Clock-Harmonic Calibration Signal Generation for VLIF IQ Balancing
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Solution Overview
Problem
Very low intermediate frequency (VLIF) receivers require stringent IQ path balancing, which existing calibration methods fail to achieve efficiently due to the high cost of dedicated hardware and slow convergence of adaptive algorithms, especially for enhanced GPRS standards.
Innovation Solution
A calibration signal generator that re-uses existing receiver components to generate test tones using harmonics of a clock source, reducing silicon area and enabling calibration over a large frequency range without the need for additional dedicated test tone synthesizers or external clock sources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If dedicated hardware systems are used for offline calibration, then calibration accuracy is improved, but device cost and complexity increase significantly
Solution Approach 1:
The patent makes existing receiver components (RF front-end, mixer, ADC, clock source) perform dual functions: normal signal reception and calibration signal generation. The clock source generates both operational clock signals and calibration test tones by utilizing harmonic frequencies, eliminating the need for dedicated calibration hardware.
Solution Approach 2:
The receiver performs its own calibration using internally available resources. The system uses its existing clock source to generate calibration signals and its own RF front-end to process these signals, making the calibration process self-contained without requiring external test equipment or additional dedicated hardware.
2Adaptability or versatility
If three different frequency sources are used for calibration, then calibration capability is improved, but silicon area and device cost increase
Solution Approach 1:
A single clock source is designed to fulfill multiple frequency requirements by generating fundamental frequencies and their harmonics. The same clock source provides frequencies for RF operation, LO generation, and calibration signals across different frequency bands, replacing what would traditionally require three separate frequency sources.
Solution Approach 2:
The system utilizes harmonic frequencies (multiples of the fundamental clock frequency) to generate different calibration signal frequencies. By changing which harmonic is selected (2nd harmonic, 3rd harmonic, etc.), the system can generate calibration signals at different frequencies without adding hardware, effectively changing the frequency parameter through mathematical relationships.
3Adaptability or versatility
If adaptive algorithms are used for online calibration, then calibration flexibility is improved, but convergence speed becomes insufficient for enhanced GPRS standards
Solution Approach 1:
The system performs calibration offline using deterministic test tones generated from clock harmonics before normal operation begins. This preliminary calibration establishes accurate balancing parameters in advance, eliminating the need for slow adaptive algorithms during time-critical operations like enhanced GPRS data transmission.
Solution Approach 2:
The calibration process is performed periodically during manufacturing or initialization phases using precise periodic test signals. These deterministic periodic calibration signals allow for rapid measurement and adjustment, contrasting with the continuous iterative nature of adaptive algorithms that require many iterations to converge.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for efficient offline calibration of VLIF receivers, reducing the need for regular re-calibration and minimizing silicon area, while maintaining high performance across various frequency bands.
Implementation Method 1
a squaring amplifier to produce a first calibration signal, of frequency fRX
Implementation Method 2
a synthesizer to generate a second calibration signal, of frequency fC=fRX+/−f0... by mixing the clocking signal with a signal from the synthesizer
Data Source
AI summary
A calibration signal generator for use in a balancing circuit calibration device in a radio receiver, the calibration signal generator comprising: a means of amplifying a clocking signal from a clocking signal generator to provide a first calibration signal; a means of generating a second calibration signal from the clocking signal, the first and second calibration signals being transmissible to a one or more mixing circuits in the balancing circuit calibration device; and a means synchronizing the operation of other circuit elements in the balancing circuit calibration device with the clocking signal; characterized in that the clocking signal generator is present in the radio receiver and used therein for other functions.