Compensated Attenuator Circuit for Oscilloscope Attenuation Matching
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Solution Overview
Problem
Existing attenuation circuits in oscilloscopes face challenges in matching low frequency and high frequency attenuation values, leading to errors such as settling tails due to parasitic capacitances and component tolerance errors, which are costly and require manual adjustment or additional power consumption.
Innovation Solution
A cascaded configuration of resistive and capacitive dividers with programmable trim capacitors is used to achieve N:1 signal attenuation, allowing for software-controlled adjustment of high frequency attenuation to match low frequency attenuation, minimizing errors and reducing manufacturing costs and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If manual trim capacitors are used to compensate high frequency attenuation variability, then measurement precision is improved, but manufacturing cost and time increase due to manual adjustment
Solution Approach 1:
The patent replaces manual mechanical adjustment of trim capacitors with an automated electronic control system. A microcontroller automatically adjusts the capacitance values of variable capacitors based on measured attenuation characteristics, eliminating the need for manual intervention while maintaining high precision matching between low and high frequency attenuation paths.
Solution Approach 2:
The attenuation compensation system performs self-calibration by automatically measuring its own attenuation characteristics and adjusting the variable capacitors accordingly. The system uses an internal test signal generator and measurement circuitry to detect attenuation mismatches and autonomously correct them, making the manufacturing process self-sufficient without external manual adjustment.
2Adaptability or versatility
If varactor diodes are used to achieve capacitance swings, then adaptability is improved, but power consumption increases and additional space is required on PCB
Solution Approach 1:
The patent employs digitally controlled variable capacitors that can be adjusted in discrete steps through software control, replacing varactor diodes that require continuous analog control and additional support circuitry. This approach reduces power consumption by eliminating the need for continuous biasing voltages and complex control electronics, while still providing sufficient capacitance adjustment range for compensation.
Solution Approach 2:
The patent extracts the essential function of capacitance adjustment from complex varactor diode circuits with their supporting bias networks and control electronics. By using simpler digitally controlled variable capacitors, the design removes unnecessary power-consuming components while retaining the core adaptability needed for attenuation matching.
3Adaptability or versatility
If varactor diodes with additional support circuitry are used, then adaptability is improved, but device complexity increases
Solution Approach 1:
The patent merges the capacitance adjustment function directly into the existing attenuation circuit by integrating variable capacitors into the high frequency attenuation path. This eliminates the need for separate varactor diode circuits and their associated support electronics, reducing overall device complexity while maintaining the ability to adjust capacitance for attenuation matching.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively minimizes signal errors by matching high and low frequency attenuations, reducing manufacturing costs and power consumption, and enabling precise signal representation in oscilloscopes.
Implementation Method 1
The resistive divider is used to attenuate low frequency signals
Implementation Method 2
the capacitive divider is used to attenuate high frequency signals
Implementation Method 3
such a circuit can be viewed as ideal if the RC time constant of the upper leg of the circuit matches the RC time constant of the lower leg of the circuit
Data Source
AI summary
An attenuator circuit. The attenuator circuit includes a resistive divider coupled to a capacitive network including first and second capacitive dividers. The resistive divider is configured to perform an N:1 attenuation of a signal in a low frequency range. The first and second capacitive dividers are configured to perform an N:1 attenuation in the high frequency range that is a product of the attenuation provided by each (e.g., each performing an M:1 attenuation, where N=M×M, with the total attenuation of the capacitive dividers being N:1 where N=M×M). A variable capacitance divider is coupled in parallel with the second capacitive divider, and includes first and second variable capacitors that, when adjusted, change the high frequency attenuation of the attenuator circuit to match the value of the high frequency attenuation to that of the low frequency attenuation.