Transistor Polyphase Filter Layout for High-Frequency Downsizing
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Solution Overview
Problem
Conventional RC polyphase filters face challenges in downsizing and high-frequency operation due to the limitations of polysilicon resistors and metal-insulator-metal (MIM) capacitors, particularly the minimum size of MIM capacitance and increasing impedance with frequency.
Innovation Solution
A polyphase filter design utilizing four transistors, where specific terminals of each transistor are connected to form connection points for input and output terminals, allowing for equivalent RC behavior and enabling downsizing and high-frequency operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional RC polyphase filter uses MIM capacitors, 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 parameters of the filter components by replacing MIM capacitors with transistors operating in specific regions. This substitution allows the filter to achieve the required impedance characteristics through transistor parameters (transconductance, output resistance) rather than fixed capacitor values, enabling downsizing and high-frequency operation.
Solution Approach 2:
The patent substitutes the passive RC structure with an active transistor-based structure. By using transistors to emulate resistive and capacitive behaviors through their small-signal parameters, the design eliminates the need for physical MIM capacitors, thereby achieving downsizing and improved high-frequency performance.
2Manufacturing precision
If conventional RC polyphase filter uses polysilicon resistors and MIM capacitors, then the impedance values can be set according to design requirements, but the component size increases at lower frequencies
Solution Approach 1:
The patent changes the impedance realization method from fixed passive components to controllable active devices. Transistor parameters (bias currents, device dimensions) are adjusted to achieve the required impedance values, allowing the same filter to operate across different frequency ranges without changing physical component sizes.
Solution Approach 2:
The transistor-based structure serves multiple functions simultaneously: it provides both the resistive and capacitive impedance characteristics needed for polyphase filtering, while also enabling gain and frequency tuning. This multi-functionality eliminates the need for separate large-area passive components.
3Speed
If the capacitance value is decreased for high frequency operation, then the impedance of capacitance increases, but the minimum size of MIM capacitance prevents further reduction
Solution Approach 1:
The patent substitutes physical capacitors with transistor-based impedance elements. The capacitive behavior is achieved through the frequency-dependent small-signal parameters of the transistors rather than through physical capacitor structures, eliminating the minimum capacitance constraint imposed by MIM fabrication processes.
Data Source
AI summary
A first input terminal is connected to a point of connection of a drain terminal of a first transistor and a gate terminal of a fourth transistor. A second input terminal is connected to a point of connection of a drain terminal of a third transistor and a gate terminal of a second transistor. One of first through fourth output terminals to is connected to a source terminal of each of the first through fourth transistors to. A gate terminal of the first transistor and a drain terminal of the second transistor are connected, and a gate terminal of the third transistor and a drain terminal of the fourth transistor are connected.