Double-Switched Track-and-Hold Circuit for Feed-Through Isolation
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Solution Overview
Problem
Prior art track-and-hold circuits with very wide bandwidth suffer from sample amplitude accuracy degradation due to non-linearity and hold-mode signal feed-through, resulting from design tradeoffs between bandwidth, linearity, and hold-mode droop, where increased linearity is typically achieved at the expense of bandwidth and feed-through.
Innovation Solution
A double switched track-and-hold circuit with an input buffer having a first switched amplifier circuit and a track-and-hold core circuit with a second switched amplifier circuit, both turning off simultaneously during the hold mode to provide enhanced isolation, along with a clamping diode circuit to further reduce signal feed-through, achieving high bandwidth and low nonlinearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If large transistors are used in the emitter-follower to achieve high linearity, then linearity is improved, but bandwidth is reduced and hold-mode feed-through increases
Solution Approach 1:
The patent divides the switching function into two separate stages: a first switched amplifier circuit in the input buffer and a second switched amplifier circuit in the track-and-hold core. Each stage uses smaller transistors optimized for its specific function, avoiding the need for large transistors in a single stage while maintaining overall linearity and bandwidth performance.
Solution Approach 2:
The input buffer acts as an intermediary stage between the input signal and the track-and-hold core. It includes a first switched amplifier circuit that provides additional isolation and signal conditioning, effectively mediating the signal transfer and reducing hold-mode feed-through without requiring large transistors in the core circuit.
2Measurement precision
If large transistors are used in the emitter-follower to achieve high linearity, then linearity is improved, but hold-mode signal feed-through increases
Solution Approach 1:
The switching function is segmented into two independent stages, each with its own smaller transistors. This segmentation reduces the off-state coupling capacitance in each stage compared to a single stage with large transistors, thereby reducing hold-mode signal feed-through while maintaining linearity.
Solution Approach 2:
The input buffer with the first switched amplifier circuit serves as an intermediary that provides an additional isolation stage. This intermediate stage further reduces the signal feed-through path from the input to the hold capacitor, effectively suppressing hold-mode signal feed-through.
3Speed
If bandwidth is increased to achieve fast sampling, then sampling speed is improved, but sample amplitude accuracy degrades due to non-linearity and feed-through
Solution Approach 1:
By segmenting the switching function into two stages with smaller transistors each, the circuit achieves high bandwidth for fast sampling while maintaining low non-linearity and feed-through. Each stage operates with optimized transistor sizes that balance speed and accuracy, avoiding the trade-off present in single-stage designs.
Solution Approach 2:
The input buffer as an intermediary stage provides additional isolation and signal conditioning that preserves amplitude accuracy during high-speed sampling. It reduces the impact of non-linearity and feed-through effects that would otherwise degrade sample accuracy at high sampling rates.
Data Source
AI summary
A double switched track-and-hold circuit includes an input buffer having a first switched amplifier circuit for passing an input signal in a track mode and isolating the input signal from a buffer output in a hold mode, and a track-and-hold core circuit responsive to the input buffer and having a second switched amplifier circuit for tracking the input signal in a track mode and isolating the input signal from a track-and-hold output in a hold mode. The first and second switching amplifier circuits turn off approximately simultaneously during the hold mode to provide enhanced isolation.