Dual Modulation Carrier Suppression in QPSK Transmitters
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Solution Overview
Problem
Residual carrier in modulated outputs causes interference and violates FCC regulations due to leakage from RF paths and amplitude imbalances in QPSK modulators, which existing technologies fail to adequately suppress.
Innovation Solution
A system and method utilizing a digital logic block to generate a cover sequence by removing transitions from input signals, which are then modulated with an RF carrier and used to enhance carrier suppression in a QPSK modulator, achieving dual modulation and significantly higher residual carrier suppression.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a mixer or modulator is used to perform frequency transition, then the signal can be modulated, but residual carrier leakage occurs and causes interference
Solution Approach 1:
The patent segments the modulation process into two distinct stages: a first modulator performs initial frequency transition, and a second modulator performs a second frequency transition. This segmentation allows each modulator to handle a portion of the modulation task, thereby reducing the residual carrier leakage from any single modulator while achieving the overall frequency transition goal.
2Manufacturing precision
If amplitude balance is maintained in QPSK modulator, then modulation accuracy improves, but residual carrier suppression is insufficient
Solution Approach 1:
The patent introduces an intermediary approach by using a cover sequence that is processed through digital logic to generate an altered cover sequence. This altered sequence acts as a mediator that, when combined with the original modulated signal, cancels out the residual carrier while maintaining modulation accuracy. The cover sequence serves as an intermediate element that enables both accurate modulation and carrier suppression.
3Productivity
If bandwidth is shared among users, then spectral efficiency improves, but residual carrier causes interference with other users
Solution Approach 1:
The patent employs a feedback mechanism where the output of the first modulator is fed into the second modulator. This feedback loop allows the system to continuously adjust and refine the modulation process, ensuring that residual carrier leakage is minimized while maintaining efficient bandwidth utilization. The feedback enables real-time correction of carrier leakage that would otherwise interfere with other users sharing the bandwidth.
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
The solution achieves residual carrier suppression of at least 40 dB to 60 dB, significantly higher than current solutions, effectively reducing interference and compliance with regulatory standards.
Implementation Method 1
The mixer may be configured to generate a modulated cover sequence by modulating a radio frequency (RF) carrier with the cover sequence
Implementation Method 2
The modulator may be further configured to receive the modulated cover sequence as an RF carrier input and generate an RF output by modulating the modulated cover sequence with the altered version first the first signal and the altered version of the second signal
Data Source
AI summary
Included are embodiments for enhanced carrier suppression. One embodiment of a circuit includes a mixer that receives a cover sequence, the cover sequence including transition data from a first signal and a second signal. The mixer may be configured to generate a modulated cover sequence by modulating a radio frequency (RF) carrier with the cover sequence. Some embodiments also include a modulator that is communicatively coupled to the mixer. The modulator may be configured to receive and modulate an altered version of the first signal and an altered version of the second signal. The modulator may additionally receive the modulated cover sequence as an RF carrier input and generate an RF output by modulating the modulated cover sequence with the altered version of the first signal and the altered version of the second signal.