Passive Impedance Network in LC Oscillators for Lower Phase Noise
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Solution Overview
Problem
Existing oscillators, particularly LC oscillators, face challenges in reducing phase noise, which affects the performance of electronic systems such as transceivers and clock and data recovery circuits, due to noise sources from active devices and capacitor switching networks.
Innovation Solution
The implementation of a resonant circuit with a passive impedance network that biases active devices in the sustaining amplifier and a switching network to reduce phase noise, using inductors to resonate capacitance and generate high impedance, thereby minimizing thermal noise and switch noise contributions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a sustaining amplifier with active devices is used to drive the resonant circuit, then the oscillator can generate a relatively high frequency output signal, but phase noise increases due to thermal noise from the active devices
Solution Approach 1:
The patent extracts and removes the harmful thermal noise contribution from the sustaining amplifier by using a passive impedance network to block the DC bias path while allowing AC signal passage. This separation enables the amplifier to operate without injecting excessive thermal noise into the resonant circuit, thereby reducing phase noise while maintaining high frequency operation
Solution Approach 2:
The passive impedance network acts as an intermediary element between the sustaining amplifier and the resonant circuit. It mediates the interaction by providing DC bias blocking while maintaining proper operating conditions, thus reducing the direct noise coupling path from the active devices to the resonant circuit
2Adaptability or versatility
If capacitor switching networks are used to tune the resonant frequency, then frequency tunability is achieved, but phase noise increases due to switch noise and parasitic capacitance
Solution Approach 1:
The patent replaces the traditional mechanical capacitor switching network with a passive impedance network approach. Instead of physically switching capacitors that introduce noise and parasitics, the invention uses impedance transformation and DC blocking techniques to achieve frequency tuning while minimizing noise contributions from switching elements
3Reliability
If DC bias is applied to control terminals of switches in the sustaining amplifier, then proper operation of the amplifier is maintained, but thermal noise from the bias path couples into the resonant circuit
Solution Approach 1:
The patent segments the DC bias path from the AC signal path using a passive impedance network. The DC bias is applied through a separate path that does not directly couple to the resonant circuit, while the AC signal path remains intact. This segmentation allows the amplifier to operate reliably with proper DC bias while preventing thermal noise from coupling 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 significantly reduces phase noise by decreasing the conduction angle of the sustaining amplifier and minimizing noise at zero crossing points, while maintaining tunability and reducing parasitic capacitance, thus enhancing the noise performance of oscillators.
Implementation Method 1
The passive impedance network is configured to resonate a capacitance associated with the sustaining amplifier
Implementation Method 2
The one or more explicit passive impedance elements include at least one inductor
Data Source
AI summary
Apparatus and methods are disclosed related to an oscillator that includes a sustaining amplifier. One such apparatus includes a resonant circuit configured to operate at a resonant frequency, a sustaining amplifier, and a passive impedance network. The resonant circuit can have a first terminal and a second terminal. The sustaining amplifier can include at least a first switch configured to drive the first terminal of the resonant circuit in response to an input at a first control terminal of the first switch. The passive impedance network can be configured to pass a bias to the first control terminal, such as a gate of a field effect transistor, of the first switch. The passive impedance network can be electrically coupled to the second terminal of the resonant circuit and can include at least one inductor.