Multimeter Amplifier Circuit with Negative Integrating Driver
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Solution Overview
Problem
Conventional multimeter amplifier circuits face challenges in achieving high signal-to-noise ratio, stable high input impedance, and good high-frequency performance due to low gain and stray capacitance issues.
Innovation Solution
The proposed amplifier circuit employs a negative integrating driver circuit with operational amplifiers configured as voltage-followers, utilizing resistors and capacitors to set integration time constants, ensuring high input impedance and adequate frequency response, and includes a configuration where the output is connected to an input terminal to maintain voltage inversion and prevent current flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a high resistance input resistor (1 MΩ) is used to achieve high input impedance, then input impedance is improved, but the gain of the amplifier becomes very low (0.01)
Solution Approach 1:
The amplifier circuit is divided into multiple stages: a first operational amplifier with voltage follower configuration provides high input impedance, while a second operational amplifier with inverting amplifier configuration provides the necessary gain. This segmentation allows each stage to optimize for its specific function without compromising the other.
Solution Approach 2:
The patent transitions from a single-stage amplifier to a two-stage amplifier architecture, adding a temporal and functional dimension to the signal processing. The first stage handles impedance matching while the second stage handles amplification, effectively solving the contradiction by operating in different functional dimensions.
2Power
If a high gain amplifier is used to boost the attenuated signal, then signal magnitude is improved, but the signal-to-noise ratio becomes very low due to noise amplification
Solution Approach 1:
The first operational amplifier stage performs preliminary signal conditioning by providing high input impedance and unity gain buffering before the signal is passed to the second amplification stage. This preliminary action prevents noise introduction at the input stage while maintaining signal integrity.
Solution Approach 2:
The first operational amplifier stage acts as an intermediary between the high impedance input source and the high gain second stage. It buffers the signal, preventing direct coupling of high impedance effects into the high gain stage, thereby maintaining signal-to-noise ratio while enabling necessary amplification.
3Stability of the object's composition
If an input resistor (1 MΩ) is used to fix input impedance at a constant value, then input impedance stability is improved, but stray capacitance and input capacitance form a low-pass filter that limits AC response
Solution Approach 1:
The patent extracts the impedance-stabilizing function from the signal path by using the first operational amplifier in voltage follower configuration. The input resistor is removed from the signal path, and input impedance is stabilized through the operational amplifier's high impedance characteristics, eliminating the low-pass filter effect while maintaining impedance stability.
Solution Approach 2:
The patent replaces the passive RC low-pass filter mechanism with an active operational amplifier-based impedance stabilization mechanism. This substitution eliminates the frequency-limiting capacitor-resistor interaction while maintaining the desired input impedance characteristics across a broader frequency range.
Data Source
AI summary
An amplifier circuit is used in a multimeter to amplify signals applied between a pair of test terminals. A voltage applied to one of the test terminals is amplified by a first operational amplifier configured as a voltage follower. An output of the first operational amplifier is applied to an inverting input of a second operational amplifier configured as an integrator. An output of the second operational amplifier is connected to the other of the test terminals. A voltage generated at the output of the second operational amplifier provides an indication of the magnitude and polarity of the voltage applied to the first and second test terminals.