Multi-Finger Transistor Bias Isolation for Uniform Amplification
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Solution Overview
Problem
In multi-finger transistors, uneven operation of unit transistors occurs due to differences in input impedance caused by temperature variations or individual differences, leading to undesirable amplification characteristics.
Innovation Solution
A multi-finger transistor configuration with a common input terminal, common bias terminal, and common output terminal, along with first resistance elements that cut direct current components of the bias current, ensures even operation of unit transistors by equalizing the bias current distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the bases of a plurality of unit transistors are electrically connected in parallel without necessarily via a DC cut capacitor, then the device complexity is reduced, but the operation uniformity of unit transistors deteriorates due to uneven bias current distribution
Solution Approach 1:
The patent divides the multi-finger transistor into separate unit transistors (fingers) with individual DC cut capacitors for each base. This segmentation allows independent bias current control for each unit transistor, preventing the uneven current distribution that would occur with direct parallel connection, while still maintaining the overall multi-finger structure for high current handling capability.
Solution Approach 2:
The patent introduces DC cut capacitors as intermediary elements between the common input terminal and each unit transistor base. These capacitors act as mediators that block DC components while allowing AC signals to pass, thereby preventing DC bias current from flowing unevenly into individual transistor bases while maintaining signal integrity.
2Manufacturing precision
If individual differences between unit transistors are present, then manufacturing precision is reduced, but the bias current distribution becomes uneven causing deterioration in amplification characteristics
Solution Approach 1:
By providing separate DC cut capacitors for each unit transistor base, the patent enables independent compensation for individual transistor variations. Each capacitor can be optimized to account for manufacturing tolerances and individual differences in that specific transistor, ensuring uniform bias current distribution despite variations in transistor characteristics.
Solution Approach 2:
The patent allows for adjustment of capacitor values to compensate for individual transistor differences. By changing the capacitance parameters of individual DC cut capacitors, the bias current distribution can be optimized to account for manufacturing variations, ensuring that each unit transistor operates uniformly regardless of individual differences.
Data Source
AI summary
A multi-finger transistor includes unit transistors each including a first terminal electrically connected to a reference potential, a second terminal that receives an RF signal and a bias current, and a third terminal that outputs an amplified signal; a common input terminal electrically connected in parallel to the second terminals of the unit transistors and that receives the RF signal; a common bias terminal electrically connected in parallel to the second terminals of the unit transistors and that receives the bias current; a common output terminal electrically connected in parallel to the third terminals of the unit transistors and that outputs the amplified signal; and first resistance elements each of which is electrically connected between the common input terminal and the second terminal of a corresponding one of the unit transistors and each of which cuts a DC component of the bias current.