Differential Inductor LNA Balun for Low-Noise RF Signal Balance
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Solution Overview
Problem
Current electronic signal amplifiers in communication systems face challenges in efficiently converting single-ended RF signals to differential signals with low noise and well-balanced outputs, especially across multiple frequency bands, due to difficulties in designing transformers and differential inductors with low signal loss and balanced outputs, which affects noise figure and chip area utilization.
Innovation Solution
A low-noise amplifier (LNA) with a differential inductor configuration, where a center tap is connected to signal ground, and the single-ended input signal is provided to an end tap of the inductor, producing a differential signal that is further processed by a capacitive cross-coupling common-gate LNA to reduce common-mode content and improve signal balance, allowing for efficient amplification and impedance matching across a wide frequency band.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If on-chip transformers or differential inductors are used as baluns to perform single-ended-to-differential conversion, then signal conversion is achieved, but signal loss increases and output balance deteriorates
Solution Approach 1:
The patent combines the balun function and LNA function into a single integrated circuit. The differential inductor serves dual purposes: as a balun for single-ended-to-differential conversion and as part of the LNA amplification circuit. This merging eliminates the need for separate transformer components, reducing signal loss and improving output balance while maintaining compact chip area.
Solution Approach 2:
The differential inductor is designed to perform multiple functions simultaneously: it acts as the balun for signal conversion, provides impedance matching, and serves as the load inductor for the LNA. This multi-functionality reduces the number of discrete components needed, thereby reducing overall signal loss and improving circuit reliability.
2Area of stationary object
If separate balun and LNA circuits are used, then signal conversion and amplification are achieved, but chip area increases
Solution Approach 1:
The patent integrates the balun and LNA into a single on-chip circuit. The differential inductor is shared between the balun conversion function and the LNA amplification function. This integration significantly reduces chip area while maintaining low noise figure by minimizing the number of discrete components and interconnections.
3Reliability
If conventional differential inductor configuration is used, then signal amplification is achieved, but common-mode content increases
Solution Approach 1:
The patent employs asymmetric capacitor coupling in the LNA circuit. The capacitors are strategically placed to create asymmetric signal paths that selectively reject common-mode signals while preserving differential-mode signals. This asymmetric configuration improves common-mode rejection ratio without significantly increasing noise figure.
Solution Approach 2:
The patent introduces capacitive coupling as an intermediary mechanism between the differential inductor and the LNA input stage. These capacitors act as mediators that block common-mode signals while allowing differential signals to pass through, thereby improving common-mode rejection and protecting the noise figure.
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 solution provides a low-noise, well-balanced differential output signal with improved common-mode rejection, suitable for wideband communication systems, reducing noise figure and minimizing chip area, thus enhancing the performance of receiver front ends in devices like mobile telephones.
Implementation Method 1
a center-tapped differential inductor for converting the single-ended input signal into a differential signal to be amplified
Implementation Method 2
a control terminal of a first one of the at least two transistors is coupled through a first capacitance to the first terminal of a second one of the at least two transistors
Data Source
AI summary
An RF amplifier can include a differential inductor for single-ended-to-differential signal conversion. With a center tap of the differential inductor coupled to signal ground and the RF input signal coupled to one of the end taps of the inductor, the negative of the RF input signal is obtained at the other end tap of the inductor. The differential RF signal produced can be coupled to a differential transistor amplifier that has cross-coupling capacitances, improving the signal balance of the differential output signal.