external reference circuits. This self-service approach achieves stability improvement while avoiding the added cost and complexity of conventional compensation techniques.
Data Source
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AI summary
A switch-capacitor ("SC") amplifier includes a two-stage operational amplifier ("OP-AMP"), an input SC network, and a feedback SC network. The two-stage OP-AMP includes a first OP-AMP stage having an output coupled to an input of a second OP-AMP stage. The input SC network is coupled to an input of the first OP-AMP stage. The feedback SC network is configured to selectively couple the output of the first OP-AMP stage to the input of the first OP-AMP stage during a first phase of operation of the SC amplifier and to couple an output of the second OP-AMP stage to the input of the first OP-AMP stage during a second phase of operation of the SC amplifier.