T-Coil Artificial Transmission Line for Compact RF Delay Circuits
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Solution Overview
Problem
The implementation of transmission line structures in radio frequency or microwave monolithic integrated circuits is challenging due to constraints on minimum length, making it difficult to use them when the operating frequency is below about ten gigahertz, as the physical dimensions or circuit area preclude the use of such structures when the operating wavelength approaches a substantial fraction of a centimeter or more.
Innovation Solution
An artificial transmission line structure is formed using lumped or discrete circuit elements to mimic the electrical properties of an actual transmission line, comprising unit cells with t-coil sections including magnetically-coupled inductors, which can provide a linear phase response and constant group delay, allowing for phase shifting and delay line applications with reduced area consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If actual transmission line structures are used in monolithic circuits, then transmission line characteristics can be achieved, but the physical dimensions or circuit area become too large when operating wavelength is substantial fraction of a centimeter or more
Solution Approach 1:
The patent creates an artificial transmission line structure that copies the electrical characteristics of a real transmission line using lumped circuit elements (inductors and capacitors) arranged in unit cells. This allows the circuit to exhibit transmission line behavior without requiring the physical dimensions of an actual transmission line, thus achieving the desired electrical characteristics while dramatically reducing the circuit area.
Solution Approach 2:
The patent transforms the continuous distributed parameters of a real transmission line (inductance per unit length, capacitance per unit length) into discrete lumped parameters through unit cell design. By changing from distributed to lumped parameters and using magnetic coupling between inductors, the structure achieves equivalent electrical characteristics at a much smaller scale appropriate for monolithic integrated circuits.
2Ease of operation
If traditional transmission line structures are implemented, then proper electrical length can be achieved for microwave circuits, but the minimum length constraints make implementation difficult when operating frequency is below about ten gigahertz
Solution Approach 1:
The patent divides the transmission line into discrete unit cells, each containing lumped inductors and capacitors. This segmentation allows the transmission line functionality to be implemented in a modular fashion using small discrete elements that can be easily integrated into monolithic circuits, avoiding the minimum length constraints that plague traditional continuous transmission line implementations at lower frequencies.
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 artificial transmission line structure enables efficient implementation in monolithic circuits by providing a compact solution for phase shifting and delay lines with a linear phase response and extended bandwidth, overcoming the size constraints of traditional transmission line structures.
Implementation Method 1
a first t-coil section defined by a first inductor mutually magnetically coupled and conductively coupled in series with a second inductor
Data Source
AI summary
An electrical circuit can be formed at least in part using lumped or discrete circuit elements to provide an artificial transmission line structure that can mimic the electrical properties of a corresponding actual transmission line structure. Such an artificial transmission line structure can generally consume less area than an actual transmission line structure lacking such lumped or discrete elements. Such an artificial transmission line structure can be formed using two or more “unit cells” such as by cascading such cells as shown and described herein. The present inventors have recognized, among other things, that a unit cell of an artificial transmission line structure can include a t-coil section comprising magnetically-coupled inductors. Such an artificial transmission line structure can be used for applications such as phase shifting or to provide a delay line having a substantially constant group delay, among other applications.