Transformer-Coupled Differential Amplifier for RF Impedance Matching
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Solution Overview
Problem
Transistor amplifiers, particularly common base (CB) and common gate (CG) configurations, face challenges with low input impedance and gain roll-off, leading to impedance matching issues and instability at higher frequencies.
Innovation Solution
The use of a plurality of transformers with primary and secondary windings connected in series, along with differential pairs of transistors, where the secondary windings are connected across the emitter or source terminals, and the collector or drain terminals are connected in parallel, to enhance input impedance and linearity, and a series emitter or gate configuration to match input impedance with the RF source impedance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a common base (CB) configuration is used, then breakdown voltages are larger and gain roll-off is eliminated, but input impedance becomes very low causing impedance matching issues
Solution Approach 1:
A transformer is introduced as an intermediary component between the signal source and the CB amplifier input. The transformer's primary winding connects to the signal source and its secondary winding connects to the amplifier input, providing impedance transformation that matches the low input impedance of the CB configuration to the higher source impedance.
Solution Approach 2:
The input impedance of the CB amplifier is modified by adding a series emitter resistance. This changes the impedance parameter at the input terminal, allowing better matching with the source impedance while maintaining the CB configuration's high breakdown voltage characteristics.
2Ease of operation
If a cascode amplifier is used to increase input impedance, then impedance matching improves, but voltage supply requirements increase
Solution Approach 1:
The input impedance enhancement function is extracted from the cascode configuration and implemented separately using a transformer. This allows the CB amplifier to maintain its simple single-stage structure and low voltage supply requirements while still achieving the desired input impedance matching through the transformer.
3Ease of operation
If feedback techniques are used to increase input impedance, then impedance matching improves, but stability decreases at higher frequencies
Solution Approach 1:
A transformer is used as an passive intermediary component to provide impedance transformation without introducing the active feedback mechanisms that cause stability issues. The transformer achieves impedance matching through its turns ratio while maintaining signal integrity and stability at high 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
This configuration significantly increases the input impedance, improves linearity, and facilitates better impedance matching, reducing output impedance and enhancing the input intercept point, thereby addressing the limitations of conventional CB and CG transistor amplifiers.
Implementation Method 1
a plurality of transformers; wherein each of the plurality of transformers includes a primary and a secondary
Data Source
AI summary
A transistor amplifier includes at least one differential pair of transistors and a plurality of transformers having a primary winding and a tapped secondary winding. The secondary winding is connected across emitters or sources of each transistor pair. The tap of each secondary has a current source. The primary windings of the plurality of transformers are connected in series. The transistor bases or gates are alternating current (AC) grounded. The collector or drain terminal pairs are connected in parallel. The transistor amplifier exhibits improved input impedance and improved linearity.