Digital Gain Control for Cartesian Loop Transmitters
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Solution Overview
Problem
Current Cartesian loop gain control devices in radiocommunication systems face challenges with high current consumption and large silicon area, which are incompatible with the trends towards reduced footprint and integration in mobile equipment, especially with the increase in bit rates and non-constant envelope modulations.
Innovation Solution
A digital processing circuit is used to receive baseband and Cartesian feedback signals, with a gain control stage modifying the gain applied to the baseband input signals, linked to an analogue processing circuit through an analogue/digital and digital/analogue conversion stage, allowing for low consumption and reduced silicon area while maintaining the required gain dynamic range and precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional analogue gain control stages are used to achieve 75 dB dynamic range with 1 dB precision, then the required gain control precision and dynamic range are achieved, but current consumption increases and silicon area footprint increases
Solution Approach 1:
The patent replaces conventional analogue voltage-controlled amplification stages with a digital signal processing approach. A Cartesian loop device processes baseband signals digitally, using complex arithmetic operations (multiplication by exponential terms) to provide gain control. This substitution of digital processing for analogue amplification significantly reduces current consumption while maintaining the required 75 dB dynamic range and 1 dB precision through computational methods rather than physical amplification stages.
2Measurement precision
If conventional analogue gain control stages are used to achieve 75 dB dynamic range with 1 dB precision, then the required gain control precision and dynamic range are achieved, but the silicon area footprint increases
Solution Approach 1:
The patent replaces multiple analogue amplification stages with a compact digital signal processing implementation. The Cartesian loop device uses digital multipliers and complex exponential calculations to achieve gain control, requiring far less silicon area than the cascade of analogue VGA stages needed to achieve the same 75 dB dynamic range with 1 dB resolution. The digital approach consolidates functionality into a smaller footprint suitable for mobile equipment.
3Use of energy by moving object
If digital processing is used to reduce consumption and footprint, then current consumption decreases and silicon area decreases, but maintaining the required gain dynamic range and precision becomes challenging
Solution Approach 1:
The patent implements a Cartesian loop feedback mechanism where the processed baseband signals are combined with feedback signals in a summing junction. This feedback structure enables automatic gain control and linearization, ensuring that the digital processing maintains the required precision and dynamic range. The feedback loop continuously adjusts the processing to compensate for any deviations, guaranteeing accurate gain control despite the reduced hardware footprint.
Solution Approach 2:
The patent uses parameter changes in the form of complex exponential terms (e^(jφ)) to control gain dynamically. By varying the phase parameter φ in the digital multiplication operation, the system achieves continuous gain adjustment across the full 75 dB range with 1 dB precision. This parameter-based control method allows precise gain manipulation without requiring physical amplification stages, maintaining accuracy while reducing power consumption and area.
Data Source
AI summary
A device includes a digital circuit for receiving input signals and Cartesian feedback signals includes a stage for combining the input signals and the feedback signals to generate error signals. The digital circuit is linked via a conversion stage to an analogue circuit suitable for receiving the error signals, and which includes a stage for generating an output signal from the error signals and a stage for generating the feedback signals from the output signal. The digital circuit also includes at least one gain control stage before the combination stage for modifying the gain applied to the input signals.