Switched Reference Buffer for Low-Offset ADC Transient Response
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Solution Overview
Problem
Reference buffers for analog-to-digital converters (ADCs) require a fast transient response time with minimal power consumption and must minimize systematic or random offset to avoid gain errors.
Innovation Solution
A reference buffer design that alternates between closed-loop and open-loop phases, utilizing a flipped voltage-follower configuration and chopper stabilization to maintain accurate output voltage while minimizing power consumption and offset errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the reference buffer operates in continuous closed-loop mode to minimize offset, then offset error is reduced, but transient response time increases and power consumption rises
Solution Approach 1:
The reference buffer dynamically switches between closed-loop and open-loop modes based on operational requirements. During settling phase, it operates in closed-loop mode to minimize offset. During conversion phase with transient spikes, it switches to open-loop mode for fast response. This dynamic mode switching resolves the contradiction between offset minimization and transient response speed.
Solution Approach 2:
The reference buffer employs periodic alternating phases of closed-loop and open-loop operation. The closed-loop phase corrects offset errors periodically, while the open-loop phase handles transient responses. This periodic alternation allows the system to achieve both low offset and fast transient response at different time intervals.
2Measurement precision
If the reference buffer operates in continuous closed-loop mode to minimize offset, then offset error is reduced, but power consumption increases
Solution Approach 1:
The reference buffer performs closed-loop offset correction only during specific settling phases rather than continuously. During conversion phases, it switches to open-loop mode which consumes less power. This periodic execution of power-intensive closed-loop operation reduces overall power consumption while still achieving adequate offset minimization.
Solution Approach 2:
The reference buffer performs offset correction in advance during the settling phase before the actual conversion begins. By completing the offset minimization operation beforehand, the system can then switch to a lower-power open-loop mode during the conversion phase, reducing overall power consumption while maintaining accuracy.
3Speed
If the reference buffer increases bandwidth to handle transient spikes, then transient response improves, but offset error increases
Solution Approach 1:
The reference buffer dynamically adjusts its operating mode based on the operational phase. During conversion phase when transient spikes occur, it operates in open-loop mode with high bandwidth for fast response. During settling phase, it switches to closed-loop mode with lower bandwidth to minimize offset. This dynamic adaptation resolves the contradiction between bandwidth and offset.
Data Source
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AI summary
A reference buffer is disclosed. The reference buffer includes an amplifier configured to amplify a difference between a reference output voltage and a reference input voltage during a closed-loop phase of the reference buffer. The reference buffer also includes a sample circuit configured to sample an amplifier output voltage during the closed-loop phase. The reference buffer further includes a buffer circuit having a buffer input coupled to the sample circuit and a buffer output configured to provide the reference output voltage. The reference buffer also includes first and second switch circuits. The first switch circuit is configured to isolate the sample circuit from the output stage of the amplifier during an open-loop phase of the reference buffer. The second switch circuit is configured to isolate the input stage from the output of the reference buffer during the open-loop phase.