SAW Integrated Balun for Out-of-Band Rejection in RF Front Ends
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Solution Overview
Problem
Existing wireless devices face interference from out-of-band signals due to intermodulation and harmonic interference, which masks desired signals and desensitizes receivers, particularly in GPS receivers, due to the lack of effective filtering and additional noise introduced by balun circuits in differential receivers.
Innovation Solution
Incorporating a surface acoustic wave (SAW) filter that provides balun functionality without a separate balun circuit element, converting single-ended inputs to differential outputs, and eliminating the need for impedance matching circuits between the SAW filter and low noise amplifier, thereby reducing noise and loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a separate balun circuit element is used to convert single-ended inputs to differential outputs, then the conversion function is achieved, but additional noise and loss are introduced
Solution Approach 1:
The patent combines the balun functionality directly into the SAW filter structure by configuring the interdigital transducer electrodes such that one electrode receives the single-ended input signal while the other electrode outputs the differential signal. This integration eliminates the need for a separate balun circuit, thereby reducing additional noise and signal loss that would be introduced by discrete balun components.
Solution Approach 2:
The SAW filter is designed to perform multiple functions simultaneously: it provides both frequency filtering and balun conversion in a single device. The interdigital transducer electrode configuration enables the filter to convert single-ended inputs to differential outputs while maintaining its primary filtering function, eliminating the need for separate conversion circuits.
2Reliability
If impedance matching circuits are added between the SAW filter and low noise amplifier, then impedance matching is improved, but device complexity and size increase
Solution Approach 1:
The patent integrates impedance matching functionality directly into the SAW filter design by configuring the interdigital transducer electrodes and bus bars to provide both filtering and impedance transformation. This eliminates the need for separate impedance matching circuits, thereby reducing device complexity and size while maintaining proper impedance matching between the filter and low noise amplifier.
3Object-affected harmful factors
If additional filtering circuits are added to reject out-of-band signals, then signal rejection is improved, but device complexity and size increase
Solution Approach 1:
The SAW filter is designed to perform multiple functions simultaneously: it provides both frequency filtering and balun conversion in a single device. The interdigital transducer electrode configuration enables the filter to convert single-ended inputs to differential outputs while maintaining its primary filtering function, eliminating the need for separate conversion circuits.
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 signal rejection by up to 20 dB, improving the sensitivity of wireless devices to target frequencies while reducing the size and complexity of front-end modules by eliminating additional circuitry, thus minimizing interference from out-of-band signals.
Implementation Method 1
A surface acoustic wave resonator of a surface acoustic wave filter typically includes an interdigital transductor electrode on a piezoelectric substrate. A surface acoustic wave resonator is arranged to generate a surface acoustic wave.
Implementation Method 2
The first interdigital transducer electrode may be single-ended with a first input bus bar configured to receive an input signal and a second input bus bar connected to ground. The second interdigital transducer electrode may be differential with a first output bus bar connected to a first output terminal and a second output bus bar connected to a second output terminal.
Data Source
AI summary
A front-end module may include an acoustic wave filter with a first and second interdigital transducer electrode, and a low noise amplifier (LNA) that converts a differential input to a single-ended output with respect to ground. The first interdigital transducer electrode may be single-ended with a first input bus bar configured to receive an input signal and a second input bus bar connected to ground. The second interdigital transducer electrode may be differential with a first output bus bar connected to a first output terminal and a second output bus bar connected to a second output terminal. The LNA may have a differential input connected to the acoustic wave filter, a first input transistor that receives a first signal from the first output terminal of the acoustic wave filter, and a second input transistor that receives a second signal from the second output terminal of the acoustic wave filter.