Voltage-Controlled Attenuator With FET Resistance Feedback
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Solution Overview
Problem
Current voltage-controlled variable gain amplifiers and attenuators suffer from precision issues due to process variation and temperature sensitivity, leading to image artifacts in medical and industrial imaging systems, and they rely on complex and costly piece-wise linear approximation techniques.
Innovation Solution
A high-precision voltage-controlled variable gain circuit element that 'slaves' a FET resistor to a reference resistor, using current source circuits and operational amplifiers to maintain resistance equality, thereby achieving temperature and process-independent gain control through a mathematical formula.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If piece-wise linear approximation techniques are used to control gain in voltage-controlled variable gain amplifiers, then gain control can be achieved, but manufacturing precision deteriorates to ±1 dB due to process variation and temperature sensitivity
Solution Approach 1:
The patent employs feedback mechanisms where the actual gain is continuously monitored and compared against the desired gain, and the control voltage is adjusted accordingly to compensate for process variations and temperature drift, achieving stable ±0.2 dB precision without requiring complex piece-wise linear approximation circuits
Solution Approach 2:
The patent changes the control parameter from voltage to current, utilizing the more stable and temperature-insensitive characteristics of current sources. By controlling gain through current ratios rather than voltage levels, the system achieves better immunity to process variations and temperature effects, improving both manufacturing precision and reliability
2Ease of operation
If complex piece-wise linear approximation circuits are used to achieve gain control, then gain adjustment is possible, but device complexity increases and cost increases
Solution Approach 1:
The patent extracts and eliminates the complex piece-wise linear approximation circuits from the design, replacing them with a simplified current-based control mechanism. By removing the unnecessary complex circuitry while retaining the essential gain control function through current sources and transconductance amplifiers, the device complexity is reduced without sacrificing operational capability
Solution Approach 2:
The patent substitutes the mechanical-like complex circuit architecture with a more elegant electronic current-based control system. Instead of using complex voltage-based approximation circuits, the invention uses current sources and transconductance amplifiers to achieve smooth gain control, simplifying the overall device structure and reducing component count
3Adaptability or versatility
If voltage-controlled FET resistors are used for attenuation control, then variable gain can be achieved, but manufacturing precision deteriorates due to poor resistance precision of FET resistors
Solution Approach 1:
The patent introduces current sources as intermediary elements between the control voltage and the FET resistors. By using current sources to control the FET resistors rather than applying control voltages directly, the system achieves better precision because current sources are less sensitive to process variations and temperature effects, thereby improving the effective resistance precision while maintaining variable gain capability
Data Source
AI summary
A circuit includes a first variable resistor having a resistance which is variable in response to a resistance control signal. A resistance control circuit includes a first current source circuit for supplying a first current through a reference resistor. A second current source circuit supplies a second current through the first variable resistor. In operational amplifier has a first input coupled to a first conductor connecting the first current source to the reference resistor, a second input coupled to a second conductor connecting the current source to the first variable resistor, and an output applying the first resistance control signal to a control terminal of the first variable resistor, to force the resistance of the first variable resistor to be equal to a resistance of the reference resistor. The resistance of a second variable resistor of an attenuator is controlled in response to the resistance control signal.