Coplanar Transformer with Bypass Capacitor for High-Frequency Coupling
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Solution Overview
Problem
Conventional coplanar transformers used in wireless communication devices suffer from low quality (Q) factors and low coupling coefficients (K) for millimeter-wave applications, as well as lower resonance frequencies in advanced technology nodes, necessitating improved transformer designs.
Innovation Solution
The design incorporates a coplanar symmetric transformer with a 1:1 turn ratio, featuring primary and secondary windings on the same metal layer with capacitive coupling between them, allowing for tunable mutual inductance and coupling coefficient, achieved through metal-insulator-metal (MIM) or metal-oxide-semiconductor (MOS) capacitors, which enhance the transformer's performance without increasing area or altering impedance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If conventional coplanar transformers are used to reduce size and resistance, then the transformer occupies less area and has lower resistance, but the quality factor (Q) and coupling coefficient (K) are low
Solution Approach 1:
The patent introduces an intermediary capacitor connected to the center tap of the secondary winding to mediate the coupling between primary and secondary windings. This capacitor acts as a mediator that enhances the magnetic coupling effect without requiring the windings to be physically closer, thereby improving the coupling coefficient while maintaining the compact coplanar structure.
Solution Approach 2:
The patent changes the electrical parameters of the transformer by introducing capacitive elements and adjusting the number of turns in the windings. By modifying the capacitance value and winding turn ratios, the coupling coefficient and quality factor are improved without fundamentally changing the coplanar layout, thus resolving the contradiction between compact size and high coupling.
2Productivity
If transformers are designed for advanced technology nodes (90nm, 65nm, or smaller), then integration density is improved, but the resonance frequency (Fsr) decreases
Solution Approach 1:
The capacitor connected to the center tap serves as an intermediary that compensates for the reduced resonance frequency in advanced technology nodes. By adjusting the capacitance value, the resonant frequency of the transformer can be tuned to higher values, counteracting the natural frequency reduction that occurs with scaled-down dimensions in advanced CMOS processes.
Solution Approach 2:
The patent introduces dynamic tuning capability through the capacitor, allowing the transformer's resonant frequency to be adjusted. This dynamic parameter adjustment enables the transformer to maintain high resonance frequency performance even in advanced technology nodes where fixed-geometry transformers would naturally exhibit lower resonant frequencies.
3Power
If the number of turns in windings is increased to improve voltage ratio, then the voltage transformation capability is improved, but the area and resistance increase
Solution Approach 1:
The patent merges the primary and secondary windings into a single coplanar layer, allowing them to be interleaved and share the same physical space. This merging approach enables high voltage transformation ratios to be achieved without proportionally increasing the total area, as both windings occupy overlapping regions rather than adjacent regions.
Solution Approach 2:
The patent transitions from traditional three-dimensional stacked windings to a two-dimensional coplanar configuration. By utilizing the planar dimension more efficiently with interleaved windings, the voltage transformation capability is maintained or improved while reducing the vertical height and overall footprint of the transformer structure.
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 significantly improves the coupling coefficient (k) to values above 0.78 up to 80 GHz, achieving higher resonance frequencies and maintaining low loss, addressing the limitations of conventional transformers in advanced technology nodes.
Implementation Method 1
capacitive coupling between them, allowing for tunable mutual inductance and coupling coefficient, achieved through metal-insulator-metal (MIM) or metal-oxide-semiconductor (MOS) capacitors
Implementation Method 2
A varying current in the first or primary winding creates a varying magnetic field through the secondary winding. This varying magnetic field induces a varying electromotive force (EMF) or 'voltage' in the secondary winding. This effect is called mutual induction.
Data Source
AI summary
An electronic device comprises first, second and third inductors connected in series and formed in a metal layer over a semiconductor substrate. The first and second inductors have a mutual inductance with each other. The second and third inductors having a mutual inductance with each other. A first capacitor has a first electrode connected to a first node. The first node is conductively coupled between the first and second inductors. A second capacitor has a second electrode connected to a second node. The second node is conductively coupled between the second and third inductors.