Quadrature Oscillator Startup Control for Stable 90° Phase Lock
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Solution Overview
Problem
Existing quadrature voltage controlled oscillators (QVCOs) face challenges in reliably generating quadrature signals with a fixed 90-degree phase difference, as they often exhibit uncertainty in phase shift and require additional circuitry or modifications that degrade performance, especially at high frequencies.
Innovation Solution
An oscillator circuit with two controllable frequency oscillation circuits and a controller that initially sets their frequencies unequal and then equal, allowing selection of the oscillation mode and resonant frequency, thereby ensuring reliable quadrature signal generation and increased tuning range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If phase shift is introduced in the coupling between oscillator cores to make one mode dominant, then the QVCO can operate in a fixed mode stably, but extra circuitry is added and phase noise is degraded
Solution Approach 1:
The patent applies preliminary action by pre-setting unequal initial frequencies for the two oscillation circuits before quadrature operation begins. This frequency difference acts as a preliminary measure to force the system into a single dominant oscillation mode, eliminating the need for additional phase-shifting circuitry while maintaining mode stability.
Solution Approach 2:
The patent changes the frequency parameter of the oscillation circuits by maintaining a controlled frequency difference between the first and second oscillation circuits. This parameter change forces the system to operate in a specific mode without requiring additional circuit modifications, thus improving reliability while avoiding increased complexity.
2Reliability
If phase shift is introduced in the coupling between oscillator cores, then mode dominance is achieved, but phase noise performance is degraded
Solution Approach 1:
The patent uses preliminary action by establishing unequal initial frequencies before oscillation begins. This pre-conditioning forces mode dominance without introducing additional coupling circuitry that would generate phase noise, thereby maintaining both stability and spectral purity.
Solution Approach 2:
The patent uses two separate oscillation circuits that are essentially copies of each other but operated at different initial frequencies. This approach avoids the need for complex coupled oscillator designs with phase-shifting elements, reducing phase noise while maintaining mode stability.
3Reliability
If capacitive source degeneration is used to introduce phase shift, then mode selection is achieved, but implementation at high frequencies above 30 GHz becomes difficult
Solution Approach 1:
The patent changes the operating frequency parameter by maintaining a frequency difference between the two oscillation circuits rather than relying on capacitive degeneration. This approach is frequency-agnostic and works effectively at high frequencies above 30 GHz where capacitive methods become impractical.
Solution Approach 2:
The patent extracts the phase shift mechanism from the coupling circuitry and replaces it with independent frequency control of the two oscillation circuits. This removes the frequency-limiting capacitive degeneration approach and enables high-frequency operation.
4Ease of operation
If tuning voltage is adjusted to start QVCO in different states, then oscillation mode selection is attempted, but the QVCO always starts in the same mode for all voltage levels
Solution Approach 1:
The patent changes the frequency parameter of the oscillation circuits by applying different initial frequencies rather than relying on tuning voltage adjustments. This ensures reliable mode selection independent of voltage level, overcoming the limitation where QVCO always starts in the same mode regardless of voltage.
Data Source
AI summary
An oscillator circuit (10) for generating quadrature-related first and second oscillation signals having equal frequencies comprises a first oscillation circuit (VCO_I) configured to generate the first oscillation signal having a first controllable frequency, a second oscillation circuit (VCO_Q) configured to generate the second oscillation signal having a second controllable frequency; and a controller (100) configured to enable and disable oscillation of the first and second oscillation circuits (VCO_I, VCO_Q) and to control the first and second controllable frequencies, such that when the oscillation is enabled, the first and second controllable frequencies are controlled to be initially unequal and then to become equal.