Local Oscillator Frequency Shifting for NF and Spur Isolation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing wireless communication systems face noise figure (NF) degradation due to difficulty in achieving proper isolation between local oscillator (LO) frequencies for different subscribers, particularly in small footprint implementations and when supply and ground nodes are shared, leading to issues like high NF degradation and spur interference.
Innovation Solution
Implementing dynamic frequency shifting by applying a low intermediate frequency (LIF) offset to separate LO frequencies for different subscribers, determining the need for an offset based on frequency separation thresholds and applying de-rotation in the digital domain to mitigate NF degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If LO frequencies for different subscribers are kept close together to save frequency resources, then frequency resource utilization is improved, but noise figure degradation and spur interference increase due to insufficient isolation
Solution Approach 1:
The patent implements dynamic frequency shifting where the LO frequency for one subscriber is adjusted based on the LO frequency of another subscriber. The frequency shift amount is determined dynamically by comparing the requested LO frequency with the current LO frequency of the other subscriber, ensuring adequate separation when needed while allowing closer frequencies when isolation is not an issue.
Solution Approach 2:
The patent changes the frequency parameter of the LO signal by applying a frequency offset. The offset is calculated based on the frequency difference between LO signals of different subscribers, and the LO frequency is tuned to a new value that ensures sufficient isolation to prevent NF degradation while optimizing frequency resource usage.
2Object-affected harmful factors
If LO frequencies for different subscribers are separated by a large offset to prevent NF degradation, then noise figure performance is improved, but frequency resource utilization deteriorates
Solution Approach 1:
The frequency separation is not fixed but dynamically adjusted based on the specific frequency allocation. The system calculates the required offset based on the requested LO frequency and the LO frequency of the other subscriber, applying the minimum necessary separation to prevent NF degradation while maximizing frequency resource efficiency.
Solution Approach 2:
The LO frequency parameter is adjusted by a variable offset rather than a fixed large separation. The offset magnitude is determined by the frequency difference between subscribers' LO signals, allowing the system to maintain adequate isolation only when necessary, thereby improving overall frequency resource utilization.
3Device complexity
If the same supply and ground nodes are shared between LO signals to reduce circuit complexity, then device complexity is reduced, but isolation between LO frequencies becomes insufficient leading to spur interference
Solution Approach 1:
The patent extracts the frequency separation function from the physical circuit isolation and implements it through frequency domain management. Instead of requiring separate supply and ground nodes for each LO signal, the system separates the LO frequencies in the frequency domain by applying dynamic frequency offsets, thereby preventing spur interference while maintaining shared circuit resources.
Solution Approach 2:
The patent introduces a frequency offset mechanism as an intermediary between the shared circuit resources and the LO signals. This intermediary layer manages the frequency allocation dynamically, ensuring that even when LO signals share the same physical nodes, their frequency separation prevents harmful interactions and spur generation.
Data Source
AI summary
Certain aspects of the present disclosure are directed towards methods and apparatus for wireless communication. An example method generally includes: comparing a requested local oscillator (LO) frequency for a first LO signal of a first subscriber with an LO frequency for a second LO signal of a second subscriber, determining a frequency offset for the first LO signal based on the comparison, and tuning a frequency of the first LO signal based on the requested LO frequency and the frequency offset.