Transmission Line Transformer Layout for RF Impedance Matching

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Solution Overview

Problem

Conventional RF power amplifiers with transmission line transformers face impedance mismatching issues due to parasitic inductance at the bonding pad, leading to increased circuit size and reduced efficiency, especially when coupling the output electrode of a power transistor with a transmission line transformer as an impedance matching circuit.

Innovation Solution

The RF amplifying device incorporates a transmission line transformer with a main line and a secondary line, where the output electrode of the power transistor is coupled to one end of the main line, and the secondary line is connected to an AC grounding node, with coupling members electrically joined to a joint formed in the energy coupling part, reducing parasitic inductance and maintaining impedance matching by inductive-capacitive coupling.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If conventional transformers with magnetic flux coupling are used for impedance matching, then impedance conversion can be achieved, but the circuit size becomes larger and frequency band is limited

Engineering Contradiction:

Improvefrequency bandVSAvoidcircuit size

Core Design Contradiction:

Adaptability or versatilityVSArea of stationary object

Solution Approach 1:

The patent replaces conventional magnetic flux coupling transformers with a transmission line transformer that uses electromagnetic wave propagation in transmission lines for coupling. This substitution eliminates the need for magnetic cores and windings, enabling broadband operation and compact integration on PCBs or IC substrates while maintaining impedance matching functionality.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Adaptability or versatility

If transmission line transformer is used for broadband impedance matching, then circuit size is reduced, but parasitic inductance at bonding pad causes impedance mismatching

Engineering Contradiction:

Improvebroadband performanceVSAvoidimpedance matching condition

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent extracts the bonding pad joint from the energy coupling region of the transmission line transformer. By positioning the bonding pad joint outside the critical coupling area between primary and secondary transmission lines, the parasitic inductance does not interfere with the impedance matching function, allowing broadband performance to be maintained while ensuring reliable impedance matching.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent introduces a dedicated joint structure that serves as an intermediary connection point, separating the bonding pad connection from the transmission line coupling region. This intermediary structure allows electrical connection while isolating the parasitic inductance from the impedance matching path, thereby maintaining matching conditions across broad frequency bands.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Power

If large current-carrying spiral coils or choke inductance are used to handle high current, then current capacity is sufficient, but circuit size increases

Engineering Contradiction:

Improvecurrent carrying capacityVSAvoidcircuit size

Core Design Contradiction:

PowerVSArea of stationary object

Solution Approach 1:

The patent replaces traditional spiral coils and choke inductors with transmission line structures that inherently handle high currents through distributed capacitance and inductance along the transmission line. This allows high power handling capability to be achieved without requiring large discrete inductor components, thus maintaining compact circuit size while providing sufficient current carrying capacity.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 allows for effective impedance matching and reduced parasitic inductance, enabling efficient transmission power to a 50-Ω antenna without the need for large current-carrying spiral coils or choke inductance, thus maintaining a compact circuit size and high efficiency.

Implementation Method 1

coupling energy is transmitted from the secondary line to the main line at an energy coupling part where the main line of the transmission line transformer is in close proximity of, and opposite to the secondary line

Methodology Applied

Scientific EffectInductive-capacitive coupling: Electromagnetic Induction

Data Source

PatentUS7825731B2RF amplifying device

Publication Date: 2010.11.02 RENESAS ELECTRONICS CORP

AI summary

An RF amplifying device includes a transmission line transformer coupled to an output electrode of a power transistor for generating transmission power to be fed to an antenna. The transmission power from the output electrode of the power transistor is fed to one end of a main line of the transmission line transformer, and one end of a secondary line of the transmission line transformer is coupled to an AC grounding node. The other end of the secondary line is coupled to the one end of the main line, thereby generating the transmission power. Coupling energy is transmitted from the secondary line to the main line. Coupling members electrically coupled to the output electrode of the power transistor are electrically coupled to a joint formed in either the main line, or the secondary line, at part of the energy coupling part.