Digital Local Oscillator Mixing to Avoid RF Frequency Pulling
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing local oscillator generation schemes in wireless transceivers are susceptible to RF signal interference, particularly frequency pulling due to unwanted RF signals, which complicates the design and requires stringent band-pass filtering, especially in high-frequency bands like 5 GHz for wideband signal transmission.
Innovation Solution
The implementation of a local oscillator generation mechanism with a non-integer multiplication ratio between the local oscillator and RF frequencies, utilizing digital logic and all-digital phase locked loops to generate I and Q square waves, thereby avoiding frequency pulling and reducing the need for stringent band-pass filtering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If an integer multiplication ratio is used between local oscillator and RF frequencies, then the oscillator can be simplified, but frequency pulling occurs due to RF signal interference
Solution Approach 1:
The patent changes the multiplication ratio parameter from an integer to a non-integer value (specifically 3/2 or 1.5). This parameter change eliminates the frequency pulling effect by ensuring the local oscillator frequency does not coincide with RF harmonics, while still maintaining a relatively simple oscillator design without requiring complex filtering
2Object-affected harmful factors
If a non-integer multiplication ratio is used between local oscillator and RF frequencies, then frequency pulling is avoided, but the oscillator design becomes more complicated
Solution Approach 1:
The patent uses a specific non-integer ratio of 3/2 (1.5) which provides a practical compromise. This ratio is simple enough to implement with basic frequency multiplication circuits while effectively avoiding frequency pulling. The patent demonstrates that this specific parameter value achieves both goals without requiring complex filtering or additional circuitry
3Object-affected harmful factors
If resonator frequency is set to avoid RF harmonics, then frequency pulling is reduced, but the system requires complicated converters at very high frequencies
Solution Approach 1:
Instead of adjusting the resonator frequency to avoid RF harmonics (the conventional approach), the patent inverts the approach by adjusting the local oscillator frequency to be a non-integer multiple of the RF frequency. This eliminates the need for complex high-frequency converters while still avoiding frequency pulling effects
Data Source
AI summary
A novel and useful apparatus for and method of local oscillator (LO) generation with non-integer multiplication ratio between the local oscillator and RF frequencies. The LO generation schemes presented are operative to generate I and Q square waves at a designated frequency while avoiding the well known issue of harmonic pulling. The signal is input to a synthesizer timed to a rational multiplier of the RF frequency fRF. The signal is then divided to generate a plurality of phases of the divided signal. A plurality of combination signals are generated which are then multiplied by a set of weights and summed to cancel out some undersired products. The result is filtered to generate the LO output signal.