SSB Receiver Calibration for Residual Image Signal Cancellation
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Solution Overview
Problem
Existing SSB receiver calibration methods suffer from high residual image signals and complex hardware, leading to inaccurate phase and amplitude measurements in applications like road tolling, where precise localization is required.
Innovation Solution
A method for calibrating SSB receivers by adjusting phase shift values and measuring phase differences between test signals to minimize residual image signals, using simple and inexpensive hardware components like capacitor and resistor banks with switches for precise phase and amplitude adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If current calibration methods are used to cancel image signals, then image signal cancellation is achieved, but residual misalignments remain due to component ageing or temperature changes, leading to distorted phase and amplitude measurements
Solution Approach 1:
The patent applies preliminary action by performing calibration before actual signal reception to establish accurate phase relationships. The method pre-determines calibration values that compensate for potential misalignments, ensuring that when the receiver operates, the image signal cancellation is already optimized. This preliminary calibration step addresses component ageing and temperature variations by establishing baseline correction values before they cause degradation.
Solution Approach 2:
The patent implements feedback by measuring phase differences between test signals and using these measurements to adjust calibration values. The system continuously monitors the phase relationships and adjusts the calibration parameters accordingly, creating a closed-loop system that maintains accurate image signal cancellation despite environmental changes or component ageing over time.
2Measurement precision
If complex calibration hardware is used to achieve efficient image cancellation, then measurement accuracy improves, but device complexity and cost increase
Solution Approach 1:
The patent replaces complex mechanical or hardware-based calibration systems with a signal processing-based calibration method. Instead of using additional physical components or complex hardware adjustments, the invention uses mathematical calculations and software-based phase measurements to achieve accurate image signal cancellation. This substitution of mechanical/hardware complexity with computational methods reduces device complexity while maintaining or improving measurement precision.
Solution Approach 2:
The patent uses test signals that are copies or representations of actual communication signals to perform calibration. By using simplified test signals with known phase relationships, the system can determine calibration parameters without needing complex hardware. These test signal copies allow the system to measure phase differences and establish calibration values using inexpensive signal generation and measurement techniques rather than complex calibration equipment.
Data Source
Figure 1
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AI summary
The present invention relates to a method for calibrating a single sideband, SSB, receiver (1), the method (M) comprising: a) adjusting a mutual phase shift (ΔΘ) of I- and Q-signals (I, Q) to a first phase shift value (ΔΘ1); b) feeding a first, a second and a third test signal (S1, S2, S3) having a predetermined phase offset (ΔΦ) to an input (2) to obtain respective SSB signals (R1, R2, R3), and measuring a first and a second phase difference (Δϕ12, Δϕ23) therefrom; c) calculating a first phase error (Eϕ,1) on the basis of the first and second phase differences (Δϕ12, Δϕ23); d) repeating steps a) - c) with a second phase shift value (ΔΘ2) to obtain a second phase error (Eϕ,2); and e) calibrating the SSB receiver (1) by using that one of the first and second phase shift values (ΔΘ1, ΔΘ2) that has yielded the smaller one of the first and second phase errors (Eϕ,1, Eϕ,2).