Multiband Voltage-Controlled Oscillator Without Switched Capacitors
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Solution Overview
Problem
Conventional oscillators face challenges in achieving reliable frequency tuning over a wide band at high frequencies, such as tens of gigahertz, due to steep tuning slopes that increase noise sensitivity and difficulties in accurately controlling small switched capacitors, especially in millimetric wave communications.
Innovation Solution
A controlled oscillator with a tunable capacitor, inductance, and active impedance formed by a cross-connected transistor pair, where a degeneracy is introduced by adjustable resistive impedances between the transistors, allowing for a capacitive component to be tuned, creating multiple frequency ranges with moderate slopes and improved noise immunity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a large swing varactor is used to expand the frequency tuning range, then the oscillator can scan the full required band, but the tuning slope becomes too steep making the oscillator too sensitive to noise
Solution Approach 1:
The frequency tuning range is divided into multiple bands, with each band covered by a dedicated oscillator core tuned to a specific center frequency. This segmentation allows each oscillator to operate with a moderate tuning slope within its specific band, thereby reducing noise sensitivity while collectively covering the full required frequency range through the bank of oscillators.
2Adaptability or versatility
If switched capacitors are used to create multiple tuning bands, then adjacent tuning ranges are created with moderate slopes, but at frequencies of several tens of gigahertz the stray capacitance reduces oscillation frequency and the small capacitor sizes make accurate control difficult
Solution Approach 1:
The patent replaces the mechanical/electrical switching of capacitors with a digital synthesis approach. Each oscillator core is tuned to a specific center frequency determined by its LC tank components, and the overall frequency coverage is achieved by selectively activating different oscillator cores rather than by switching capacitors. This eliminates the stray capacitance issues and small capacitor control problems associated with high-frequency switched capacitor designs.
3Object-affected harmful factors
If the oscillator tuning slope is reduced to improve noise immunity, then the oscillator becomes less sensitive to noise, but the frequency scanning capability across the full required band is compromised
Solution Approach 1:
The frequency spectrum is segmented into multiple bands, with each band handled by a dedicated oscillator core. Each oscillator operates with a moderate tuning slope optimized for its specific center frequency, ensuring good noise immunity within its band. The collective bank of oscillators provides comprehensive frequency scanning capability across the entire required range by switching between different oscillator cores as needed.
Solution Approach 2:
Multiple oscillator cores are designed with similar circuit topologies and components, making them functionally universal. Each core can operate independently at its designated center frequency with optimized noise performance, while the entire bank of oscillators collectively provides the universal frequency coverage capability. This multi-functionality allows the system to achieve both noise immunity and frequency scanning capability.
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
The solution enables accurate and reliable frequency tuning over a wide band at high frequencies, reducing noise sensitivity and improving the (tuning range)/(central frequency) ratio, outperforming existing oscillators by achieving a 20% band coverage with moderate tuning slopes, enhancing noise immunity.
Implementation Method 1
The role of active impedance Za is to produce a negative resistive component at the terminals of energy tank LC tending to compensate the effect of stray resistor Rp so as to maintain oscillation at the resonance frequency of tank LC
Implementation Method 2
The capacitance of varactor C is tunable around a nominal value by a control voltage Vc
Implementation Method 3
means or circuitry for introducing into the crossed pair a degeneracy tunable by a second signal, resulting in the crossed pair producing a capacitive component tunable by the second signal at the terminals of the active impedance
Data Source
AI summary
A controlled oscillator includes, connected in parallel, a capacitor configured to be tuneable based upon a first signal, an inductor, and an active impedance. The active impedance is formed by a pair of cross-coupled transistors connected so as to produce a negative resistive component at the terminals of the active impedance. Circuitry produces a degeneracy tuneable by a second signal in the cross-coupled pair, such that the cross-coupled pair produces a capacitive component tuneable based upon the second signal at the terminals of the active impedance.