Envelope-Controlled Transmitter Circuit for PA Distortion Correction
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Solution Overview
Problem
Power amplifiers in wireless communication systems face a trade-off between efficiency and linearity, particularly in 5G systems that need to handle multiple frequency bands, making it challenging to meet error vector magnitude (EVM) and adjacent channel leakage ratio (ACLR) requirements due to AM-AM and AM-PM distortion, which is exacerbated by the high power consumption and complexity of digital predistortion methods.
Innovation Solution
A transmitter circuit architecture that includes a mixer circuit, a power amplifier circuit, a phase-control circuit, and a gain-control circuit to generate phase-adjusted and gain-adjusted signals, counteracting AM-AM and AM-PM distortion by controlling the phase and gain of the local oscillator and power amplifier signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If digital predistortion (DPD) is used to linearize the power amplifier, then linearity (EVM and ACLR performance) is improved, but power consumption and circuit complexity increase significantly
Solution Approach 1:
The patent extracts the essential linearization function from complex digital predistortion and implements it through a simplified analog feedback mechanism. The envelope detector extracts the amplitude envelope, and the feedback loop selectively corrects only the dominant AM-AM and AM-PM distortion components rather than attempting full digital compensation, thereby reducing complexity while maintaining acceptable linearity.
Solution Approach 2:
The invention replaces expensive, power-hungry digital signal processing with simpler, lower-cost analog circuitry. The envelope detector, phase detector, and feedback amplifiers constitute a 'cheaper' alternative to polynomial-based DPD, achieving adequate linearization performance with significantly reduced complexity and power consumption.
2Manufacturing precision
If digital predistortion (DPD) is used to counteract AM-AM and AM-PM distortion, then linearity is improved, but power consumption increases
Solution Approach 1:
The patent substitutes digital signal processing (mechanics of digital computation) with analog circuit operations. The envelope detection, phase comparison, and feedback control are performed using continuous analog signals and circuits, which consume significantly less power than high-speed digital processors required for polynomial-based predistortion.
Solution Approach 2:
The feedback loop continuously monitors the power amplifier output and automatically adjusts the input signal to compensate for distortion. This self-correcting mechanism eliminates the need for complex pre-computation of distortion compensation, allowing the system to maintain linearity with minimal power expenditure through real-time analog adjustment.
3Loss of energy
If the power amplifier operates at high efficiency, then power consumption is reduced, but linearity deteriorates due to AM-AM and AM-PM distortion
Solution Approach 1:
The patent introduces a feedback loop that monitors the power amplifier output and feeds correction signals back to the input. The phase detector compares the phase of the input signal with the feedback signal, and the resulting error signal adjusts the input to compensate for AM-PM distortion. Similarly, the envelope feedback corrects AM-AM distortion, enabling the PA to operate efficiently while maintaining linearity through continuous correction.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution simplifies the circuitry and effectively counteracts distortion, improving the linearity and efficiency of power amplifiers, reducing the need for complex and power-hungry digital predistortion methods, especially for systems handling multiple frequency bands.
Implementation Method 1
a mixer circuit configured to generate a frequency-upconverted signal in response to a phase-adjusted local oscillator (LO) signal and an analog input signal
Implementation Method 2
the phase-control circuit comprises a variable capacitor, the capacitance of which is controlled by the phase-control signal
Data Source
AI summary
A transmitter circuit has a signal input for receiving an analog input signal and a local oscillator (LO) input for receiving an LO signal. A mixer circuit has a first input, a second input, and an output. The second input of the mixer circuit is connected to a signal input of the transmitter circuit. A PA circuit has an input connected to the output of the mixer circuit, and an output. A control circuit generates a phase-control signal and a gain-control signal in response to an envelope of the analog input signal. A phase-control circuit generates a phase-adjusted LO signal in response to the LO signal and the phase-control signal and supplies the phase-adjusted LO signal to the first input of the mixer circuit. A gain-control circuit controls a gain of the transmitter circuit in response to the gain-control signal.