Complex Delta-Sigma Modulator for Constant-Envelope PA Transmission
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Solution Overview
Problem
Current delta sigma modulator (DSM) based transmitters suffer from low coding efficiency, significant quantization noise, and degraded signal-to-noise and distortion ratio (SNDR) due to high peak-to-average-power-ratios (PAPRs), leading to inefficient power amplification and limited signal bandwidth.
Innovation Solution
A complex delta-sigma modulator unit with a complex polar quantizer is employed to process complex digital input signals, converting them into a constant envelope signal, and an adjacent channel power ratio (ACPR) enhancement unit is used to reduce noise, allowing the power amplifier to operate at saturation with improved efficiency and linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a two-level DSM unit is used to generate constant-envelope signal, then power amplifier efficiency is improved, but coding efficiency is critically low
Solution Approach 1:
The invention segments the quantization process into multiple levels (three-level polar DSM) rather than using a simple two-level quantizer. This segmentation allows the signal to maintain constant envelope properties while improving coding efficiency by better representing the input signal dynamics across multiple quantization levels.
Solution Approach 2:
The invention changes the quantization parameter structure from binary (two-level) to polar (three-level with positive, zero, negative states). This parameter change enables the modulator to achieve both constant envelope output and improved coding efficiency by utilizing the additional quantization state to better match the signal characteristics.
2Reliability
If PA works at higher power back-off to prevent distortion, then linearity is improved, but power efficiency deteriorates
Solution Approach 1:
The DSM unit performs preliminary quantization and envelope constantization before the signal reaches the power amplifier. By pre-shaping the signal envelope to be constant, the PA can operate at saturation without introducing distortion, eliminating the need for power back-off and thereby maintaining high efficiency while ensuring linearity.
Solution Approach 2:
The invention implements a feedback loop where the quantized output is fed back through the quantizer to refine the quantization decision. This feedback mechanism ensures that the constant envelope signal accurately represents the input while allowing the PA to operate efficiently at saturation without distortion.
3Measurement precision
If quantization noise is reduced to improve SNDR, then signal quality is improved, but signal bandwidth is limited
Solution Approach 1:
The invention moves from a single-dimensional (real-valued) quantization approach to a complex two-dimensional approach by processing both in-phase and quadrature components simultaneously. This dimensional change allows the system to achieve better noise performance through complex signal processing while preserving the full signal bandwidth through parallel I/Q path processing.
Data Source
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AI summary
Apparatuses and methods for power amplification and signal transmission using complex delta-sigma modulation are disclosed. In one embodiment, a complex delta sigma modulator unit comprising a complex polar quantizer within an integrator loop is disclosed. The complex polar quantizer quantizes the envelope of a complex integrated signal and produces a complex quantized output signal of substantially constant envelope. The complex quantized output signal is used in deriving a complex feedback signal within the integrator loop of the complex DSM. The complex quantized output signal may be used in driving a power amplifier substantially at saturation. In some embodiments, an adjacent channel power ratio (ACPR) enhancement technique is used to reduce the quantization noise in the complex quantized output signal.