Local Oscillator Tuning for In-Band Intermodulation Control
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Solution Overview
Problem
Current wireless communication devices face challenges in meeting stringent spectral emission limits due to non-linearity in transmitters, leading to spurious emissions outside the assigned channel bandwidth, which can be costly to mitigate with high-linearity solutions.
Innovation Solution
The solution involves positioning the third-order intermodulation product within the assigned channel bandwidth by adjusting the local oscillator frequency and modulation frequency, allowing for compliance with out-of-band spurious emission limits without increasing transmitter linearity, thus enabling a lower-cost or simplified communication device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the transmitter uses high-linearity components to meet spectral emission limits, then spurious emissions are reduced, but device cost and complexity increase
Solution Approach 1:
The patent changes the frequency parameter of the local oscillator signal to position the third-order intermodulation product within the assigned channel bandwidth. By adjusting the local oscillator frequency, the intermodulation product frequency (which equals local oscillator frequency minus three times the modulation frequency) is shifted into the channel bandwidth, preventing it from appearing as a spurious emission outside the band.
Solution Approach 2:
Instead of treating the third-order intermodulation product as a harmful spurious emission to be suppressed, the patent converts it into a beneficial in-band signal. The intermodulation product is deliberately positioned within the channel bandwidth where it can be treated as useful signal energy rather than harmful interference, thereby eliminating the need for high-linearity components.
2Object-generated harmful factors
If the local oscillator frequency is changed to position the intermodulation product in-band, then spectral emission compliance is improved, but frequency stability requirements increase
Solution Approach 1:
The patent introduces dynamic frequency adjustment of the local oscillator based on the modulation frequency. The local oscillator frequency is made variable rather than fixed, allowing it to be tuned to different values depending on the modulation frequency to ensure the third-order intermodulation product remains positioned within the channel bandwidth under varying operating conditions.
Solution Approach 2:
The system employs feedback mechanisms to monitor and adjust the local oscillator frequency. By continuously monitoring the position of the intermodulation product and adjusting the local oscillator frequency accordingly, the system maintains compliance with spectral emission limits while adapting to changing modulation conditions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for easier compliance with stringent spectral emission limits, reducing the need for costly high-linearity transmitters and conserving power by minimizing frequency changes of the local oscillator signal, while maintaining efficient use of spectrum.
Implementation Method 1
a modulator arranged for converting in-phase and quadrature-phase components of a modulation signal at a modulation frequency to a radio frequency by mixing the in-phase and quadrature-phase components with the local oscillator signal
Data Source
AI summary
A wireless communication device (400) is arranged to transmit a transmission signal in an assigned channel bandwidth. The wireless communication device (400) comprises: a local oscillator (460) arranged to generate a local oscillator signal at a local oscillator frequency and a modulator (434) arranged for converting in-phase and quadrature-phase components of a modulation signal at a modulation frequency to a radio frequency by mixing the in-phase and quadrature-phase components with the local oscillator signal. The local oscillator frequency is arranged to place a third order intermodulation product having a frequency equal to the local oscillator frequency minus three times the modulation frequency within the assigned channel bandwidth.