Tunable BAW Filter Resonator Frequency Shift
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Solution Overview
Problem
Acoustic resonators in mobile devices experience degraded signal quality and increased insertion loss at the frequency edges of their passbands, leading to poorer communication performance, especially when channels are allocated near the upper or lower corners of the frequency band.
Innovation Solution
A tunable BAW filter device is implemented with a high impedance voltage bias network that applies a non-zero DC bias voltage to BAW resonators, shifting their resonance frequency towards the center of the frequency band, thereby improving insertion loss and reducing current consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If channels are allocated near the upper or lower corners of the frequency band, then more channels can be accommodated in the frequency band, but insertion loss increases and signal quality degrades
Solution Approach 1:
The patent applies dynamic frequency tuning by adjusting the resonance frequency of BAW resonators based on the allocated channel position. When a channel near the frequency band edge is allocated, the resonator's resonance frequency is shifted to compensate for the increased insertion loss, thereby maintaining signal quality while enabling edge channel allocation.
Solution Approach 2:
The invention changes the electrical parameter (DC bias voltage) of the BAW resonator to dynamically adjust its resonance frequency. By applying a controllable DC voltage, the resonator's operating point is shifted, which compensates for the frequency-dependent insertion loss and enables reliable operation at frequency band edges.
2Reliability
If DC bias voltage is applied to shift resonance frequency, then insertion loss is improved, but current consumption increases
Solution Approach 1:
The patent applies partial DC bias voltage only when and where needed - specifically when channels near the frequency band edges are allocated. The bias voltage is applied selectively to specific BAW resonators based on the allocated channel position, rather than continuously to all resonators, thereby reducing overall current consumption while maintaining insertion loss performance when required.
Solution Approach 2:
The DC bias voltage is applied in a periodic or event-driven manner based on channel allocation changes. When the allocated channel requires frequency compensation, the bias is applied; when channels are allocated in the center of the frequency band where insertion loss is already acceptable, the bias is reduced or removed, creating a dynamic energy-saving operation mode.
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 solution enhances signal quality by minimizing insertion loss and current consumption, particularly in channels near the frequency edges, resulting in improved communication performance across the entire frequency band.
Implementation Method 1
An FBAR, for example, includes a piezoelectric layer between a first (bottom) electrode and a second (top) electrode formed over a cavity in a substrate
Implementation Method 2
FBARs resonate at GHz frequencies, and are thus relatively compact, having thicknesses on the order of microns
Data Source
AI summary
A tunable BAW filter device operating in an allocated channel of a predetermined frequency band includes a voltage source and multiple BAW resonators. The voltage source selectively provides non-zero DC bias voltage based on a location of the allocated channel within the frequency band. Each BAW resonator has a resonance frequency, and includes a bottom electrode, a piezoelectric layer and a top electrode disposed over the piezoelectric layer, the top electrode being electrically connected to the voltage source via a resistor. The voltage source is activated, applying the non-zero DC bias voltage to the top electrode of each BAW resonator, when the location of the allocated channel is near an upper or lower corner of the frequency band. The resonance frequency of each BAW resonator is shifted in response to the non-zero DC bias voltage toward a center of the frequency band, improving insertion loss of the BAW filter device.