Polyphase Filter Circuit Using FET Elements for Phase Stability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing polyphase filter circuitry suffers from significant distortion, particularly at high frequencies, and exhibits large amplitude and phase variations across process corners due to sensitivity to resistor and capacitor variations, leading to inadequate design margin and performance issues.
Innovation Solution
The polyphase filter circuitry is redesigned to use field-effect transistors for both resistors and capacitors, with specific configurations of source-follower and common-source amplifier circuits to define frequency response, reducing the number of components and minimizing the impact of process deviations, thereby stabilizing phase and amplitude across different process corners.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional polyphase filter circuitry is used, then the circuit can generate multiple output signals with different relative phases, but the circuit suffers from significant distortion particularly at high frequencies and large amplitude and phase variations across process corners
Solution Approach 1:
The patent changes the fundamental parameters of the filter circuit by replacing traditional resistor-capacitor implementations with field-effect transistor-based implementations. Specifically, resistors are replaced with transistors operating in specific regions, and capacitors are replaced with transistor gate capacitances, fundamentally altering the circuit's electrical characteristics and reducing sensitivity to process variations
Solution Approach 2:
The patent substitutes passive mechanical/electrical components (resistors and capacitors) with active semiconductor devices (field-effect transistors). This substitution allows the circuit to achieve the same filtering function while being less sensitive to process corner variations, as transistor parameters can be better controlled and matched in modern CMOS fabrication processes
2Reliability
If the number of components is reduced to minimize impact of process deviations, then the circuit becomes more stable across process corners, but the circuit complexity and design difficulty increase
Solution Approach 1:
The patent makes field-effect transistors perform multiple functions simultaneously. Each transistor serves as both a filtering element (replacing RC components) and an amplifying/buffering element. The source-follower and common-source configurations provide both signal processing and impedance transformation functions, reducing the total component count while maintaining stability
Solution Approach 2:
The patent merges the functions of multiple discrete components into integrated transistor circuits. The source-follower and common-source amplifier stages are combined to create a unified polyphase filter structure where impedance transformation, signal buffering, and frequency filtering are achieved through the coordinated action of coupled transistors rather than separate discrete components
Data Source
AI summary
Polyphase filter circuitry including: an input node to receive an input signal VIN having a dominant frequency fPPF; and a common-source amplifier circuit. The common-source amplifier circuit includes a field-effect transistor M1 with its gate terminal connected to the input node and with a capacitor CPFF connected to its source terminal; and for the common-source amplifier circuit, the output resistance RM1 at the source terminal of the field-effect transistor M1 and the capacitance of the capacitor CPFF are define the frequency response of the common-source amplifier circuit so that, based on the input signal VIN, a signal VLEAD is generated at the drain terminal of the transistor M1 which leads the input signal VIN in phase by a given phase shift ΔϕLEAD and a signal VLAG is generated at the source terminal of the transistor M1 which lags the input signal VIN in phase by a given phase shift ΔϕLAG.