Split LNA Receiver with Digital Combining for Lower Noise Figure
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Solution Overview
Problem
Modern integrated CMOS transceivers in the WiFi range face limitations in noise figure due to integration into Si substrates and inherent CMOS technology limitations, leading to suboptimal receiver sensitivity and bandwidth utilization.
Innovation Solution
A split LNA configuration with a shared input matching network is used, where two or more LNAs are connected to the same antenna, each with separate down-convert mixers and baseband filters, and their outputs are digitally summed to improve signal-to-noise ratio and reduce noise figure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single LNA is integrated into CMOS transceiver, then device complexity is reduced and cost is lowered, but noise figure deteriorates to 4-5 dB due to inherent CMOS limitations
Solution Approach 1:
The LNA function is segmented into multiple parallel LNAs (first LNA, second LNA, etc.) that process signals independently and then combine their outputs digitally. This segmentation allows each LNA to contribute to the overall signal while adding diversity that improves noise figure beyond what a single CMOS LNA can achieve.
Solution Approach 2:
Multiple LNA outputs are merged through digital combining at the baseband stage. The complex baseband signals from different LNAs are summed coherently, combining the signal components while the noise components add in a way that improves the overall signal-to-noise ratio and reduces noise figure.
2Reliability
If multiple LNAs with separate down-convert mixers are used, then noise figure is improved by 1 dB, but device complexity and circuit area increase
Solution Approach 1:
Multiple LNAs share common functionality in the digital baseband processing stage. The same filtering, mixing, and combining operations are applied to outputs from different LNAs, allowing the system to achieve improved noise figure while reusing circuit blocks across multiple signal paths.
Solution Approach 2:
A digital combining stage acts as an intermediary between the analog LNA outputs and the baseband processing. This digital mediator coherently combines the complex baseband signals from multiple LNAs, enabling noise figure improvement while maintaining a structured and manageable system architecture.
3Ease of manufacture
If integration is performed on Si substrate, then manufacturing cost is reduced, but noise figure is limited to 4-5 dB due to substrate losses
Solution Approach 1:
The system replaces analog signal combining (which would be lossy on Si substrate) with digital signal combining. By converting LNA outputs to digital baseband signals and performing combination in the digital domain, the patent avoids the losses inherent in analog RF combining on silicon substrates, thereby achieving better noise figure while maintaining CMOS integration benefits.
Data Source
AI summary
Systems and methods of reducing SNR and increasing bandwidth of received signals are disclosed. LNAs receive signals from an antenna via a common input matching network. The amplified signals are downconverted, filtered and digitized before being coherently combined at a DSP. Depending on the LO frequencies used by mixers in the different receiver paths, the combined signals reduce the SNR when the LO frequencies are the same by reducing the non-correlated noise introduced by the LNAs or increase the bandwidth processed when the LO frequencies are different. The bandwidths are contiguous or non-contiguous.