IQ Local Oscillator Feedback for Accurate Phase Control
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Solution Overview
Problem
Conventional local oscillators face challenges in generating accurate IQ signals with phase accuracy of less than 0.5% due to element variation in semiconductor integrated circuit devices, particularly at high frequencies like those in the millimeter wave band.
Innovation Solution
A local oscillator design incorporating a multiphase voltage-controlled oscillator (VCO) with a phase locked loop (PLL), multiplier group, phase detector, comparator, and filter, which uses multiple voltage-controlled oscillators in a ring configuration to generate IQ signals with high phase accuracy by controlling phase differences through negative feedback mechanisms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a multiphase voltage-controlled oscillator (VCO) is manufactured using a semiconductor integrated circuit device, then the phase difference between IQ signals is determined by element values, but phase accuracy deteriorates due to element variation within the chip
Solution Approach 1:
The patent introduces a feedback mechanism where a phase detector detects the phase difference between IQ signals and generates a detection result, which is then fed back to control the phase of at least one VCO. This closed-loop feedback system dynamically adjusts the phase to compensate for element variations, achieving phase accuracy of 0.1 degrees or more despite semiconductor manufacturing tolerances
Solution Approach 2:
The system performs self-correction by automatically detecting its own phase error and adjusting its own operation. The phase detector monitors the actual phase difference, and the control mechanism automatically modifies the VCO phases to maintain the desired 90-degree quadrature relationship, enabling the system to self-correct for manufacturing variations
2Speed
If the local source oscillates at twice or four times the desired frequency and uses rising and falling edges, then frequency multiplication is achieved, but implementation becomes difficult at millimeter wave band frequencies
Solution Approach 1:
Instead of multiplying the local oscillator frequency to reach the desired frequency, the patent inverts the approach by using frequency division. The local source oscillates at a lower frequency (one-quarter or one-half of the signal frequency), and frequency division is performed on the signal to achieve the desired frequency relationship, making millimeter wave implementation feasible
3Reliability
If frequency division is used where the local source oscillates at twice or four times the desired frequency, then phase noise characteristics improve, but the local oscillator cannot be implemented at millimeter wave frequencies
Solution Approach 1:
The patent inverts the conventional frequency relationship by making the local oscillator frequency lower than the signal frequency. The local source operates at one-quarter or one-half of the signal frequency, and frequency division is applied to the signal rather than multiplication to the local oscillator, enabling both phase noise improvement and millimeter wave implementation
Data Source
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Figure 3A~3B
AI summary
A local oscillator of the present invention includes: a frequency generator for outputting first and second sinusoidal signals having the same frequency but mutually different phases; a phase detector for outputting either a positive or a negative voltage depending on whether a phase difference between the first and second sinusoidal signals output from the frequency generator is greater than a reference phase difference; and a comparator for outputting a comparison result between a voltage output from the phase detector and a reference voltage, or a comparison result between the voltage output from the phase detector and a voltage obtained by inverting the polarity of the voltage, in which the frequency generator controls the phase of the first sinusoidal signal so that the phase difference approaches the reference phase difference by using the comparison result output from the comparator, enabling generating IQ signals having higher phase accuracy than conventional local oscillators.