Transistor Polyphase Filter for Compact High-Frequency Operation
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Solution Overview
Problem
Conventional RC polyphase filters face challenges in downsizing and high-frequency operation due to the limitations of minimum size MIM capacitance and impedance matching, making it difficult to achieve efficient high-frequency performance.
Innovation Solution
A polyphase filter design utilizing transistors instead of MIM capacitors, where the connections between transistors allow for reduced size and increased frequency capability by using the gate-source capacitance and drain-source resistance to match impedance, enabling downsizing and high-frequency operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If MIM capacitors are used in conventional RC polyphase filters, then the filter can be constructed with standard components, but the minimum size of MIM capacitance prevents downsizing and high frequency operation
Solution Approach 1:
The patent changes the fundamental parameter of capacitance implementation by replacing physical MIM capacitors with the intrinsic gate-source capacitance of transistors. This parameter change enables the filter to operate at high frequencies with reduced area, as transistor capacitance can be made arbitrarily small by scaling transistor dimensions, unlike MIM capacitors which are constrained by minimum fabrication rules.
2Speed
If capacitance value is decreased for high frequency operation, then the filter can operate at higher frequencies, but the minimum size of MIM capacitance prevents further reduction
Solution Approach 1:
The patent substitutes the mechanical/physical MIM capacitor structure with the electrical property of transistor gate-source capacitance. This substitution allows the capacitance value to be effectively reduced to near-zero by using small-signal operation and biasing conditions, enabling high-frequency operation without being constrained by minimum MIM capacitor size rules.
3Ease of manufacture
If conventional RC polyphase filter structure is used, then the circuit can be implemented with resistors and capacitors, but the impedance matching requirements increase the component size
Solution Approach 1:
The patent makes the transistor serve multiple functions simultaneously: it provides the capacitance value through gate-source capacitance, the resistance value through drain-source resistance, and enables impedance matching through its controlled impedance characteristics. This multi-functionality eliminates the need for separate resistors and capacitors, significantly reducing the overall circuit area while maintaining ease of manufacture using standard transistor fabrication.
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
The transistor-based polyphase filter achieves downsizing and high-frequency operation by leveraging the smaller size of transistors and controlled impedance, overcoming the limitations of conventional MIM capacitor-based filters.
Implementation Method 1
the impedance of the capacitance is 1/ωC
Implementation Method 2
Their resistance value and capacitance value which are required at this time are equal to the impedance of the input terminals and the impedance of the output terminals
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
A first input terminal (11) is connected to a point of connection of a drain terminal of a first transistor (1) and a gate terminal of a fourth transistor (4). A second input terminal (12) is connected to a point of connection of a drain terminal of a third transistor (3) and a gate terminal of a second transistor (2). One of first through fourth output terminals (21) to (24) is connected to a source terminal of each of the first through fourth transistors (1) to (4). A gate terminal of the first transistor (1) and a drain terminal of the second transistor (2) are connected, and a gate terminal of the third transistor (3) and a drain terminal of the fourth transistor (4) are connected.