Differential Pre-Amplifier Threshold Control for Oscilloscope Accuracy
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Solution Overview
Problem
Existing digital storage oscilloscopes face challenges in precisely controlling trigger and threshold voltage levels, particularly due to voltage errors and temperature drift, which affect the accuracy of signal comparison in differential-to-single-ended conversion.
Innovation Solution
The implementation of circuitry comprising a pre-amplifier with differential output, a multiplexer of transistors, a comparator, and a compensation circuit that tracks common mode voltage changes to adjust the threshold voltage, ensuring precise control over trigger comparators and minimizing signal loading.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If differential-to-single-ended conversion is used to drive trigger comparators, then signal processing capability is improved, but voltage errors and temperature drift increase, reducing measurement precision
Solution Approach 1:
The patent implements feedback by using the common mode voltage from the differential pre-amplifier output to dynamically adjust the threshold voltage in the comparator. The compensation circuit continuously monitors and corrects voltage errors and temperature drift effects, creating a closed-loop system that maintains measurement precision while preserving signal processing capability.
Solution Approach 2:
The patent applies parameter changes by dynamically adjusting the threshold voltage parameter based on the common mode voltage level. As the common mode voltage varies during signal processing, the threshold voltage is automatically modified to compensate for voltage errors and temperature drift, ensuring accurate trigger comparisons throughout the operating range.
2Device complexity
If conventional trigger comparator driving is used, then circuit simplicity is maintained, but signal loading effects increase, reducing measurement precision
Solution Approach 1:
The patent introduces an intermediary compensation circuit between the differential pre-amplifier and the comparator. This intermediary component processes the common mode voltage information and generates appropriate threshold adjustments, acting as a mediator that reduces signal loading effects without significantly increasing overall circuit complexity.
3Device complexity
If fixed threshold voltage is used in comparators, then device complexity is reduced, but temperature drift effects increase, worsening reliability
Solution Approach 1:
The patent transitions from a fixed threshold voltage to a dynamic threshold voltage that automatically adjusts in response to temperature and voltage variations. The compensation circuit continuously modifies the threshold voltage parameter to match changing operating conditions, ensuring reliable trigger comparisons while adding only minimal complexity through the use of available common mode voltage information.
Data Source
AI summary
Circuitry includes a pre-amplifier having a differential output, where the differential output corresponds to a common mode voltage; a multiplexer including sets of transistors, each of which has a control input; a comparator including input terminals, a first terminal of the input terminals to receive a signal that is based on an output of the multiplexer, and a second terminal of the input terminals to receive a threshold voltage; a compensation circuit to produce a divided voltage that varies in accordance with variations in the common mode voltage; and an amplifier to receive a predefined voltage and to use the divided voltage to affect the predefined voltage to produce the threshold voltage for the comparator. Signals in the differential output of the pre-amplifier are applicable to corresponding control inputs in the sets of transistors.