Envelope Tracking RF Amplifier Gain Control Across Signal Bandwidth
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Solution Overview
Problem
In envelope tracking controlled amplifiers, the supply voltage provided by power supplies like DC-to-DC converters decreases with increasing bandwidth of the input signal, leading to deviations from the desired gain trajectory, which can increase Adjacent Channel Leakage Rate (ACLR) and result in suboptimal amplifier performance.
Innovation Solution
A circuit and method that generate a control signal based on the bandwidth of the baseband signal to compensate for the variations in supply voltage, ensuring a constant gain trajectory for the amplifier by adjusting the input voltage to the power supply, thereby maintaining the desired gain trajectory independent of bandwidth changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the supply voltage is adjusted based on instantaneous power demand to enable efficient amplifier operation, then energy efficiency is improved, but the supply voltage becomes dependent on signal characteristics causing gain deviations
Solution Approach 1:
The patent implements feedback by measuring the actual supply voltage at the amplifier and using this measurement to adjust the control signal to the DC-to-DC converter. This closed-loop feedback mechanism compensates for bandwidth-dependent voltage drops, maintaining stable amplifier gain while preserving envelope tracking energy efficiency
Solution Approach 2:
The patent changes the control parameter from a fixed shaping function output to a dynamically adjusted control signal that incorporates actual supply voltage measurements. This parameter adjustment compensates for bandwidth effects and maintains consistent amplifier performance across different operating conditions
2Adaptability or versatility
If the DC-to-DC converter operates with higher bandwidth input signals, then signal processing capability is improved, but the output supply voltage decreases due to gain dependency on bandwidth
Solution Approach 1:
The feedback mechanism measures the actual supply voltage output and uses this information to adjust the DC-to-DC converter's control signal, compensating for the bandwidth-dependent voltage drop and maintaining stable power delivery across different bandwidth conditions
Solution Approach 2:
The system performs preliminary measurement of the supply voltage characteristics and pre-adjusts the control signal to anticipate and compensate for voltage drops before they affect amplifier performance, ensuring stable operation across bandwidth variations
3Reliability
If the amplifier gain is maintained constant over wide input power levels through shaping function, then iso-gain operation is achieved, but the gain trajectory deviates when bandwidth increases
Solution Approach 1:
The feedback loop continuously monitors the supply voltage and adjusts the control signal to the DC-to-DC converter, compensating for bandwidth-induced voltage variations and maintaining the desired iso-gain trajectory independent of signal bandwidth
Solution Approach 2:
The system transitions from a static shaping function to a dynamic control mechanism that adapts the supply voltage in real-time based on actual measurements, enabling the amplifier to maintain consistent gain characteristics across varying bandwidth conditions
Data Source
AI summary
A circuit for generating a radio frequency signal is provided. The circuit includes an amplifier configured to generate a radio frequency signal based on a baseband signal. Further, the circuit includes a power supply configured to generate a variable supply voltage based on a control signal indicating a desired supply voltage, and to supply the variable supply voltage to the amplifier. The circuit further includes an envelope tracking circuit configured to generate the control signal based on a bandwidth of the baseband signal, and to supply the control signal to the power supply.