Local Oscillator Using Spectral Replicas to Avoid Frequency Pulling
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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 filtering to avoid spectral emission mask violations and injection locking issues, especially in high-frequency bands like 5 GHz.
Innovation Solution
The implementation of a local oscillator generation mechanism with a non-integer multiplication ratio between the local oscillator and RF frequencies, using digital techniques such as all-digital phase locked loops (ADPLL) and XOR operations, to generate I and Q square waves, thereby avoiding frequency pulling and reducing the need for stringent band pass filters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If an integer multiplication ratio is used between local oscillator and RF frequencies, then the circuit design is simpler, 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 frequency pulling effects while maintaining manageable circuit complexity through the use of spectral replicas and filtering techniques.
2Reliability
If stringent band pass filters are used to avoid frequency pulling, then frequency stability is improved, but device complexity and cost increase
Solution Approach 1:
By changing the multiplication ratio to a non-integer value, the patent eliminates the need for stringent band pass filters. The frequency stability is achieved through the non-integer ratio itself, which prevents RF signal interference from causing frequency pulling, rather than relying on complex filtering.
Solution Approach 2:
The patent extracts and eliminates the need for complex band pass filters by using a non-integer multiplication ratio. The harmful frequency pulling effect is removed at its source through the frequency relationship design, rather than requiring additional filtering components.
3Object-affected harmful factors
If spectral replicas are used with non-integer multiplication ratio, then frequency pulling is eliminated, but spectral spurs are generated
Solution Approach 1:
The patent converts the potentially harmful spectral replicas into a beneficial solution. By using a non-integer multiplication ratio (3/2), the spectral replicas are positioned such that they eliminate frequency pulling effects. The filtering requirement is relaxed because the replicas naturally fall outside the desired frequency band, turning what could be harmful interference into a protective mechanism.
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. An input baseband signal is interpolated and upconverted in the digital domain to an IF. The LO operates at a frequency which is a n/m division of the target RF frequency fRF. The IF frequency is configured to ½ of the LO frequency. The upconverted IF signal is then converted to the analog domain via digital power amplifiers followed by voltage combiners. The output of the combiners is band pass filtered to extract the desired replica.