PLL Oscillator Tuning via Transistor Parasitic Capacitance
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Solution Overview
Problem
Existing phase-locked loops using varactors for frequency tuning suffer from degradation in quality factor and phase noise at higher frequencies due to the inherent signal loss in resonant circuits.
Innovation Solution
A phase-locked loop design utilizing a negative resistance structure with transistors, where the control input signal modulates the parasitic capacitance of the transistors to tune the oscillator frequency, eliminating the need for additional lossy components and reducing frequency-dependent components in the tank network.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If varactors are used for frequency tuning in a voltage controlled oscillator, then fine frequency resolution can be achieved, but the quality factor degrades and phase noise increases at higher frequencies due to signal loss in the resonant circuit
Solution Approach 1:
The patent extracts the tuning function from the resonant circuit by using the negative resistance structure's parasitic capacitance for frequency control, rather than incorporating varactors directly into the resonant tank. This separation removes the lossy varactor component from the high-Q resonant path while preserving the frequency tuning capability through the negative resistance structure that provides both oscillation sustainment and tuning functionality.
Solution Approach 2:
The negative resistance structure is designed to perform multiple functions simultaneously: it provides the necessary negative resistance to sustain oscillations in the voltage controlled oscillator, and its parasitic capacitance serves as the frequency tuning element. This multi-functionality eliminates the need for separate varactor components, reducing overall circuit loss while maintaining fine frequency resolution.
2Adaptability or versatility
If varactors are incorporated into the resonant circuit for tuning, then frequency control is achieved, but the quality factor and phase noise performance deteriorate at mm-wave and THz frequencies
Solution Approach 1:
The tuning capability is extracted from the resonant tank and implemented through the negative resistance structure's inherent parasitic capacitance. This extraction removes the detrimental impact of varactor-induced losses on phase noise performance while preserving the essential frequency tuning functionality needed for PLL operation at mm-wave and THz frequencies.
Solution Approach 2:
The negative resistance structure utilizes its own parasitic capacitance for frequency tuning, eliminating the need for external varactor components. This self-service approach leverages the inherent properties of the active devices already present in the circuit, thereby avoiding additional loss mechanisms that would degrade phase noise performance at high frequencies.
3Adaptability or versatility
If additional tuning components are added to the voltage controlled oscillator, then frequency control is enabled, but the device complexity and number of lossy components increase
Solution Approach 1:
The negative resistance structure is designed to simultaneously provide oscillation sustainment through negative resistance and frequency tuning through its parasitic capacitance. This multi-functional design eliminates the need for separate varactor components, reducing device complexity while maintaining full frequency control capability in the voltage controlled oscillator.
Solution Approach 2:
The tuning function is merged with the negative resistance structure rather than being implemented as a separate component. By combining the oscillation sustainment and frequency tuning functions into a single negative resistance structure, the patent reduces the total number of components and minimizes the introduction of additional lossy elements into the resonant circuit.
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 improves the quality factor and phase noise performance, especially at mm-wave and THz frequencies, by using intrinsic device capacitances for frequency tuning, reducing supply and temperature sensitivity, and enabling fine frequency resolution without introducing additional losses.
Implementation Method 1
the control terminal of at least one of the first and second transistors is biased by the control input signal, such that a parasitic capacitance of said at least one of the first and second transistors can be tuned by the control input signal
Implementation Method 2
a negative resistance structure connected in parallel therewith
Data Source
AI summary
A phase-locked loop comprises a voltage controlled oscillator. The voltage controlled oscillator comprises an inductor and a capacitor, connected in parallel, and also connected in parallel therewith, a negative resistance structure. A first terminal of the negative resistance structure is connected to respective first terminals of the inductor and the capacitor. A second terminal of the negative resistance structure is connected to respective second terminals of the inductor and the capacitor. The negative resistance structure exhibits a tunable capacitance, such that a frequency of an output of the voltage controlled oscillator can be tuned by a control input signal, and the control input signal is generated in the phase-locked loop. The negative resistance structure comprises first and second transistors. There is a first conduction path between the first terminal of the first transistor and the control terminal of the second transistor, and a second conduction path between the control terminal of the first transistor and the first terminal of the second transistor. The control terminal of at least one of the first and second transistors is biased by the control input signal, such that a parasitic capacitance of said at least one of the first and second transistors can be tuned by the control input signal, in order to tune the frequency of the output of the voltage controlled oscillator, and hence the frequency of oscillation of the phase-locked loop.