Wideband Quadrature LO Generation With Frequency-Based Path Switching
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Wideband quadrature signal generation in transmitters, such as 4G LTE systems, faces challenges in achieving good amplitude and phase balance for local oscillator (LO) signals, especially across a broad range of frequencies, leading to imperfect image rejection and spectral efficiency issues.
Innovation Solution
A circuit and method utilizing a combination of a frequency synthesizer, polyphase filter, and frequency divider to generate quadrature LO signals, with a selector choosing between the signals based on desired output frequencies, ensuring balanced amplitude and phase across a wide frequency range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a single quadrature signal generation method is used, then the circuit is simple, but amplitude and phase balance deteriorates across wide frequency ranges
Solution Approach 1:
The frequency range is segmented into multiple bands, with each band having a dedicated quadrature signal generation path optimized for that range. The system divides the wide frequency spectrum into separate operational zones, allowing each segment to be optimized independently for amplitude and phase balance while maintaining overall wideband coverage.
Solution Approach 2:
The system dynamically switches between different quadrature signal generation methods based on the desired output frequency. A frequency detector and selector circuit automatically choose the appropriate generation path (e.g., polyphase filter for lower frequencies, frequency divider for higher frequencies) to maintain optimal performance across the entire frequency range.
2Productivity
If frequency range is extended, then spectral efficiency improves, but amplitude and phase balance becomes harder to maintain
Solution Approach 1:
Each frequency band is assigned a specialized quadrature signal generation method with locally optimized characteristics. Lower frequency bands use polyphase filters optimized for their specific range, while higher frequency bands use frequency dividers, ensuring that each local frequency region achieves optimal amplitude and phase balance tailored to its requirements.
Solution Approach 2:
The system changes the operational parameters and generation methodology based on the target frequency. By detecting the desired frequency and selecting the appropriate generation path, the system adapts its parameters (filter coefficients, division ratios, etc.) to maintain precise amplitude and phase balance across the extended frequency spectrum.
3Reliability
If quadrature signal balance is improved, then image rejection improves, but circuit complexity increases
Solution Approach 1:
The system employs dynamic selection between different quadrature generation approaches based on frequency requirements. Rather than using a single complex circuit designed to handle all frequencies, the system dynamically switches between simpler, frequency-optimized paths, achieving high image rejection only when needed for each specific frequency band.
Solution Approach 2:
A frequency detector and selector circuit acts as an intermediary that analyzes the desired output frequency and routes the signal through the appropriate quadrature generation path. This intermediary component enables the system to achieve high image rejection by selecting the optimal generation method without requiring all paths to be simultaneously active, thus managing complexity.
Data Source
AI summary
Wide band quadrature signal generation includes a frequency synthesizer generating a LO or 2×LO signal, a polyphase filter coupled to receive the LO signal and generate first in-phase and quadrature LO signals, a 2:1 frequency divider coupled to receive the 2×LO signal and generate second in-phase and quadrature LO signals, and a LO signal selector for selecting either the first or second in-phase LO signals as an output in-phase LO signal and either the first or second quadrature LO signals as an output quadrature LO signal based on an output frequency. In some embodiments, when the output frequency is above a threshold, the first in-phase and quadrature LO signals are selected as the output in-phase and quadrature LO signals and when the output frequency is at or below the threshold, the second in-phase and quadrature LO signals are selected as the output in-phase and quadrature LO signals.