Low-Noise Amplifier Reactive Feedback Without Trifilar Coupling
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Solution Overview
Problem
Low-noise amplifiers face limitations in gain-boosting and impedance-noise matching due to unwanted mutual inductance between transformer windings, particularly in trifilar designs, which also increase fabrication costs with two thick RF metal layers.
Innovation Solution
The use of separate transformers for negative and positive reactive feedback loops, with the second transformer providing positive feedback solely on the input side and the first transformer providing negative feedback via ac coupling without mutual coupling, allowing for one thick RF metal layer fabrication and reducing fabrication costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a trifilar transformer is used to provide both positive and negative feedback loops, then gain is increased, but unwanted mutual inductance between primary and tertiary windings reduces overall gain-boosting and impedance-noise matching
Solution Approach 1:
The patent divides the feedback system into two separate transformers: a first transformer for negative feedback and a second transformer for positive feedback. This segmentation eliminates the unwanted mutual inductance between windings that occurs in trifilar transformers, while still achieving both gain-boosting and impedance control functions
Solution Approach 2:
The patent extracts the positive feedback function from the first transformer and implements it through a second transformer. This separation removes the harmful interaction between windings while preserving the beneficial gain-boosting effect of positive feedback
2Reliability
If trifilar and multi-winding transformer designs are implemented as integrated circuits, then high-Q transformer can be achieved, but two thick RF metal layers are required which increases fabrication cost
Solution Approach 1:
By segmenting the feedback loops into separate transformers, the patent enables implementation with standard single-layer thick metal RF IC fabrication processes, eliminating the need for expensive two-layer processes while maintaining high-Q performance
Solution Approach 2:
The patent uses a simpler, cheaper fabrication approach (single thick metal layer) that achieves the required performance without relying on expensive multi-layer processes, making the solution more economically viable for integrated circuit production
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 enhances gain-boosting capabilities while maintaining well-defined input impedance, achieving higher gain and reducing fabrication costs by eliminating unwanted feedback and allowing for chip-level fabrication with a single thick metal layer.
Implementation Method 1
uses monolithic transformers arranged to create a negative reactive feedback loop across an amplifying element (typically one or more transistors) by way of mutual inductance
Implementation Method 2
The positive reactive loop is provided by the second transformer provided solely on the input side of the amplifying element
Implementation Method 3
The first transformer is coupled to the second transformer (with its intermediate tap point receiving the input to the amplifier, e.g., the RF input signal from an antenna) to form a negative feedback loop
Data Source
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AI summary
An amplifier, comprising: an amplifying element having an input side and an output side; a first transformer on the output side of the amplifying element arranged to mutually couple a fraction of the output current from the amplifying element onto the input side of the amplifying element; a second transformer on the input side of the amplifying element arranged to increase the input voltage on the input side via mutual coupling of its primary and secondary windings; wherein a primary winding of the first transformer is connected to an output of the amplifying element; wherein a secondary winding of the first transformer is ac connected to a secondary winding of the second transformer; and wherein the primary winding of the first transformer is dc blocked from the secondary winding of the second transformer. The negative and the positive reactive feedback loops are not formed from the same trifilar transformer. Therefore, there is no unwanted feedback between the primary and tertiary windings that detracts from the gain and/or impedance-noise matching. The positive reactive loop is provided by the second transformer provided solely on the input side of the amplifying element. The negative reactive feedback loop is provided via the first transformer that provides its feedback to the second transformer without the two transformers being mutually coupled, but with a dc block that maintains the dc isolation across the amplifying element. A significant advantage of this arrangement compared with the trifilar design is that in addition to removing the unwanted coupling between primary and tertiary windings (i.e., selective mutual coupling), the amplifier can be fabricated on chip using one thick RF metal layer fabrication process.