Spread-Spectrum PID Testing Signal Separation
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Solution Overview
Problem
Passive inter-modulation distortion (PID) in RF communications systems is challenging to measure accurately due to interference from signals that are close in frequency to the PID signals, making it difficult to distinguish PID levels, especially when testing components with non-linearities such as inconsistent metal-to-metal contacts, which can degrade the entire RF communications system performance.
Innovation Solution
The method involves using spread-spectrum excitation signals, generated by applying a pseudo-random code sequence to continuous wave signals, to test devices under test, where the output signals are down-converted and de-spread, effectively separating PID signals from interfering signals by spreading the interfering signals out in bandwidth, allowing for more accurate measurement of PID levels without the need for expensive shielded testing environments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional PID measurement methods are used, then the measurement process is simple, but the measurement precision is poor due to interference from signals close in frequency to PID signals
Solution Approach 1:
The patent applies parameter changes by transforming the excitation signal from traditional continuous wave to spread spectrum signal. This changes the frequency domain characteristics of the signal, spreading the energy over a wide bandwidth. The PID products generated from spread spectrum excitation can be distinguished from interfering signals through correlation processing, significantly improving measurement precision without requiring complex shielded environments
Solution Approach 2:
The patent introduces spread spectrum coding as an intermediary mechanism between the excitation signal and the measurement process. By applying pseudo-random code sequences to modulate the excitation signal, the system creates a unique signature for the PID products. This intermediary coding scheme enables the measurement system to distinguish desired PID signals from interfering signals through correlation detection, improving precision while maintaining manageable system complexity
2Measurement precision
If shielded testing environments are used to eliminate interference, then the measurement accuracy improves, but the testing cost increases significantly
Solution Approach 1:
Instead of changing the physical environment (shielded rooms), the patent changes the signal parameters by using spread spectrum modulation. This approach achieves interference rejection through signal processing rather than physical isolation, eliminating the need for expensive shielded testing environments while maintaining high measurement accuracy
Solution Approach 2:
The patent converts the presence of interfering signals from a harmful factor into a manageable condition. By using spread spectrum excitation and correlation processing, the system can distinguish desired PID products from interfering signals even in unshielded environments. The interference is not eliminated but rendered distinguishable and quantifiable, allowing accurate measurement without costly infrastructure
3Measurement precision
If spread-spectrum excitation signals are used, then the separation of PID signals from interfering signals improves, but the device complexity increases
Solution Approach 1:
The patent uses spread spectrum coding as an intermediary that simplifies the separation process. By embedding pseudo-random code sequences in the excitation signal, the system creates uniquely identifiable PID products. The correlation processor acts as a matched filter that automatically separates desired signals from interference based on code correlation, achieving excellent signal separation with relatively simple processing architecture
Solution Approach 2:
The patent applies preliminary action by pre-modulating the excitation signal with spread spectrum codes before applying it to the device under test. This preliminary coding prepares the signal in advance so that the subsequent measurement process only requires correlation detection, a computationally simple operation. The complex signal processing is performed offline during code generation, not during real-time measurement
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 significantly reduces the impact of interfering signals, enabling more precise measurement of PID levels and identifying devices with unacceptable performance, thus improving the accuracy of RF communications system testing and potentially eliminating the need for costly shielded rooms.
Implementation Method 1
spread-spectrum excitation signals, generated by applying a pseudo-random code sequence to continuous wave signals
Implementation Method 2
the output signals are down-converted and de-spread
Implementation Method 3
the output signals are down-converted and de-spread, effectively separating PID signals from interfering signals by spreading the interfering signals out in bandwidth
Data Source
AI summary
According to methods of performing a passive inter-modulation distortion (“PID”) test, a first excitation signal and a second excitation signal are applied to a device under test, where at least one of the first and second excitation signals is a spread spectrum excitation signal. An output signal is received that includes a PID signal generated from mixing of the first and second excitation signals. At least a portion of the output signal is de-spread. A characteristic of the PID signal may then be measured.