Transformer-Coupled Mixer Circuit for Low-LO-Power Linearity
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Solution Overview
Problem
Existing mixer circuits, such as square law, single balanced, and double balanced mixers, face challenges with high LO power requirements, poor linearity, and high noise figures, which affect their conversion gain and efficiency in radio transceivers and radar systems.
Innovation Solution
A mixer circuit design incorporating a bipolar/FET transistor with inductive transformer coupling between the base/gate and emitter/source ports, enhancing linearity, conversion gain, and reducing noise figure by increasing the amplitude of voltage differences between input ports, and optionally using a second transistor with similar inductive coupling for improved performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a square law mixer is used, then linearity performance is improved, but LO power input requirement increases and noise figure increases and conversion gain decreases
Solution Approach 1:
The patent introduces a transformer as an intermediary component between the LO input and the mixer core. This transformer provides inductive coupling that enhances the LO signal swing at the transistor terminals, effectively reducing the required LO power input while maintaining the desired mixing performance and linearity characteristics.
Solution Approach 2:
The patent modifies the operating parameters of the mixer by using a transformer with specific turns ratios to transform the LO signal. This parameter transformation allows the mixer to operate with lower LO power input while achieving the same or better linearity performance, effectively changing the power consumption characteristic of the system.
2Manufacturing precision
If a square law mixer is used, then linearity performance is improved, but noise figure increases and conversion gain decreases
Solution Approach 1:
The transformer acts as an intermediary that improves the noise figure by providing better impedance matching and signal transformation. The inductive coupling enhances the LO signal swing without directly coupling noise, thereby reducing the noise figure while maintaining linearity performance.
3Power
If a single balanced mixer is used, then conversion gain is improved, but linearity performance deteriorates
Solution Approach 1:
The transformer serves as an intermediary that simultaneously improves both conversion gain and linearity. By providing inductive coupling and enhanced LO signal swing, the transformer allows the single balanced mixer to achieve better conversion gain while the improved signal symmetry and balance provided by the transformer also enhance linearity performance.
4Manufacturing precision
If transformer coupling is added to improve linearity and conversion gain, then device complexity increases
Solution Approach 1:
The transformer is designed to perform multiple functions simultaneously: it provides inductive coupling for LO signal delivery, transforms impedance for optimal matching, enhances LO signal swing at the mixer terminals, and improves signal symmetry. This multi-functionality reduces the need for additional separate components, thereby limiting the increase in device complexity while achieving improved linearity and conversion gain.
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 proposed mixer circuit achieves lower LO power consumption, improved linearity, and increased conversion gain while reducing noise figure, making it suitable for various mixer types, including square law, single balanced, and double balanced designs.
Implementation Method 1
a transformer which connects the base/gate and emitter/source of the first mixer component inductively to each other
Data Source
Figure 1a~1b
Figure 2~3
Figure 4
AI summary
The invention discloses a mixer circuit (10, 20, 30, 410, 60) comprising a first mixer component (11, 21) with a first (13, 23) and a second (12, 22) input port for a first and a second input signal respectively and an output port (14, 24) for outputting a mixed signal. According to the invention, the mixer circuit (10, 20, 30, 410, 60) also comprises a transformer (15) which connects the first (13, 23) and second (12, 22) input ports of the mixer component (11, 21) inductively via an inverting coupling. In one embodiment, the mixer circuit (30, 410, 60) also comprises inputs for DC-bias of one (13) of the input ports and of the output port (14), as well as an impedance (31) as a filter at the output port.