High-Order N-Path Filter With Miller Feedback for TX Leakage Rejection
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Solution Overview
Problem
In wireless receivers, transmit (TX) leakage and jammers impose performance limitations on receive (RX) circuitry, particularly in carrier aggregation architectures, leading to linearity issues and degraded noise figure due to high impedance nodes and large voltage swings, which existing techniques struggle to mitigate effectively.
Innovation Solution
An N-path filter with multiple branches selectively coupled to a shared circuit node, incorporating a Miller amplifier and high pass filtering paths to generate impedance and prevent TX leakage from saturating the receiver, while allowing desired signals to pass through by adjusting impedance based on frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a high impedance node is used in the RX circuitry to amplify the received signal, then the signal amplification is improved, but TX leakage and jammers cause large voltage swings that saturate the output and degrade linearity
Solution Approach 1:
The receive signal path is divided into multiple N-path branches, each with its own feedback path. This segmentation allows the circuit to process different frequency components separately and apply appropriate impedance control to each branch, preventing saturation from TX leakage while maintaining signal amplification.
Solution Approach 2:
The patent employs dynamic impedance control at the common node of the feedback paths. By adjusting the impedance state (high or low) based on the detected signal frequency, the circuit adaptively prevents TX leakage saturation during certain phases while allowing signal amplification during other phases, resolving the contradiction between amplification and saturation.
2Ease of manufacture
If conventional filtering techniques are used to reject TX leakage, then the implementation simplicity is maintained, but the filtering order is insufficient to achieve adequate rejection in carrier aggregation architectures
Solution Approach 1:
The patent implements feedback paths in each N-path branch that feed a portion of the output signal back to the input. This feedback mechanism creates an effective high-order filtering response that enhances TX leakage rejection while maintaining implementation feasibility through the structured feedback architecture.
Solution Approach 2:
The N-path filter utilizes periodic switching of the multiple branches, where each branch is activated in sequence during different time phases. This periodic action across multiple branches synthesizes a high-order filtering effect that provides adequate TX leakage rejection while keeping each individual branch relatively simple to implement.
3Measurement precision
If the LNA output is configured as a high impedance node to maintain signal integrity, then the signal-to-noise ratio is improved, but linearity issues arise due to large blocker swing from TX leakage and jammers
Solution Approach 1:
The patent dynamically adjusts the impedance at the common node between high and low states based on the operating phase and detected frequency. During phases when TX leakage or jammers are present, the impedance is lowered to reduce voltage swing and maintain linearity. During signal reception phases, the impedance is raised to improve signal-to-noise ratio, thus dynamically resolving the contradiction between these two requirements.
Solution Approach 2:
The circuit changes the impedance parameter of the common node based on the frequency of the received signal. By detecting whether the signal is at a first frequency (TX leakage/jammer) or second frequency (desired signal), the circuit adjusts the impedance parameter accordingly, optimizing both linearity and signal-to-noise ratio under different operating conditions.
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 solution effectively rejects TX leakage and jammers, maintaining sensitivity and achieving high-order filtering, thereby improving noise figure and linearity in RX circuitry, even in concurrent carrier aggregation operations.
Implementation Method 1
an amplifier (e.g., a Miller amplifier or an amplifier based on Miller effect) having an input coupled to an input voltage and a first capacitor coupled to both the input voltage and an output of the Miller amplifier
Data Source
AI summary
An N-path filter with one or more branches selectively coupled to a shared circuit node includes a first branch having a first feedback path and a second feedback path. The first feedback path includes a Miller amplifier having an input coupled to an input voltage and a first capacitor coupled to both the input voltage and an output of the Miller amplifier. The second feedback path includes a node in common with the first feedback path. The second feedback path also includes a first high pass filter coupled to the output of the Miller amplifier and a second capacitor coupled to both the first capacitor and the first high pass filter.