Calibration Sub-System for Direct Conversion Transmitters
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Solution Overview
Problem
Direct conversion transmitters in telecommunication systems generate undesirable signal components such as local oscillator leakage and sideband image signals due to errors in local oscillator circuits and gain imbalances, which reduce system performance.
Innovation Solution
A calibration sub-system is introduced, comprising a signal generator, receiver, and processor that provides test signals based on modification schemes for in-phase and quadrature signal components to determine optimal parameters, minimizing undesirable signal components by analyzing output power values using functions like Taylor series or polynomial functions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If direct conversion transmitters are used to transmit uplink signals, then signal transmission capability is improved, but local oscillator leakage signals are generated that reduce transmitter performance
Solution Approach 1:
The calibration subsystem performs preliminary calibration actions by generating test signals with known I/Q component characteristics, measuring the actual output signals, and determining calibration parameters that compensate for gain imbalance and phase difference errors before normal operation begins. This preliminary characterization of the transmitter's imperfections enables subsequent correction during actual signal transmission.
Solution Approach 2:
The system changes the parameters of the I and Q signal components (gain values, phase differences) based on calculated calibration parameters. By adjusting these parameters to compensate for measured imbalances and errors, the system reduces local oscillator leakage signals while maintaining the signal transmission capability of the direct conversion transmitter.
2Productivity
If direct conversion transmitters are used to transmit uplink signals, then signal transmission capability is improved, but sideband image signals are generated that reduce transmitter performance
Solution Approach 1:
The calibration subsystem performs preliminary measurements using test signals to characterize gain imbalance between I and Q components and quadrature-mixing phase differences. By establishing these characteristics beforehand, the system can apply appropriate calibration parameters to minimize sideband image generation during normal uplink signal transmission.
Solution Approach 2:
The system adjusts the gain parameters and phase parameters of the I and Q signal components based on calibration results. These parameter changes compensate for gain imbalance and phase errors that cause sideband image signals, thereby reducing their power while preserving the main signal transmission function.
3Reliability
If calibration sub-system is introduced to reduce undesirable signal components, then transmitter performance is improved, but device complexity increases
Solution Approach 1:
The calibration subsystem uses the existing transmitter and receiver components for dual purposes: normal signal transmission/reception and calibration measurements. The signal generator can produce both data signals and test signals, and the receiver processes both types of signals. This multi-functionality reduces the need for entirely separate calibration hardware, thereby limiting the increase in device complexity.
Solution Approach 2:
The calibration subsystem is self-contained within the transmitter unit, using its own components (signal generator, receiver, processor) to perform calibration without requiring external specialized equipment. The system calibrates itself by generating test signals, measuring its own output, and computing calibration parameters internally, which minimizes additional external hardware complexity.
Data Source
AI summary
A calibration sub-system for calibrating a unit of a distributed antenna system is provided. The calibration sub-system includes a signal generator, a receiver, and a processor. The signal generator provides test signals to a communication path that are generated based on modification schemes for an in-phase signal component (“I component”) or a quadrature signal component (“Q component”). The receiver receives output signals generated from test signals. The processor determines output power values for an undesirable signal component of the output signals. Each output power value is a Taylor series function or a polynomial function of a respective modification scheme for the I or Q component of the respective test signal. The processor determines an optimal modification scheme for the I or Q component that minimizes an output power of the undesirable signal component. An output value of the function is minimized by having the optimal modification scheme as an input.