Loopback Testing FDD Transmitter Distortion
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Solution Overview
Problem
In Frequency Division Duplex (FDD) systems, implementing loopback testing is challenging due to the need for additional switching circuitry to bypass transmit and receive filters, which increases cost and complexity, and affects system performance.
Innovation Solution
The solution involves degrading the linearity of the transmitter to generate distortion products, such as intermodulation products, within the receive frequency band, allowing for loopback testing without additional switching circuitry, by increasing the gain of amplifiers or reducing supply voltage, thereby creating test signals in the receive band.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If switching circuitry is added to bypass transmit and receive filters during testing, then loopback testing becomes possible, but device complexity and cost increase
Solution Approach 1:
The patent converts the harmful non-linear distortion products (intermodulation and harmonics) that are normally filtered out during regular operation into useful test signals. By intentionally generating these distortion products through non-linear amplification of test signals in the transmit band, the system creates signals that fall into the receive band, enabling loopback testing without requiring filter bypass switching circuitry.
Solution Approach 2:
The patent changes the operating parameters of the transmitter amplifier to operate in a non-linear region during testing, rather than maintaining optimal linear operation. This parameter change allows the generation of distortion products at specific frequencies that can be received and processed, enabling testing functionality without additional hardware.
2Adaptability or versatility
If switching circuitry is added to bypass filters, then testing can be performed, but system reliability decreases
Solution Approach 1:
The patent eliminates the need for switching circuitry by converting harmful distortion products into beneficial test signals. This removes the reliability concerns associated with additional switching components while maintaining full testing functionality.
Solution Approach 2:
The patent extracts the testing functionality from the normal signal path by using distortion products that naturally fall into the receive band, rather than requiring the test signals to pass through the filter switching mechanism. This separation eliminates the reliability impact of switching circuitry.
3Manufacturing precision
If transmitter linearity is maintained during normal operation, then communication quality is good, but test signal generation in receive band is not possible
Solution Approach 1:
The patent makes the transmitter dynamic by allowing it to switch between linear operation during normal communication and non-linear operation during testing. The transmitter can adapt its operating point to generate the required distortion products for testing while maintaining optimal linearity during regular operation, thus satisfying both requirements at different times.
Solution Approach 2:
The patent implements periodic switching between testing mode and normal operation mode. During testing intervals, the transmitter operates non-linearly to generate distortion products; during normal communication intervals, it operates linearly for optimal signal quality. This periodic alternation allows both testing capability and communication quality to be maintained.
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 method enables effective loopback testing of FDD systems without the need for bypassing filters, allowing for the testing of existing equipment and new designs, reducing costs and complexity, while maintaining system reliability and performance.
Implementation Method 1
If signals with frequencies f1 and f2 are generated in the transmit band and subjected to non-linear distortion, preferably after transmit filtering, intermodulation products will be generated, having frequencies fim = mf1 + nf2 where m and n are integers
Data Source
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AI summary
A communication device and method therein for loopback testing are provided. The device comprises a transmitter and a receiver and applies FDD for communication over one or more lines. The method comprises degrading a linearity of the transmitter, as compared to the linearity during normal operation. The method further 5 comprises transmitting at least one test signal in a transmit frequency band, such that at least one signal is created in a receive frequency band, wherein the created at least one signal is a distortion product of the at least one test signal; and further, receiving a response to the at least one created signal in the receive frequency band.