Low-Noise Amplifier Topology for SAW-Less Receiver Linearity
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Solution Overview
Problem
In cellular communication, SAW-less receivers face challenges in reducing chip area and maintaining linearity due to strong blockers, which induce voltage swings and affect circuit operations.
Innovation Solution
A low noise amplifier (LNA) design comprising Gm cells, assistant circuits, and adders, along with a detect and control circuit, is used to generate differential output pairs and dynamically enable/disable assistant circuits based on blocker presence to manage noise and linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a SAW filter is used to filter out large blockers, then the receiver can maintain linearity, but the receiver cost increases and chip area is occupied
Solution Approach 1:
The patent extracts and removes the SAW filter from the receiver architecture, replacing it with a digital blocking cancellation mechanism implemented in the baseband processor. This eliminates the need for the physical filter component while maintaining the functionality of blocking large interferers, thus reducing chip area while preserving receiver linearity.
Solution Approach 2:
The patent replaces the mechanical/physical SAW filter with a digital signal processing approach. The digital blocking cancellation algorithm processes the received signal in the digital domain to cancel out large blockers, substituting the physical filtering mechanism with a computational one, thereby eliminating the need for additional hardware components.
2Reliability
If a passive filter is used to filter out strong blockers in a SAW-less receiver, then linearity can be maintained, but the chip area of the passive filter increases
Solution Approach 1:
The patent extracts the blocking function from the RF front-end passive filter and relocates it to the digital baseband processor. By implementing blocking cancellation digitally, the patent eliminates or minimizes the need for large passive filters in the RF path, thus maintaining linearity while significantly reducing chip area.
Solution Approach 2:
The patent substitutes the passive filter's mechanical filtering action with a digital signal processing algorithm. The digital blocking cancellation mechanism uses computational methods to identify and cancel large blockers, replacing the physical filter's function with a software-based solution that requires minimal hardware resources.
3Measurement precision
If the assistant circuits are always enabled to cancel noise, then the signal-to-noise ratio is improved, but the device complexity and power consumption increase
Solution Approach 1:
The patent implements dynamic control of the assistant circuits through a detect and control circuit that monitors the presence of large blockers in real-time. Based on the detection results, the control circuit dynamically adjusts the gain of the assistant circuits or enables/disables them, optimizing the signal-to-noise ratio while minimizing unnecessary circuit activity and associated complexity.
Solution Approach 2:
The patent employs a feedback mechanism where the detect and control circuit continuously monitors the input signal for large blockers and adjusts the assistant circuit operation accordingly. This feedback loop ensures that noise cancellation is applied only when necessary, reducing overall device complexity and power consumption while maintaining high signal-to-noise ratio performance when needed.
Data Source
AI summary
A low noise amplifier is used to amplify a differential input pair to generate a differential output pair. The low noise amplifier includes two main paths, two assistant circuits and two adders to make noise carried on two output signals of the differential output pair be the same; therefore, the noise of the two output signals can be fully cancelled in the following operations.