Power Amplifier Saturation Correction via Fixed DC Signal
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Solution Overview
Problem
Power amplifiers in radiotelephones experience undesirable switching transients due to non-smooth or nonlinear ramp changes, leading to saturation issues that fail to meet ETSI switching spectrum specifications, particularly when the integrator circuit output exceeds the PA's maximum power capability.
Innovation Solution
A closed-loop power control circuit that samples feedback signals from the PA to apply a fixed dc signal when the PA is near saturation, compensating for saturation without detection, and automatically reduces output power during abnormal conditions like low battery voltage, ensuring desirable switching spectrums.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the integrator circuit output drives the PA beyond its maximum output power capability, then the PA output power reaches maximum level, but switching transients occur and ETSI switching spectrum specification is failed
Solution Approach 1:
The patent applies preliminary anti-action by detecting when the integrator output voltage approaches the maximum voltage level (VMAX) and preemptively adjusting the integrator output voltage to prevent it from exceeding VMAX. This is achieved by comparing the integrator output voltage with VMAX and reducing the integrator output voltage when it gets too close to VMAX, thereby preventing saturation-induced switching transients before they occur.
Solution Approach 2:
The patent implements feedback by continuously monitoring the integrator output voltage and using this information to adjust the integrator output voltage dynamically. The control circuit compares the integrator output voltage with the maximum voltage level VMAX and provides feedback to reduce the integrator output voltage when necessary, ensuring the PA operates within its linear region and avoids saturation.
2Power
If the integrator circuit output voltage ramps up to maximum voltage level, then the PA output power is maximized, but the integrator output voltage cannot fall quickly when VRAMP decreases, causing sharp drop in PA output power
Solution Approach 1:
The patent applies preliminary anti-action by preventing the integrator output voltage from reaching the maximum voltage level VMAX in the first place. By continuously monitoring and preemptively reducing the integrator output voltage when it approaches VMAX, the system avoids the situation where the voltage must fall sharply from maximum level, thereby preventing the associated switching transients and spectral regrowth.
3Speed
If the control slope of the power amplifier has an inflection point or is very steep, then the PA can respond quickly to VRAMP changes, but undesirable switching transients occur
Solution Approach 1:
The patent implements feedback by continuously monitoring the integrator output voltage and dynamically adjusting it to maintain optimal control slope. The control circuit uses feedback to ensure the integrator output voltage remains within the linear operating region of the PA, avoiding inflection points and excessively steep slopes that would cause switching transients, while still maintaining fast response to VRAMP changes.
Data Source
AI summary
A circuit and method for a saturation correction of a power amplifier (PA) is provided in order to maintain a desirable switching spectrum. The circuit includes a closed loop system that is responsive to a dynamic PA control signal known as VRAMP. The method samples a detector voltage that represents the output of the PA at the maximum voltage level of VRAMP. The sampled detector voltage is then reduced by a predetermined amount and applied as a fixed voltage PA control signal in the place of VRAMP. As a result, the closed loop system responds to the fixed voltage PA control signal to bring the PA out of saturation before VRAMP can begin a voltage decrease. Once the VRAMP voltage decreases, VRAMP is reapplied as a dynamic PA control signal in place of the fixed voltage control signal.