BAW Parallel-Resonance Band-Pass Filter for High-Q RF Integration

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Solution Overview

Problem

Existing RF filters in transceivers face challenges in achieving high quality factor (Q) performance, particularly in integrated chip implementations, as on-chip LC tanks are inadequate, and external SAW filters are not integrable due to size constraints.

Innovation Solution

A band pass filter circuit employing parallel resonance of a bulk acoustic wave (BAW) resonator is used, where the BAW resonator is coupled in parallel to the bias resistor and amplifier output, improving the quality factor by acting as a parallel resonant circuit instead of a series pass circuit.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If on-chip inductor/capacitor (LC) tanks are used for filtering, then integration is achieved, but high quality factor (Q) performance and rejection capability cannot be achieved

Engineering Contradiction:

Improveintegration capabilityVSAvoidquality factor performance

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent combines the BAW resonator with the amplifier output stage to form an integrated filter circuit. The BAW resonator is coupled in parallel to the bias resistor through the amplifier output, merging the filtering function with the existing amplifier structure. This integration approach achieves both on-chip integration and high Q performance by utilizing the superior rejection capability of BAW technology while maintaining manufacturability through standard integrated circuit fabrication processes.

Inventive Principle:

Principle #5Merging (Combining)

2Reliability

If external surface acoustic wave (SAW) filters are used to achieve desired rejection capability, then high quality factor (Q) performance is achieved, but integration on integrated chip is not possible due to size constraints

Engineering Contradiction:

Improverejection capabilityVSAvoidintegrability

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent embeds the BAW resonator structure within the integrated circuit chip, nesting the high-Q filtering element inside the amplifier circuit. The BAW resonator is coupled to the amplifier output and bias resistor, effectively placing a high-performance filter component within the integrated chip structure. This nesting approach enables the benefits of external SAW/BAW filter performance while achieving true on-chip integration.

Inventive Principle:

Principle #7Nested doll (Nesting)

Solution Approach 2:

The patent replaces the traditional mechanical/electrical LC tank filter structure with a BAW resonator-based filter. The BAW resonator uses acoustic wave resonance mechanisms to achieve high Q performance, substituting the conventional electrical resonance approach with acoustic resonance. This substitution enables high rejection capability while maintaining compact integrated chip implementation.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Device complexity

If series pass circuit configuration is used, then simpler implementation is achieved, but rejection capability of signals outside pass band is insufficient

Engineering Contradiction:

Improvecircuit configuration simplicityVSAvoidrejection capability

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent inverts the traditional series pass filter configuration by using a parallel resonator configuration. Instead of placing the BAW resonator in series with the signal path, it is coupled in parallel to the bias resistor through the amplifier output. This inversion of the circuit topology transforms the filter from a series pass configuration with limited rejection capability to a parallel configuration that provides superior out-of-band signal rejection while maintaining implementation simplicity.

Inventive Principle:

Principle #13The other way round (Inversion)

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 the rejection capability of signals outside the pass band region by two to four times compared to series configurations, providing improved filtering performance.

Implementation Method 1

A bulk acoustic wave (BAW) resonator is coupled in parallel to the bias resistor via the power source and the amplifier output. The BAW resonator and the amplifier output forms a band pass filter to filter the AC waveform received at the amplifier input

Methodology Applied

Scientific EffectParallel resonance: Resonance

Implementation Method 2

A bulk acoustic wave (BAW) resonator is coupled in parallel to the bias resistor via the power source and the amplifier output

Methodology Applied

Scientific EffectBulk acoustic wave: Acoustic Radiation Pressure

Data Source

PatentUS20180191331A1Band pass filter utilizing parallel resonance of BAW resonator

Publication Date: 2018.07.05 TEXAS INSTRUMENTS INC

AI summary

A circuit includes an amplifier having an input that receives an alternating current (AC) waveform and an output that is coupled to a power source via a bias resistor. A bulk acoustic wave (BAW) resonator is coupled in parallel to the bias resistor via the power source and the amplifier output. The BAW resonator and the amplifier output forms a band pass filter to filter the AC waveform received at the amplifier input and to provide a filtered AC waveform at the amplifier output.