Switched VCO Circuit Using a Tapped Inductor for Low-Noise RF
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Solution Overview
Problem
Designing voltage-controlled oscillators (VCOs) that meet noise and power requirements for small-sized, low-cost, and high-frequency products is challenging, especially as RF frequencies increase and supply voltages decrease, leading to decreased inductor size and quality factor, which increases thermal noise.
Innovation Solution
The oscillator circuit employs a tapped inductor with four terminals, allowing operation in inductive feedback or negative resistance modes through switching, and includes amplifiers with specific transistor configurations to manage noise and power consumption, featuring a differential LC tank with a capacitive element and inductive element for improved performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the inductor size is decreased to compensate for decreased supply voltage and increase frequency, then the frequency and voltage requirements are met, but the quality factor decreases and thermal noise increases
Solution Approach 1:
The patent implements dynamic switching between two amplifier configurations (cross-coupled amplifier for negative resistance mode and inductive feedback amplifier for high Q mode) based on operating conditions. This allows the circuit to adaptively optimize performance by selecting the appropriate mode for the current frequency and voltage requirements, resolving the contradiction between high frequency operation and quality factor maintenance.
Solution Approach 2:
The patent changes the operational parameters of the amplifier by switching between different configuration modes. In negative resistance mode, the cross-coupled amplifier provides frequency multiplication capability, while in inductive feedback mode, the amplifier operates with higher quality factor characteristics. This parameter switching allows the system to meet different frequency and quality factor requirements dynamically.
2Speed
If the inductor size is decreased to increase frequency, then the frequency requirement is met, but thermal noise increases
Solution Approach 1:
The circuit dynamically switches between operating modes to minimize thermal noise at different frequencies. At lower frequencies where high Q is beneficial, the inductive feedback mode is selected. At higher frequencies where frequency multiplication is needed, the cross-coupled mode is used. This dynamic adaptation reduces overall thermal noise by optimizing the operating point for each frequency range.
3Device complexity
If a single amplifier configuration is used, then the device complexity is low, but the ability to meet different noise and power requirements in various scenarios is limited
Solution Approach 1:
The patent implements a universal amplifier structure that can perform multiple functions through configuration switching. The same physical amplifier circuit can operate in cross-coupled mode for negative resistance and frequency multiplication, or in inductive feedback mode for high quality factor oscillation. This multi-functionality allows a single device to meet diverse noise and power requirements across different application scenarios without requiring separate dedicated circuits for each function.
Data Source
AI summary
An oscillator circuit is provided, which relates to the field of electronic technologies, to improve performance of an oscillator. The oscillator circuit includes: a first amplifier (Am1) and a second amplifier (Am2), where the first amplifier (Am1) and the second amplifier (Am2) are switchable, and the oscillator circuit is operable in an inductive feedback mode or a negative resistance mode through switching. The oscillator circuit further includes a capacitive element and an inductive element, where the inductive element includes a tapped inductor that includes four terminals (V1, V2, V3, and V4), two of the four terminals are coupled to differential inputs of the first amplifier (Am1) and differential outputs of the second amplifier (Am2), and the other two terminals are coupled to differential outputs of the first amplifier (Am1).