Linear RF Transmitter Training for Accurate Compression Detection
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Solution Overview
Problem
Existing RF transmitters face difficulties in accurately identifying the appropriate strength level during level training to avoid compression of the RF power amplifier, particularly when the loop filter is not a perfect integrator, leading to potential false detection of compression and instability in wideband modulation applications.
Innovation Solution
A linear RF transmitter with a test signal generator that applies a voltage test signal increasing in an inverse exponential manner, allowing the output signal to remain constant before compression, enabling accurate detection of the compression point and avoiding false detection, even with a low pass filter having a first pole at a frequency higher than zero Hz.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a loop filter with a first pole at a low frequency and second pole and zero at higher frequencies is used, then the bandwidth of the loop is constrained and stability is ensured, but the loop filter is no longer a perfect integrator which causes difficulty in identifying the appropriate strength level during level training to avoid compression of the RFPA
Solution Approach 1:
The patent changes the waveform parameters of the test signal from a conventional linear ramp to an inverse exponential waveform. This parameter change compensates for the integration error introduced by the loop filter's non-ideal characteristics, allowing accurate compression point detection even when the loop filter has a first pole at a frequency higher than zero Hz.
2Reliability
If the maximum limit of training is set at a level known to be below the clip point, then false detection of compression is avoided, but the signal strength may be set too conservatively which reduces transmitter efficiency
Solution Approach 1:
The patent replaces the conventional linear ramp test signal with an inverse exponential waveform that mathematically compensates for the loop filter's integration characteristics. This substitution enables precise identification of the actual compression point, allowing the maximum training limit to be set closer to the true clip point without causing false detection, thereby improving transmitter efficiency while maintaining reliability.
3Ease of operation
If a linear ramp test signal is used during level training, then the training process is simple, but the output signal increases continuously which makes it difficult to accurately identify the compression point when the loop filter is not a perfect integrator
Solution Approach 1:
The patent employs an inverse exponential waveform that can be generated through periodic integration of a decaying exponential function. This approach maintains the simplicity of automated training while achieving constant output signal during the linear region of RFPA operation, enabling accurate compression point identification even with non-ideal loop filters.
Data Source
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AI summary
A linear RF transmitter (100) includes a forward path including a baseband signal combiner (109) and an RF (radio frequency) power amplifier (123), and a linearizing control loop from an output (127) of the RF power amplifier to an input of the combiner (109). A feedback control path (105, 107) of the loop delivers a baseband error control signal to the combiner. The transmitter further includes a test signal generator (102) to apply to the combiner in a closed loop level training mode a test signal comprising a voltage Vin which increases with time in a non-linear manner approaching an asymptotic limit such that in response an output signal produced by the combiner is a voltage Ve which is substantially constant over a period of time.