LNA Circuit for Out-of-Band Transmitter Self-Interference Cancellation
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Solution Overview
Problem
Wideband RF transceivers face significant challenges due to out-of-band-modulated transmitter self-interference, including cross-modulation and second-order inter-modulation, which conventional narrowband receivers do not encounter, necessitating effective interference reduction methods.
Innovation Solution
The implementation of a circuit comprising a common source transistor and a common gate transistor, along with a variable phase rotator and variable gain amplifier, to inject a transmitter replica signal and cancel out transmitter leakage by adjusting the phase and gain to eliminate interference at the input of the low noise amplifier.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If wideband receiver front-ends are used to handle larger interference signals, then the receiver can process wideband signals, but transmitter self-interference including cross-modulation and second-order inter-modulation increases
Solution Approach 1:
The patent applies preliminary anti-action by injecting a replica of the transmitter signal into the receiver signal path before the interference fully develops. This replica signal is phase-adjusted and gain-controlled to preemptively counteract the transmitter self-interference, including cross-modulation and second-order inter-modulation products, thereby protecting the wideband receiver from these harmful effects
Solution Approach 2:
The patent uses copying by creating an accurate replica of the transmitter signal and injecting it into the receiver path. This copied signal serves as a reference that matches the interference characteristics, allowing the system to cancel out the transmitter self-interference through coherent subtraction while preserving the desired receiver signal
2Adaptability or versatility
If antenna/duplexer isolation is reduced to enable wideband operation, then frequency tuning range increases, but transmitter leakage into the receiver band increases
Solution Approach 1:
The patent creates a copy of the transmitter signal path and injects it into the receiver signal path. This replica signal accurately reproduces the transmitter leakage characteristics, enabling coherent cancellation of the unwanted transmitter signal that enters the receiver band due to reduced antenna/duplexer isolation
Solution Approach 2:
The patent introduces an intermediary signal path that copies the transmitter output and processes it through phase adjustment and gain control circuits. This intermediary replica acts as a mediator that enables the system to cancel transmitter leakage without requiring physical isolation improvements, thus maintaining wideband operation capability
Data Source
AI summary
Circuits for reducing out-of-band-modulated transmitter self-interference are provided. In some embodiments, receivers are provided, the receivers comprising: a low noise amplifier (LNA) having an input, a first output, and a second output, wherein the LNA includes: a common source transistor having a gate coupled to an input signal, a drain coupled to the first output of the LNA, and a source coupled to ground; and a common gate transistor having a gate coupled to a transmitter replica signal, a source coupled to the gate of the common source transistor, and a drain coupled to the second output of the LNA.