Band-Split LO Amplification for Reduced Harmonic Generation
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Solution Overview
Problem
Local oscillator signals, when amplified, introduce harmonics that are difficult to filter and can degrade receiver performance, especially in wide bandwidth applications, due to non-linear amplifier operation and the challenge of implementing tunable filters with sharp cut-off frequencies on integrated circuits.
Innovation Solution
A system that splits the local oscillator signal into multiple bands, amplifies and filters each band separately, and combines the outputs to generate a 'clean' signal with reduced harmonics, using passive components to avoid introducing additional harmonics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the local oscillator signal is amplified to improve signal strength for mixing, then the LO signal level is improved, but harmonics are generated that degrade receiver performance
Solution Approach 1:
The frequency range is divided into multiple non-overlapping bands, with each band processed by a dedicated amplifier and filter combination. This segmentation allows each amplifier to operate in its linear region for its specific band, avoiding harmonic generation while maintaining adequate signal level, and enables simple fixed-frequency filters to remove harmonics effectively
Solution Approach 2:
The system dynamically selects which band processing path to use based on the current LO frequency, using control logic that determines the appropriate band and enables only that specific amplifier and filter path. This dynamic switching ensures the correct band processing is applied without introducing harmonics from other bands
2Object-generated harmful factors
If a tunable filter with sharp cut-off frequencies is implemented to remove harmonics, then harmonic rejection is improved, but device complexity and difficulty of integration increase
Solution Approach 1:
Instead of using a single complex tunable filter, the frequency range is segmented into multiple bands, each with its own simple fixed-frequency filter. This allows the use of straightforward RC or LC filters with fixed cut-off frequencies that are easy to integrate, rather than requiring a complex tunable filter with dynamically adjustable sharp cut-offs
Solution Approach 2:
The patent uses simple, inexpensive fixed-frequency filters (RC or LC networks) that can be easily integrated on-chip, replacing the need for complex, expensive tunable filters. These simple filters are sufficient because each operates at a fixed frequency optimized for its specific band
3Device complexity
If a single amplifier is designed to cover the entire frequency range, then device complexity is reduced, but non-linear operation occurs that generates harmonics
Solution Approach 1:
The frequency range is divided into multiple non-overlapping bands, with each band having its own dedicated amplifier. Each amplifier is designed to operate only in its specific frequency band, allowing it to maintain linear operation and avoid generating harmonics. The overall system covers the wide frequency range through the combination of multiple specialized amplifiers
Solution Approach 2:
Each amplifier is optimized for its specific frequency band with appropriate biasing and component values, ensuring linear operation locally in that band. This local optimization allows each amplifier to maintain low distortion and avoid harmonic generation in its operating range, whereas a single amplifier would have to compromise across the entire wide bandwidth
Data Source
AI summary
Techniques for reducing harmonics of a local oscillator (LO) signal. A methodology implementing the techniques according to an embodiment includes splitting an LO signal into first and second LO signals using a passive splitting circuit. The method also includes generating one of either a first enable signal or a second enable signal based on the LO signal frequency. The method further includes amplifying and filtering the first LO signal to generate a first band LO signal, in response to the first enable signal, and amplifying and filtering the second LO signal to generate a second band LO signal, in response to the second enable signal. The method further includes combining, using a passive Wilkinson combiner, output paths of the first band processing circuit and the second band processing circuit to provide either the first band LO signal or the second band LO signal as a reduced harmonic LO signal.