Linear RF Transmitter Training With Inverse Exponential Test Signal
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Solution Overview
Problem
Existing RF transmitters face challenges in accurately detecting the onset of compression in RF power amplifiers during level training due to non-perfect integrator behavior of loop filters, particularly when the first pole is at a frequency higher than zero, leading to inaccurate detection and potential false compression alerts.
Innovation Solution
A linear RF transmitter design that employs a test signal with an inverse exponential relationship to maintain a constant output voltage before compression, allowing for precise detection of the compression point, even with a low pass filter having a first pole at a frequency greater than zero, and is suitable for wideband modulation protocols like TETRA 2, HPD, and WiMax.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the loop filter is designed with a first pole at a low frequency and second pole and zero at higher frequencies, then the loop stability is improved, but the level training accuracy deteriorates due to non-perfect integrator behavior
Solution Approach 1:
The patent changes the test signal parameters from a conventional linear ramp to an inverse exponential form. This parameter change compensates for the non-perfect integrator behavior introduced by the loop filter poles, allowing accurate compression point detection while maintaining the stable loop filter design with first pole at low frequency and second pole/zero at higher frequencies.
Solution Approach 2:
The inverse exponential test signal acts as an intermediary that bridges the gap between the stable but non-ideal loop filter and the compression detection requirement. By using this specially shaped test signal, the system can achieve accurate level training despite the loop filter's non-perfect integrator characteristics.
2Adaptability or versatility
If the first pole of the loop filter is placed at a frequency greater than zero, then the wideband modulation performance is improved, but the compression detection accuracy deteriorates due to loss of perfect integrator behavior
Solution Approach 1:
The patent applies parameter changes to the test signal waveform, using an inverse exponential form that specifically compensates for the effects of having the first pole at a non-zero frequency. This allows the system to maintain both wideband modulation capability and accurate compression detection.
Solution Approach 2:
The inverse exponential test signal is designed in advance to counteract the non-integrator effects of the loop filter. By applying this pre-calculated compensating waveform, the system prevents the degradation of compression detection accuracy that would otherwise result from the first pole being at a frequency greater than zero.
3Ease of operation
If a conventional linear ramp test signal is used for level training, then the procedure is simple, but false compression alerts occur due to non-perfect integrator behavior of the loop filter
Solution Approach 1:
The patent modifies the test signal parameter from a linear ramp to an inverse exponential waveform. This change eliminates false compression alerts while maintaining the automated level training procedure, thereby improving reliability without significantly complicating the operation.
Solution Approach 2:
The inverse exponential test signal generation incorporates feedback principles where the expected loop filter response is used to determine the appropriate test signal shape. This ensures that the test signal automatically compensates for the loop filter's non-perfect integrator behavior, preventing false compression detection.
Data Source
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.