Track-and-Hold Amplifier Isolation Circuit for Faster Settling
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Solution Overview
Problem
In high frame rate and high resolution imaging applications, track-and-hold amplifiers face challenges with settling time, which affects device performance, and mismatched settling times between amplifiers can introduce noise in the signal, while reducing sampling capacitor size increases kTC noise and increasing supply current increases power consumption.
Innovation Solution
A track-and-hold amplifier with an isolation circuit that isolates transient current during the track phase, allowing for a settling time independent of the amplifier gain, achieved through selective activation of the isolation circuit and redistribution of current to reduce settling time without increasing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the supply current is increased to reduce settling time, then the settling time is improved, but the power consumption increases
Solution Approach 1:
The patent segments the current path by introducing an isolation circuit that separates the transient current during the track phase from the steady-state current. This allows the amplifier to achieve fast settling without requiring continuously high supply current, thus reducing power consumption while maintaining fast settling time performance.
Solution Approach 2:
The isolation circuit is activated preliminarily during the track phase to isolate transient current before it can affect the settling process. This preliminary action prepares the circuit in advance, allowing the amplifier to settle faster without needing increased supply current during the critical settling period.
2Loss of time
If the sampling capacitor size is decreased to reduce settling time, then the settling time is improved, but the kTC noise increases
Solution Approach 1:
The patent segments the capacitor function by using a series combination of capacitors (first capacitor and second capacitor) that together provide the necessary charge storage while presenting a smaller effective capacitance to the settling node. This segmentation allows reduced settling time without proportionally increasing kTC noise.
Solution Approach 2:
The isolation circuit acts as an intermediary element between the sampling capacitor and the amplifier input during the track phase. It mediates the charging process, allowing the capacitor to charge faster without directly coupling all transient current to the amplifier, thereby reducing settling time while controlling noise injection.
3Device complexity
If conventional amplifier design is used, then the circuit is simple, but the settling time is long and dependent on amplifier gain
Solution Approach 1:
The isolation circuit performs preliminary current isolation during the track phase, preparing the amplifier for faster settling by preventing transient current from interfering with the settling process. This preliminary action decouples the settling time from the amplifier gain dependency that plagues conventional designs.
Solution Approach 2:
The isolation circuit serves as an intermediary that mediates between the track phase and hold phase operations. It introduces a controlled current path that allows fast charging during tracking while isolating the amplifier during settling, achieving fast settling times without requiring complex high-speed amplifier design.
Data Source
AI summary
Various embodiments of the present technology may provide methods and apparatus for a track-and-hold amplifier configured to sample and amplify an analog signal. Methods and apparatus for a track-and-hold amplifier according to various aspects of the present invention may provide an isolation circuit configured to isolate transient current in a track-and-hold capacitor during a track phase. According to various embodiments, selective activation of the isolation circuit provides a settling time that is independent of the gain of the amplifier.