Envelope Tracking Waveform Control for RF Transmitter Ramp Periods
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Solution Overview
Problem
Existing envelope tracking techniques in RF transmitters fail to effectively address rapid gain and phase changes at low supply voltages, leading to phase distortion, and do not adequately manage transmit slot ramp-up and ramp-down periods in mobile radio designs, such as TDMA and CDMA systems.
Innovation Solution
A method and device that modify the power amplifier supply voltage by imposing a lower limit and providing a substantially constant voltage level during ramp periods, using a computation means to generate a waveform indicative of the modulated signal's envelope, ensuring the supply voltage remains above a predetermined value and maintaining linearity and efficiency, especially during ramp-up and ramp-down periods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the supply voltage is reduced to improve efficiency, then power consumption decreases, but rapid gain and phase changes occur causing phase distortion
Solution Approach 1:
The patent applies preliminary action by pre-distorting the I and Q values before modulation to compensate for the rapid gain and phase changes that occur at low supply voltages. This pre-compensation ensures that the phase distortion is corrected in advance, maintaining signal integrity while allowing the supply voltage to be reduced for improved efficiency.
Solution Approach 2:
The patent changes the parameters of the supply voltage waveform by adding a DC offset component to the envelope tracking waveform. This parameter modification allows the supply voltage to maintain a minimum level that prevents excessive phase distortion while still enabling efficiency improvements through envelope tracking.
2Loss of energy
If digital signal processing is used to pre-distort I and Q values, then efficiency improves, but device complexity increases
Solution Approach 1:
The patent simplifies the digital signal processing by changing the approach from complex pre-distortion algorithms to a simpler DC offset addition method. This parameter change in the control strategy reduces computational complexity while maintaining the efficiency benefits of envelope tracking.
Solution Approach 2:
The patent extracts the essential function from complex pre-distortion algorithms and retains only the critical DC offset component. This extraction simplifies the digital signal processing requirements while preserving the main efficiency improvement mechanism.
3Loss of energy
If envelope tracking is implemented without DC offset, then efficiency improves, but transmit slot ramp-up and ramp-down problems occur
Solution Approach 1:
The patent changes the waveform parameters by superimposing a DC offset on the envelope tracking signal. This parameter modification ensures that the supply voltage maintains appropriate levels during transmit slot transitions, preventing ramp-up and ramp-down problems while preserving efficiency benefits.
Solution Approach 2:
The patent applies preliminary action by pre-establishing the DC offset level before transmit slot transitions occur. This ensures that the supply voltage is already at the appropriate level to handle upcoming transitions smoothly, preventing instability during ramp-up and ramp-down periods.
Data Source
AI summary
A method and device for improving the efficiency of an envelope tracking transmitter in which a power amplifier for coupling modulated signals in a carrier frequency to an antenna for transmission. The transmitter comprises a power supply for providing a supply voltage to the power amplifier, and a computation means for providing a waveform indicative of the envelope of the modulated signal to the power supply in order to modify the supply voltage. A lower limit is imposed to the waveform so that the supply voltage to the power supply is always greater than a predetermined value. Moreover, when information is transmitted in times slots which are started and ended by ramp periods, a constant signal, based on the root-mean-square value of the waveform, is used to modify the waveform so that the supply voltage to the power amplifier includes a constant voltage level in the ramp periods.