Calibrating Frequency-Dependent I/Q Mismatch in Direct Up-Conversion Transmitters
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Solution Overview
Problem
Conventional direct-up conversion transmitters suffer from frequency-dependent in-phase (I) and quadrature (Q) mismatches due to component delays in digital-to-analog converters (DACs) and low-pass filters, leading to radio frequency imperfections and reduced signal-to-noise ratio (SNR), despite amplitude and phase calibration.
Innovation Solution
A method and apparatus that utilize test signals with components at specific frequencies to calibrate delay time mismatches by generating adjusted test signals, performing self-mixing operations, and updating calibration parameters based on power measurements at specific frequencies to eliminate frequency-dependent mismatches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If amplitude and phase calibration is performed on I/Q modulator, then amplitude and phase mismatches are corrected, but frequency-dependent mismatches due to component delays remain
Solution Approach 1:
The patent applies preliminary action by performing calibration before actual communication operations. A calibration signal is transmitted through the same signal path, and calibration parameters are computed in advance to compensate for frequency-dependent delays in DACs and LPFs, ensuring accurate I/Q matching across the entire frequency band before real data transmission occurs.
Solution Approach 2:
The patent implements feedback by using the received calibration signal to compute calibration parameters. The calibration signal passes through the complete signal path (DACs, LPFs, mixers), and the received version is compared with the transmitted version to determine delay mismatches. These parameters are then fed back to adjust the I/Q modulator settings, creating a closed-loop calibration system that continuously compensates for frequency-dependent effects.
2Ease of manufacture
If direct up-conversion transmitter architecture is used, then cost, package size and power consumption are reduced, but I/Q mismatch and RF imperfections increase
Solution Approach 1:
The patent applies self-service by enabling the system to calibrate itself without external intervention. The transmitter uses its own internal components (DACs, LPFs, mixers, and signal path) to perform self-calibration by transmitting calibration signals through the complete path and computing correction parameters based on the received signal, eliminating the need for external calibration equipment while compensating for I/Q mismatches.
Solution Approach 2:
The patent implements parameter changes by dynamically adjusting calibration parameters (delay compensation values) based on measured frequency-dependent mismatches. The system computes correction parameters from calibration signals and applies them to modify the signal processing parameters in the I/Q modulator, thereby compensating for RF imperfections while maintaining the simplicity of the direct up-conversion architecture.
3Device complexity
If delay time mismatches in DACs and LPFs are not calibrated, then device complexity is reduced, but frequency-dependent I/Q mismatch increases
Solution Approach 1:
The patent applies universality by making the calibration signal transmission path identical to the normal communication signal path. The same DACs, LPFs, mixers, and signal routing are used for both calibration and actual data transmission, ensuring that the calibration accurately reflects real operating conditions. This multi-functional approach eliminates the need for separate calibration hardware while achieving accurate frequency-dependent I/Q matching.
Data Source
AI summary
A method and apparatus of calibrating I/Q mismatch of a communication circuit is disclosed. The disclosure employs I/Q test signals respectively including different frequency components to calibrate the frequency-dependent I/Q mismatch existing in the communication system.