Down-Conversion Mixer Linearity for Weak Signal Extraction
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Solution Overview
Problem
Conventional wireless communication systems face challenges in extracting weak signals due to interference from strong unwanted signals, particularly in the presence of RF transmit signal leakage that contaminates received RF signals, leading to errors in signal processing.
Innovation Solution
A highly linear and low-noise down-conversion mixer is implemented, utilizing a source follower circuit and switching circuit to down-convert RF signals, with a coupling capacitor that adjusts gain and linearity, and additional filtering to attenuate higher frequency components, effectively separating desired signals from strong unwanted signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If RF signals are amplified in preparation for transmission, then transmission power is improved, but strong RF transmit signals leak to receiver circuitry causing blocking and interference
Solution Approach 1:
The receiver signal path is segmented into multiple processing stages: a first down-conversion mixer for initial frequency translation, a first filter for selective frequency component removal, and a second down-conversion mixer for final baseband conversion. This segmentation allows targeted filtering of leaked transmit signals at intermediate stages while preserving weak received signals.
Solution Approach 2:
A first local oscillator signal is introduced as an intermediary element to facilitate the first down-conversion stage. This intermediary frequency translation enables the insertion of a first filter that can selectively remove transmit signal frequencies before they reach subsequent processing stages, effectively mediating between the high-power transmit path and the sensitive receive path.
2Device complexity
If conventional down-conversion mixers are used, then signal processing is simplified, but weak signals cannot be extracted in the presence of very strong unwanted signals
Solution Approach 1:
The first down-conversion mixer performs preliminary frequency translation of the received RF signal to an intermediate frequency before subsequent filtering and processing. This preliminary action separates the desired signal from strong unwanted transmit signals in the frequency domain, enabling more effective filtering and improving weak signal extraction accuracy before final baseband conversion.
Solution Approach 2:
The system employs dynamic filtering where the first filter is configured to selectively remove specific frequency components corresponding to leaked transmit signals while preserving the down-converted desired signal. This dynamic frequency-selective filtering adapts to the specific frequency relationships between transmit and receive signals, enabling effective rejection of strong unwanted signals while maintaining weak signal integrity.
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
This solution enables the extraction of weak signals with improved linearity and reduced noise, minimizing interference from strong transmitter signals, thereby enhancing the accuracy of signal processing in wireless communication systems.
Implementation Method 1
The switching circuit may be enabled to down-convert the communicated output RF voltage signals to generate differential baseband signals
Implementation Method 2
The differential output signal from the switching circuit may be filtered to attenuate higher frequency components
Data Source
AI summary
A method and system for wireless communication is provided and may include mitigating blocker signals in transmitted RF signals in a wireless device including a transmitter front end. The mitigation may include up-converting a baseband signal, mixing the up-converted baseband signal with a feedback signal, and amplifying the mixed up-converted baseband signal and the feedback signal to generate an output signal. The feedback signal may be generated by down-converting the output signal, low-pass filtering the down-converted output signal, and up-converting the filtered down-converted signal for the summing. The blocker signals may correspond to receive frequencies for the wireless device and may be converted to DC via the down-converting. The wireless devices may operate in accordance with at least a CDMA standard. The mixed up-converted baseband signal and the feedback signal may be amplified utilizing a source follower amplifier, where the gain and/or linearity may be configured by varying coupling capacitors.