Voltage Controlled Adjustable Current Source Using Depletion Mode FETs
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Solution Overview
Problem
Current current-regulating diodes (CR diodes) face challenges in achieving high precision and adaptability, particularly in integrated circuits, due to manufacturing inconsistencies and high output conductance, which affect their ability to regulate current effectively across a range of voltages.
Innovation Solution
A voltage-controlled adjustable current source is implemented using a first and second depletion mode FET in series with a fixed resistor, where the second FET operates as a voltage-controlled resistor, and the current-setting control voltage adjusts the regulated current, utilizing gallium-nitride high electron mobility transistors for precise current regulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a variable resistor is added to adjust the current in a CR diode, then the adaptability of the current source is improved, but the device complexity increases and manufacturing precision deteriorates
Solution Approach 1:
The patent changes the operating parameters of the depletion mode FET by applying different gate-source voltages to achieve current adjustment. Instead of adding a variable resistor, the invention uses voltage control at the gate terminal to vary the drain current, thereby adjusting the current output without increasing circuit complexity or compromising manufacturing precision.
Solution Approach 2:
The depletion mode FET serves multiple functions: it acts as both the current regulating element and the voltage-controlled adjustment mechanism. The single device performs what would traditionally require multiple components (FET plus variable resistor), reducing overall device complexity while maintaining adaptability.
2Ease of manufacture
If manufacturing processes are used to create fixed current values, then the ease of manufacture is improved, but the manufacturing precision deteriorates due to process inconsistencies
Solution Approach 1:
The patent employs a feedback mechanism where the gate-source voltage of the depletion mode FET is controlled to maintain precise current regulation. By using voltage control with feedback, the system compensates for manufacturing variations in the FET parameters, achieving high current precision without requiring ultra-precise manufacturing processes.
Solution Approach 2:
Instead of relying on precise manufacturing of fixed resistors, the invention uses electrical parameter control (gate voltage) to set and adjust the current. This approach allows current values to be programmed or adjusted after manufacturing, eliminating the need for high-precision resistor fabrication and compensating for process variations.
3Ease of manufacture
If the output conductance of the CR diode is high, then the ease of manufacture is improved, but the reliability of current regulation deteriorates
Solution Approach 1:
The patent utilizes the voltage-dependent characteristics of the depletion mode FET to control the output conductance. By adjusting the gate-source voltage, the FET operates in different regions, allowing the output conductance to be minimized during regulation. This enables standard fabrication processes to be used while achieving low output conductance and high regulation reliability through operational parameter control.
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 solution enables precise current regulation over a wide range of voltages with reduced output conductance and increased output impedance, overcoming manufacturing deviations and maintaining regulation across a wider voltage range.
Implementation Method 1
The current regulating apparatus includes a first depletion mode field-effect transistor (FET), a second depletion mode FET, and a fixed resistor. The first depletion mode FET operates as an adjustable current source while the second depletion mode FET is controlled to operate as a voltage controlled resistor.
Data Source
AI summary
A current regulating apparatus capable of regulating an electrical current with a high level of precision and over a wide range of voltages includes a first depletion mode field-effect transistor (FET), a second depletion mode FET, and a fixed resistor. The second depletion mode FET and fixed resistor are connected in series and across the gate-source terminals of the first depletion mode FET. The first depletion mode FET operates as an adjustable current source while the second depletion mode FET is controlled to operate as a voltage controlled resistor. The magnitude of current regulated by the current regulating apparatus is determined based on both the resistance of the fixed resistor and a current-setting control voltage applied to the gate of the second depletion mode FET. Various precision values of regulated current can be realized by simply changing the current-setting control voltage.