Noise-Cancelling Receiver Blocker Filtering via Anti-Phase Coupling
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Solution Overview
Problem
Noise-cancelling receiver front ends in RF communications face challenges in improving out-of-band interferer rejection and linearity due to the use of capacitors, which lower input impedance peaking frequency and consume significant on-chip area.
Innovation Solution
The implementation of additional mixers in parallel with existing mixers, along with anti-phase coupling and cross-coupling capacitors, to enhance noise cancellation and blocker filtering, reducing the need for capacitors and improving linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If capacitors are provided to bypass undesired signal components in noise-cancelling architecture, then noise and out-of-band interferer rejection is improved, but input impedance peaking frequency is lowered and TIA linearity is degraded
Solution Approach 1:
The patent introduces an intermediary blocking capacitor coupled between the first and second signal paths at the mixer output stage. This blocking capacitor selectively prevents out-of-band interferers from coupling between paths while allowing desired in-band signals to pass through, thereby improving interferer rejection without degrading TIA linearity for legitimate signals
Solution Approach 2:
The patent segments the noise cancellation function into two distinct stages: (1) differential mixing in separate signal paths with individual noise cancellation, and (2) post-mixing blocking of out-of-band interferers via the blocking capacitor. This segmentation allows each stage to optimize its specific function without compromising the other
2Object-affected harmful factors
If capacitors are provided to bypass undesired signal components, then noise cancellation performance is improved, but on-chip area is significantly consumed
Solution Approach 1:
The patent extracts the out-of-band interferer blocking function from the traditional large capacitor-based noise cancellation approach and implements it separately using a small blocking capacitor at the mixer output. This extraction allows the main noise cancellation capacitors to be minimized while still achieving effective interferer rejection through the dedicated blocking stage
Solution Approach 2:
The patent changes the operational parameters by placing the blocking capacitor at the mixer output rather than at the LNA input, and by configuring it to block only out-of-band frequencies while passing in-band signals. This parameter change enables effective interferer rejection with a much smaller capacitor value, reducing on-chip area consumption
3Object-affected harmful factors
If capacitors are provided to bypass common mode signal components, then common mode rejection is improved, but input impedance peaking frequency is lowered
Solution Approach 1:
The blocking capacitor acts as an intermediary element that specifically targets out-of-band common mode interferers at the mixer output stage. By positioning it after the mixing stage, it rejects common mode components without affecting the input impedance characteristics and peaking frequency of the TIA, which are determined by earlier stages
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 approach effectively cancels noise and out-of-band interferers, increases the input impedance peaking frequency, and reduces on-chip area requirements, thereby enhancing the performance of noise-cancelling receiver front ends.
Implementation Method 1
a noise-cancelling architecture may include capacitors coupled to the mixer outputs to bypass undesired differential mode signal components
Implementation Method 2
additional mixers in parallel with existing mixers, along with anti-phase coupling and cross-coupling capacitors, to enhance noise cancellation and blocker filtering
Data Source
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AI summary
Techniques for improving rejection of out-of-band interference in a noise-cancelling receive architecture. In an aspect, capacitors blocking in-band signals and passing through out-of-band signals destructively couple an auxiliary mixer output to a mixer output. In a further aspect, cross-coupling capacitors are provided to couple a first signal path with a second signal path of the noise-cancelling receive signal path. Baseband poly phase cross-coupling blocker filtering is further provided for out-of-band interference cancellation to create notch responses at blocker offset frequencies. The techniques disclosed may readily be adapted for multi-phase local oscillator systems.