Two-Phase Threshold Detector Circuit for Overshoot Control
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Solution Overview
Problem
High-speed switched-capacitor circuits face inaccuracies due to output voltage overshoot caused by finite delay in threshold detectors, which varies with process, temperature, and output signal, leading to nonlinearity and errors in analog-to-digital converters.
Innovation Solution
Implementing a two- or multi-phase threshold detection method where the coarse phase output is sampled and placed in series with the fine current source, reducing the effect of finite output resistance and maintaining a constant ramp rate across a wide range of output voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a single-phase threshold detector is used to achieve high-speed operation, then the circuit speed is improved, but output voltage overshoot increases due to finite detector delay
Solution Approach 1:
The patent divides the threshold detection process into two distinct phases: a coarse detection phase that quickly identifies the general threshold crossing region, and a fine detection phase that precisely determines the final threshold crossing point. This segmentation allows the circuit to achieve both high speed (through rapid coarse detection) and high precision (through careful fine detection), resolving the contradiction between speed and accuracy.
2Productivity
If the ramp rate is increased to maintain operation within the available time, then the circuit can operate faster, but the output overshoot increases due to threshold detector delay
Solution Approach 1:
The patent segments the ramping process into two phases corresponding to coarse and fine detection. During the coarse phase, a higher ramp rate is used to quickly traverse most of the voltage range. During the fine phase, the ramp rate is reduced to minimize overshoot when approaching the threshold. This temporal segmentation of ramp rates allows the circuit to maintain high productivity while controlling harmful overshoot.
Solution Approach 2:
The coarse detection phase performs preliminary action by quickly identifying the region where threshold crossing will occur. This preliminary information allows the fine detection phase to begin with adjusted parameters (lower ramp rate) that are optimized for precision, preventing excessive overshoot before it occurs.
3Measurement precision
If the threshold detector delay is reduced to minimize overshoot, then output accuracy improves, but circuit complexity increases
Solution Approach 1:
Rather than attempting to reduce detector delay through complex circuit modifications, the patent segments the detection process into coarse and fine phases. This approach achieves high precision using two simpler detector stages rather than one complex fast detector, thereby improving accuracy while minimizing the increase in circuit complexity.
Data Source
AI summary
A switched capacitor circuit includes a threshold detector to generate a threshold detection signal when a difference between first and second input signals crosses a predetermined level. A coarse current source produces a coarse ramp. A series sampling capacitor samples a coarse output voltage when the threshold detector indicates a first threshold crossing. The sampling capacitor is connected in series with a fine current source producing a fine ramp.