Voltage-Current Conversion Circuit Thermal Noise Reduction
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Solution Overview
Problem
The signal-to-noise ratio (SN ratio) in voltage-current conversion circuits is limited by thermal noise current generated by resistors, necessitating an improvement in circuit configuration to enhance SN ratio.
Innovation Solution
The proposed voltage-current conversion circuit incorporates an amplifier with specific input configurations and a series connection of resistors between a transistor and an ac ground, where connecting points are connected to the amplifier inputs, reducing thermal noise current and improving SN ratio by applying input voltage signals in a manner that doubles the output voltage while minimizing noise current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a resistor is used for voltage-current conversion, then the conversion function is achieved, but thermal noise current is generated which limits the signal-to-noise ratio
Solution Approach 1:
The patent divides a single resistor into multiple resistors connected in series. By segmenting the resistance element, the thermal noise current is reduced because the noise from multiple smaller resistors in series is less than the noise from one large resistor, while maintaining the same total resistance value for voltage-current conversion.
Solution Approach 2:
The patent introduces an operational amplifier as an intermediary element to achieve voltage-current conversion without relying solely on a resistor. The operational amplifier, combined with the segmented resistors, converts the input voltage to output current while the feedback mechanism minimizes the impact of thermal noise, thereby improving the signal-to-noise ratio.
2Measurement precision
If the resistance value is increased to reduce current, then the voltage-current conversion ratio is improved, but thermal noise current increases which degrades the signal-to-noise ratio
Solution Approach 1:
The patent segments the total resistance into multiple smaller resistor units connected in series. This segmentation allows achieving the required total resistance value for accurate voltage-current conversion while reducing the thermal noise current, as the noise contribution from multiple smaller resistors is lower than from a single large resistor of equivalent total resistance.
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
This configuration effectively reduces noise current, thereby improving the SN ratio by half compared to related art, allowing for more accurate signal conversion and processing.
Implementation Method 1
a predetermined connecting point, among a first connecting point between the first terminal of the transistor and the serial connection, a second connecting point between the ac ground and the serial connection, and one or more third connecting points between the resistors, is connected to the second input of the amplifier, and one of the connecting points other than the predetermined connecting point is connected to the third input of the amplifier
Implementation Method 2
a transistor including a first terminal, a second terminal, and a control terminal electrically connected to an output of the amplifier
Implementation Method 3
a signal-to-noise ratio (SN ratio) is limited by a thermal noise current which is generated by a resistor performing a voltage-current conversion
Implementation Method 4
a serial connection comprising resistors connected in series between the first terminal of the transistor and an ac ground
Data Source
AI summary
According to one embodiment, a voltage-current conversion circuit includes an amplifier first, second and third inputs, a transistor including a first and second terminals, and a control terminal electrically connected to an output of the amplifier, and a serial connection including resistors connected in series between the first terminal and an ac ground, wherein a predetermined connecting point, among a first connecting point between the first terminal and the serial connection, a second connecting point between the ac ground and the serial connection, and one or more third connecting points between the resistors, is connected to the second input, and one of the connecting points other than the predetermined connecting point is connected to the third input.