N-Path Filter Circuit With Dummy Paths for Spurious Suppression
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Solution Overview
Problem
N-path filters face limitations in operating in a wide band due to the use of baluns, which are difficult to implement, and suffer from spurious components caused by clock signal leakage via parasitic capacitance.
Innovation Solution
A filter circuit design that includes multiple transistors and capacitors for various phases, along with a dummy circuit using inverted signals to cancel out clock signal leakage, eliminating the need for differential signal lines and baluns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a balun is used in the N-path filter to cancel clock signal leakage, then spurious components are suppressed, but the used frequency band is limited and wideband operation cannot be achieved
Solution Approach 1:
The filter circuit is divided into multiple independent paths (first path, second path, third path, fourth path) corresponding to different phases. Each path contains its own transistor and capacitor connected to the signal line, allowing independent optimization of each path's frequency response while collectively achieving wideband operation without requiring a balun
Solution Approach 2:
Instead of using a balun to cancel clock signal leakage, the patent applies inverted clock signals (180-degree phase shifted) to complementary transistors. When one transistor conducts, the other is off, and vice versa, causing their leakage currents to cancel each other out directly at the source, thereby suppressing spurious components while enabling wideband operation
2Object-affected harmful factors
If differential signal lines with a balun are used to cancel clock signal leakage, then spurious components are reduced, but the device complexity increases
Solution Approach 1:
The filter circuit combines the filtering function and clock signal leakage cancellation function into a single integrated structure. The multiple paths with complementary transistors simultaneously perform signal filtering and cancel clock leakage, eliminating the need for separate balun components and differential signal lines, thereby reducing device complexity
Solution Approach 2:
The filter circuit itself generates the cancellation mechanism through its own structure. The complementary transistors in each path automatically produce opposing leakage currents that cancel each other, making the circuit self-correcting without requiring external balun components or complex differential signaling infrastructure
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 design effectively suppresses spurious components and enables wideband operation by canceling out clock signal leakage, without requiring baluns, thus enhancing signal quality.
Implementation Method 1
signal line having a blocking capacitance for blocking a DC component
Implementation Method 2
clock signal of a high frequency may leak out to the RF signal line via a parasitic capacitance formed between the transistors and the RF signal line
Data Source
AI summary
A filter circuit includes: a filter unit which is connected to a signal line and which has transistors and capacitors which constitute paths for N phases, and in which the transistors to which clock signals of N phases are applied electrically connect the capacitors to the signal line; and a dummy unit which has transistors and impedance parts which constitute dummy paths corresponding, respectively, to the paths for the N phases, and in which the transistors to which inverted signals of N phases are applied electrically connect the impedance parts to the signal line.