RF Pulse Signal Circuit Using Amplitude Decomposition for Low ACLR
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Solution Overview
Problem
Current RF signal generators in transmitters, particularly in communication devices, fail to sufficiently reduce quantization noise, which leads to inadequate Adjacent Channel Leakage Ratio (ACLR) compliance in standards like W-CDMA, as the noise leaks into adjacent channels and cannot be effectively removed by existing filters.
Innovation Solution
An RF signal generating circuit that includes a polar converter, a signal decomposer generating pulse width control and residual signals, a delta-sigma modulator for delta-sigma modulation of the residual signal, a pulse width modulator for pulse modulation of the phase signal, and a mixer to produce an RF pulse signal, where the signal decomposer ensures the product of the fundamental wave component and residual signal equals the amplitude signal, and a class-D amplifier circuit with multiple switch elements connected to different power supplies to minimize noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional RF signal generator uses a simple modulator without signal decomposition, then the device complexity is reduced, but quantization noise increases and ACLR compliance deteriorates
Solution Approach 1:
The amplitude signal is decomposed into multiple components (fundamental wave component and residual signal) through the signal decomposer. This segmentation allows the delta-sigma modulator to process only the residual signal, thereby reducing quantization noise while maintaining signal fidelity. The decomposition divides the original complex modulation task into manageable parts with different noise characteristics.
Solution Approach 2:
The fundamental wave component is extracted from the amplitude signal before modulation. By removing this dominant component, the remaining residual signal has significantly reduced amplitude and generates much less quantization noise when processed by the delta-sigma modulator. This extraction approach isolates the noise-generating portion of the signal.
2Device complexity
If quantization noise is not sufficiently reduced before filtering, then the signal processing complexity is reduced, but ACLR compliance deteriorates due to noise leaking into adjacent channels
Solution Approach 1:
The signal decomposer and delta-sigma modulator are configured to reduce quantization noise before the signal reaches the filter stage. This preliminary noise reduction action ensures that quantization noise is minimized at the source, preventing it from leaking into adjacent channels. The noise suppression is performed in advance rather than relying solely on post-modulation filtering.
3Loss of energy
If a switching amplifier circuit is used to achieve high power efficiency, then energy consumption is reduced, but the circuit requires precise RF pulse signal generation to maintain waveform integrity
Solution Approach 1:
The signal decomposer uses feedback from the residual signal to adjust the fundamental wave component, ensuring that their product accurately reconstructs the original amplitude signal. This feedback mechanism maintains waveform integrity despite the complex modulation process, ensuring that the RF pulse signal generated for the switching amplifier has the precise amplitude characteristics required for high-efficiency operation.
Data Source
AI summary
An RF signal generating circuit that generates, from a digital signal, an RF pulse signal to be radio-transmitted. It includes a polar converter generating an amplitude signal and a phase signal from the digital signal; a signal decomposer receiving the amplitude signal as an input signal, and generates two signals, a pulse width control signal and a residual signal; a delta sigma modulator subjecting the residual signal to delta-sigma modulation; a pulse width modulator subjecting the phase signal to pulse modulation in accordance with the pulse width control signal, and outputting a pulse phase signal; and a mixer that mixes a signal output from the delta sigma modulator and the pulse phase signal to output the RF pulse signal. The signal decomposer generates the pulse width control and residual signals if a product of a fundamental wave component of the pulse phase and residual signals equals the amplitude signal.