Differential LNA Circuit Without Off-Chip Balun Matching
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Solution Overview
Problem
Existing wireless communication devices face challenges in reducing the number of RFIC package pins and simplifying PCB routing due to the need for differential LNAs, which are sensitive to parasitics and require expensive off-chip balun circuits, while maintaining performance and matching impedance to RF filters.
Innovation Solution
A single-ended-to-differential amplifier design using inductively degenerated transistors with cross-coupled capacitors and inductors, providing well-defined input impedance matching and cancelling noise and nonlinearity, allowing integration on RFIC without external baluns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If differential LNA is used, then receiver performance is improved, but the number of RFIC package pins increases
Solution Approach 1:
The patent inverts the conventional differential LNA architecture by using a single-ended input LNA followed by a differential output stage. This inversion allows the LNA to accept a single-ended input signal (reducing package pins) while still providing differential output signals (maintaining receiver performance). The single-ended input LNA converts the single-ended signal to a differential signal internally, eliminating the need for multiple input package pins.
Solution Approach 2:
The patent segments the LNA function into two distinct stages: a single-ended input LNA stage and a differential output stage. This segmentation allows each stage to be optimized independently - the single-ended stage minimizes package pin requirements while the differential stage ensures robust signal processing. The segmentation resolves the contradiction by separating the input interface requirements from the signal processing requirements.
2Quantity of substance
If single-ended amplifier is used, then package pins are reduced, but sensitivity to parasitics increases
Solution Approach 1:
The patent introduces a differential output stage as an intermediary between the single-ended LNA and the rest of the receiver circuitry. This intermediary stage converts the single-ended signal to a differential signal, providing immunity to common-mode parasitics and disturbances. The differential output stage acts as a mediator that protects the sensitive LNA from parasitic effects while maintaining the benefit of reduced package pins.
Solution Approach 2:
The patent converts the potential harm of single-ended architecture (susceptibility to parasitics) into a benefit by using the single-ended configuration for the LNA input stage (reducing pins) while converting the output to differential form (rejecting parasitics). The harmful effect of single-ended sensitivity is transformed into a beneficial differential output that is immune to common-mode interference.
3Manufacturing precision
If off-chip balun circuit is used, then impedance matching is improved, but cost and complexity increase
Solution Approach 1:
The patent merges the balun (balanced-to-unbalanced transformer) function with the LNA circuit itself, eliminating the need for a separate off-chip balun component. The LNA is designed to directly provide both impedance matching and single-ended to differential conversion in a single integrated circuit. This merging reduces cost, complexity, and component count while maintaining proper impedance matching to RF filters.
Solution Approach 2:
The patent makes the LNA multi-functional by combining several functions into a single circuit: low-noise amplification, single-ended to differential conversion, and impedance matching. This universal LNA design eliminates the need for separate balun and matching network components, reducing overall system complexity and cost while maintaining all necessary functions.
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 amplifier reduces RFIC package pins, simplifies PCB routing, minimizes parasitic effects, and enhances receiver performance by matching impedance and reducing noise and nonlinearity, suitable for multiband operation.
Implementation Method 1
A single-ended-to-differential amplifier design using inductively degenerated transistors with cross-coupled capacitors and inductors
Implementation Method 2
cross-coupled capacitors and inductors
Data Source
AI summary
An amplifier for converting a single-ended input signal to a differential output signal. The amplifier comprises a first transistor, a second transistor, a third transistor and a fourth transistor. The first transistor, configured in common-source or common-emitter mode, receives the single-ended input signal and generates a first part of the differential output signal. The second transistor, also configured in common-source or common-emitter mode, generates a second part of the differential output signal. The third and fourth transistors are capacitively cross-coupled. The amplifier further comprises inductive degeneration such that a source or emitter of the first transistor is connected to a first inductor and a source or emitter of the second transistor is connected to a second inductor.