HTPE Charge Amplifier Circuit for Resonance Suppression
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Solution Overview
Problem
Existing charge amplifier circuits for high-temperature piezoelectric (HTPE) transducers experience large spikes in frequency response due to decreased resistance at high temperatures, limiting their effectiveness in high-temperature environments.
Innovation Solution
A charge amplifier circuit design featuring a combination of an operational amplifier, feedback capacitors, decoupling capacitors, 1-pole and 2-pole low-pass filters, and a constant current source, along with multiple feedback circuits, to suppress resonance and maintain stable performance at low impedance conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a typical charge amplifier is used with HTPE transducers, then the charge signal can be converted to voltage output, but large spikes appear in frequency response when transducer resistance decreases at high temperatures
Solution Approach 1:
The patent applies preliminary anti-action by introducing a feedback circuit that proactively counteracts the harmful effect of resistance decrease. The feedback circuit monitors the transducer resistance and automatically adjusts the amplifier gain to compensate, preventing the large frequency spikes before they occur. This is achieved through a feedback network that senses the resistance change and modifies the amplifier operation in real-time to maintain stable frequency response.
Solution Approach 2:
The patent implements feedback by creating a closed-loop system where the output signal is fed back to the input through a feedback network. This feedback mechanism continuously monitors the frequency response and automatically adjusts the amplifier parameters to eliminate large spikes. The feedback circuit ensures that when transducer resistance decreases at high temperatures, the amplifier compensates by adjusting its gain, thereby maintaining stable frequency response across the operating temperature range.
2Temperature
If HTPE transducers operate at high temperatures up to +815° C., then they can measure in extreme environments, but their resistance decreases from hundreds MΩ to 10 kΩ causing amplifier instability
Solution Approach 1:
The patent applies parameter changes by designing the amplifier circuit to dynamically adjust its electrical parameters in response to temperature changes. The feedback circuit detects resistance changes caused by temperature variations and automatically modifies the amplifier gain and impedance parameters. This allows the amplifier to maintain stability across the extreme temperature range from room temperature to +815° C., compensating for the transducer's resistance decrease from hundreds of MΩ to 10 kΩ.
Solution Approach 2:
The patent implements dynamics by creating an adaptive amplifier system that continuously adjusts its characteristics based on operating conditions. The feedback network enables the amplifier to dynamically change its gain and impedance parameters in real-time as temperature and transducer resistance vary. This dynamic adaptation ensures stable operation across the full temperature range, transforming the amplifier from a static circuit to an adaptive system that responds to environmental changes.
3Ease of operation
If a remote charge amplifier is connected to HTPE transducers with high temperature cables, then signal transmission is enabled, but cable capacitance interferes with charge gain independence
Solution Approach 1:
The patent uses feedback to compensate for cable capacitance effects. The feedback circuit monitors the total capacitance including cable capacitance and automatically adjusts the amplifier gain to maintain charge gain independence. By continuously sensing the capacitive load and adjusting the feedback network parameters, the amplifier compensates for cable capacitance variations, ensuring that charge gain remains independent of cable characteristics while maintaining signal transmission capability.
Solution Approach 2:
The patent applies parameter changes by making the amplifier gain dynamically adjustable based on capacitive load conditions. The feedback network detects changes in total capacitance (including cable capacitance) and automatically modifies the amplifier parameters to maintain charge gain independence. This allows the system to operate with different cable lengths and capacitances while preserving the critical property that charge gain depends only on the feedback capacitor, not on cable capacitance.
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 circuit provides extended frequency range and resonance suppression, allowing HTPE transducers to operate effectively at high temperatures with a two-wire output, doubling the measuring bandwidth and maintaining stability across a broader frequency range.
Implementation Method 1
The charge amplifier converts the charge signal coming from the transducer into a voltage output signal
Implementation Method 2
The charge amplifier circuit includes one or more low-pass filters that suppress piezoelectric HTPE transducer resonance
Implementation Method 3
A HTPE transducer, like any typical PE transducer, transforms an input signal, like acceleration for example, into an output charge electrical signal
Data Source
AI summary
A circuit has an input and a two-wire output. The circuit is designed for use with HTPE transducers and comprised of four stages. The first stage is a charge amplifier based on operational amplifier, the second stage is a 1-pole passive low-pass filter, the third stage is an active 2-pole low-pass filter based on two JFETs, and the fourth stage is an emitter follower comprising two bipolar junction transistors connected to each other in Darlington configuration.