Millimeter-Wave Oscillator Layout to Eliminate Miller Effect
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Solution Overview
Problem
Existing voltage-controlled oscillators (VCOs) face limitations in millimeter wave frequencies due to reduced breakdown voltages, parasitic capacitances, and the Miller effect, which restrict oscillation amplitude, dynamics, and phase noise performance, especially with modern bipolar technologies and CMOS processes.
Innovation Solution
The proposed oscillator design eliminates the Miller effect and dynamics limitations by connecting the collector or drain terminals to the power supply voltage, reducing parasitic capacitances and using inductive elements and capacitive elements to enhance tuning range and phase noise performance, while minimizing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If modern bipolar technologies with miniaturized transistors are used, then integration density is improved, but breakdown voltages are reduced which limits oscillation amplitude and dynamics
Solution Approach 1:
The oscillator is divided into two stages: a first oscillation stage generating the millimeter wave signal and a second amplification stage boosting the signal. This segmentation allows the first stage to operate at minimal amplitude suitable for modern miniaturized transistors, while the second stage provides the necessary signal amplitude, thus resolving the contradiction between small transistor size and sufficient oscillation amplitude.
2Reliability
If varactor elements of minimum size are used, then quality factor and linearity are improved, but parasitic capacitances limit the tuning range
Solution Approach 1:
The patent introduces an inductor in series with the varactor, transforming the tuning mechanism from purely capacitive to a combination of inductive and capacitive elements. This dimensional change in the impedance tuning approach allows achieving wide tuning ranges while maintaining small varactor sizes and high quality factors, as the inductor provides additional tuning degrees of freedom.
3Reliability
If differential circuit configuration is used, then common mode rejection and robustness are improved, but circuit complexity increases
Solution Approach 1:
The differential oscillator is segmented into two independent but symmetrical half-circuits, each implementing a simplified Colpitts oscillator topology. This segmentation maintains the benefits of differential configuration (common mode rejection, robustness) while reducing the complexity of individual circuit blocks, as each half can be designed and analyzed independently.
4Ease of operation
If collector terminals are connected to power supply voltage, then Miller effect and dynamics limitations are eliminated, but output signal collection becomes challenging
Solution Approach 1:
An impedance transformation network (comprising inductors and capacitors) is introduced as an intermediary between the collector terminals and the output signal extraction point. This intermediary allows the collector terminals to remain connected to the power supply voltage (eliminating Miller effect) while providing accessible output signals with appropriate impedance matching for subsequent circuit stages.
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 configuration achieves increased oscillation amplitude, improved phase noise, and expanded tuning range with reduced power consumption, effectively addressing the limitations of existing VCOs in millimeter wave frequencies.
Implementation Method 1
The presence of the inductive element Lb determines a resonance at the frequency and the oscillation is triggered if the negative impedance is able to compensate for the circuit leakages.
Implementation Method 2
The resonator quality factor in the range of millimeter waves is mainly determined by the performance of the components which provide the variable capacitance. These elements are often implemented by means of varactors
Implementation Method 3
The inductance Le offers high impedance between the emitter terminals at the oscillation frequency and further provides a decoupling of the variable capacitors C2 with respect to the parasitic capacitances of the current source Iee
Data Source
AI summary
An oscillator is described, comprising at least one transistor having a first terminal connected to a power supply voltage. The oscillator comprises at least one inductive element connected to a second terminal of the transistor and to a bias voltage and at least one capacitive element coupled between a third terminal of the transistor and ground. The oscillator further comprises means to collect the output signal of the oscillator on the second terminal of the transistor. The oscillator is of the millimeter wave type, i.e., both the inductive element and the capacitive element are sized such that the oscillation frequency is between 30 and 300 gigahertz.