SN74HC74N Logic IC_CSTLS4M00G53-A0 Introduction

Kim Wong, vice president and general manager of TI's High-Speed Data and Clocking Group, said: "The clocking requirements for future communications infrastructures will far exceed the device performance of current quartz crystal resonators. By integrating TI's BAW resonators directly into clocking devices , we can achieve ultra-low jitter performance and resiliency to meet the increasingly stringent requirements for data pipeline resistance to vibration and shock in the process of communication transformation.”

The TI BAW oscillator is an electronic oscillator circuit that utilizes the piezoelectric effect to generate a stable electronic signal through the mechanical resonance of a vibrating miniature acoustic resonator (BAW). This precise high-frequency signal provides a clock and timing reference for electronic systems.

SN74HC74N Logic IC_CSTLS4M00G53-A0

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In order to gain an in-depth understanding of TI's new breakthrough in BAW technology, let's start with the principle of BAW filter: . For the first time in the industry, TI uses this technology for integrated clock functions. • In the past, BAW resonator technology has been used to filter signals in communication technologies such as smartphones.

Ray Upton, TI's vice president of connected microcontrollers, explained that new technologies are critical to "moving large amounts of data in a stable manner," improving high-performance communications. .

The most basic structure of the BAW filter is that two metal electrodes sandwich a piezoelectric film (the thickness of the Quartz substrate is 2um at 2GHz), and the acoustic wave oscillates in the piezoelectric film to form a standing wave.

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SN74HC74N Logic IC_CSTLS4M00G53-A0

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The overall effect of this structure is equivalent to contact with air, and most of the sound waves are reflected back. This structure is called BAW-SMR (Solidly Mounted Resonator), as shown below. The reflector consists of several layers of alternating high and low impedance layers. For example, the first layer has a large acoustic wave impedance, the second layer has a small acoustic wave impedance, and the third layer has a large acoustic wave impedance, and the thickness of each layer is λ/4 of the acoustic wave, so that most of the wave will be reflected back and superimposed with the original wave. One way is to form a Bragg reflector under the oscillating structure to reflect sound waves into the piezoelectric layer.

When asked why nobody in the industry has built something like a BAW resonator, Upton said, "It's very difficult to develop. But it's not easy to convert electrical energy into mechanical acoustics while keeping the signal stable and robust within a clean clock." TI has been involved in MEMS research for many years.

. In order to keep the acoustic wave in the piezoelectric film to oscillate, there must be sufficient isolation between the oscillating structure and the external environment to obtain a small loss and a large Q value. On the other side of the oscillating structure, the acoustic impedance of the piezoelectric material is not much different from that of other substrates (such as Si), so the piezoelectric layer cannot be deposited directly on the Si substrate. The propagation speed of sound waves in solids is ~5000m/s, which means that the acoustic impedance of solids is about 105 times that of air, so 99.995% of the sound wave energy will be reflected back at the boundary between the solid and the air, which is the same as the original wave (incident wave). together to form a standing wave.

SN74HC74N Logic IC_CSTLS4M00G53-A0

The BAW filter is more suitable for frequencies above 2.5GHz. The manufacturing process of the BAW filter is also very consistent with the existing IC manufacturing process, and is suitable for overall integration with other active circuits. .

TI's newest SimpleLink™ multi-standard MCU with ?BAW technology can be integrated into low-power wireless RF devices, such as low-power crystalless Bluetooth and Zigbee? technology, thereby reducing wireless RF failures caused by external crystals.

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