Direct-Conversion Receiver IM2 Noise Cancellation Circuit
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Solution Overview
Problem
Direct-conversion receivers in mobile handsets suffer from second-order intermodulation (IM2) noise, particularly due to down-conversion mixers, which cause interference and degrade receiver performance by generating unwanted differential and common mode IM2 components.
Innovation Solution
A noise cancellation system comprising a noise correction circuit with an amplifier stage, a second-order noise reduction stage, and a feedback loop stage, utilizing adjustable resistors and a buffer to cancel differential and common mode IM2 noise, thereby reducing IM2 noise without affecting the dc offset.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a direct-conversion receiver is used in a mobile handset, then the receiver structure is simplified and bulky components are eliminated, but second-order intermodulation (IM2) noise is generated by the down-conversion mixer which degrades receiver performance
Solution Approach 1:
The patent converts the harmful IM2 noise into a useful cancellation signal by injecting a synthesized IM2 component into the signal path. The synthesized noise is created to match the characteristics of the actual IM2 noise, then used to cancel the harmful interference through destructive interference, thereby transforming the harmful effect into a beneficial noise cancellation mechanism
Solution Approach 2:
The patent introduces an intermediary IM2 cancellation circuit that acts as a mediator between the down-conversion mixer and the receiver output. This intermediary circuit synthesizes and injects a cancellation signal that interferes destructively with the harmful IM2 noise, effectively mediating the conflict between simplified receiver structure and noise performance
2Reliability
If traditional noise filtering methods are used to reduce IM2 noise, then receiver performance may be improved, but the design becomes more complex with additional filtering stages
Solution Approach 1:
Instead of using complex filtering stages to remove IM2 noise, the patent converts the harmful noise into a beneficial cancellation signal. By synthesizing and injecting a matched IM2 component, the system achieves noise reduction through destructive interference rather than filtering, maintaining simple design while improving performance
Solution Approach 2:
The patent changes the approach from frequency-domain filtering to time-domain signal manipulation. By adjusting the phase and amplitude parameters of the synthesized IM2 cancellation signal, the system achieves noise reduction without requiring additional filtering hardware, thus maintaining design simplicity while improving receiver performance
Data Source
AI summary
A noise cancellation system comprises a first noise cancellation apparatus configured to process an I-channel signal, wherein an I-channel differential mode second-order intermodulation component and an I-channel common mode second-order intermodulation component cancel each other in the first noise cancellation apparatus and a second noise cancellation apparatus configured to process a Q-channel signal, wherein a Q-channel differential mode second-order intermodulation component and a Q-channel common mode second-order intermodulation component cancel each other in the second noise cancellation apparatus.