Signal Acquisition Probe With Reduced Capacitive Loading
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Traditional passive voltage probes load the device under test due to high probe tip capacitance, which affects bandwidth and signal-to-noise ratio, and existing solutions either increase resistance, reducing signal input or require adjustments that compromise frequency response.
Innovation Solution
A signal acquisition system with a signal acquisition probe and processing instrument featuring mismatched time constants, utilizing a shunt pole-zero pair and feedback loop circuitry to maintain flat frequency response, and reducing probe tip capacitance to 2-5 picofarads, with compensatory pole-zero pairs in the input circuitry to enhance bandwidth and signal integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional passive voltage probes are used, then the probe provides voltage measurement capability, but the high probe tip capacitance loads the device under test and degrades signal quality
Solution Approach 1:
The patent changes the capacitance parameter of the probe tip from traditional values (typically 10-20 pF) to a reduced value (2-5 pF), fundamentally altering the electrical characteristics of the probe to minimize loading effects on the device under test while maintaining measurement accuracy through compensated frequency response
2Object-affected harmful factors
If probe tip capacitance is reduced to increase input impedance, then capacitive loading is reduced, but the frequency response becomes non-flat requiring complex compensation
Solution Approach 1:
The patent employs feedback circuitry within the probe that senses the signal and applies corrective action to maintain a flat frequency response despite the reduced capacitance, automatically compensating for the changed electrical characteristics without requiring manual adjustment
Solution Approach 2:
The patent modifies the electrical parameters of the compensation circuitry to match the reduced capacitance value, changing the resistance and capacitance values in the compensation network to achieve proper time constant matching and flat frequency response across the measurement bandwidth
3Object-affected harmful factors
If resistance is increased to maintain time constant with reduced capacitance, then capacitive loading is reduced, but signal attenuation increases
Solution Approach 1:
The patent optimizes the resistance parameter in the voltage divider network to achieve the correct attenuation ratio while accounting for the reduced capacitance, balancing the time constant relationship without excessive signal loss by precisely matching the resistance values to the new capacitance configuration
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 system achieves reduced capacitive loading of the device under test, increased high-frequency input impedance, and improved signal-to-noise ratio by effectively managing mid-band and high-band frequency signal current, while maintaining compatibility with legacy probes.
Implementation Method 1
utilizing a shunt pole-zero pair and feedback loop circuitry to maintain flat frequency response, and reducing probe tip capacitance to 2-5 picofarads, with compensatory pole-zero pairs in the input circuitry
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
A signal acquisition system (50) has a signal acquisition probe (52) having probe tip circuitry coupled to a resistive center conductor signal cable (54). The resistive center conductor signal cable of the signal acquisition probe is coupled to a compensation system (68) in a signal processing instrument via an input node and input circuitry in the signal processing instrument. The signal acquisition probe and the signal processing instrument have mismatched time constants at the input node with the compensation system having an input amplifier with feedback loop circuitry and a shunt pole-zero pair coupled to the input circuitry providing pole-zero pairs for maintaining flatness over the signal acquisition system frequency bandwidth.