BAW Heterodyne Receiver Filtering for Image Rejection
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Solution Overview
Problem
Heterodyne communication systems face challenges in suppressing image frequencies and high-level 'blocking' signals, particularly in WCDMA and GSM transmission, due to the difficulty of integrating selective filters with high selectivity and quality factors within semiconductor products.
Innovation Solution
A heterodyne receiving circuit utilizing BAW-type tunable resonators with master/slave filter architectures and PLL-type frequency control loops for adjusting band pass and narrow band filters, allowing for full integration on a semiconductor substrate and effective suppression of image frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If SAW-type resonators are used for filtering, then filtering performance is achieved, but integration in semiconductor product is difficult
Solution Approach 1:
The patent replaces surface acoustic wave (SAW) resonators with bulk acoustic wave (BAW) resonators. BAW resonators use bulk acoustic waves propagating through the thickness of a piezoelectric layer rather than surface waves, enabling direct integration with semiconductor fabrication processes while maintaining high filtering performance and quality factors.
Solution Approach 2:
The patent changes the physical parameters of the resonator structure by using piezoelectric materials with specific acoustic properties and configuring the resonator geometry to support bulk acoustic modes. This allows the resonator to be fabricated using standard semiconductor techniques while achieving the required filtering characteristics.
2Reliability
If narrow band filter is used to suppress image frequency, then suppression performance is improved, but device complexity and integration difficulty increase
Solution Approach 1:
The patent combines the band-pass filtering function and the image frequency rejection function into a single BAW resonator structure. The resonator is designed with specific parallel and series resonance frequencies that simultaneously provide the desired passband characteristics and stopband rejection, eliminating the need for separate filtering stages.
Solution Approach 2:
The BAW resonator is designed to perform multiple functions: it acts as a band-pass filter for the desired signal frequency while simultaneously providing image frequency rejection. This multi-functional design simplifies the overall receiver architecture by reducing the number of discrete filtering components required.
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 enables efficient suppression of image frequencies and channel selection within a single semiconductor substrate, improving the performance and integration of heterodyne communication systems by maintaining high quality factor and flexibility in resonator characteristics.
Implementation Method 1
BAW-type resonators with piezoelectric material layers
Implementation Method 2
bulk acoustic wave (BAW) type elements
Data Source
AI summary
A heterodyne receiving circuit for a digital communication system including a first band pass filter receiving a signal from an antenna, an amplifying circuit and a second narrow band pass filter for selecting one particular channel within a band of frequencies. The two filters are carried out with integrated BAW-type tunable resonators which can be adjusted, respectively, by a first electrical signal and a second electrical signal generated by two PLL-type frequency control loops. The second frequency control loop has a variable division factor for the purpose of selecting one particular channel within said band of frequencies. In addition, the receiving circuit includes a mixer for mixing the signal generated at the output of said second filter with a local oscillation frequency in order to produce an intermediate frequency. The division factor is controlled by a digital processing of the intermediate frequency.