SNAA390 july   2023 LMK6C , LMK6D , LMK6H , LMK6P

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Test Standards and Test Setup
    1. 2.1 Test Standards
    2. 2.2 Test Setup in Vibration Lab
  6. 3Sinusoidal Vibration, Random Vibration, and Mechanical Shock Tests
    1. 3.1 Sinusoidal Vibration Test
      1. 3.1.1 Procedure for Sinusoidal Vibration Test
      2. 3.1.2 Results From Sinusoidal Vibration Test
    2. 3.2 Random Vibration Test
      1. 3.2.1 Procedure for Random Vibration Test
      2. 3.2.2 Results From Random Vibration Test
    3. 3.3 Mechanical Shock Test
      1. 3.3.1 Procedure for Mechanical Shock Test
      2. 3.3.2 Results From Mechanical Shock Test
  7. 4Comparison of BAW Oscillator Vibration Performance With Crystal Oscillator
    1. 4.1 Comparison Test Setup
    2. 4.2 Comparison Test Results
  8. 5Summary
  9. 6References

1 Introduction

The sensitivity to vibration and shock is a key consideration when designing systems with a crystal- or MEMS-based clock oscillator. Devices with high sensitivity to vibration can have a detrimental impact on the overall system performance, affecting the phase noise and jitter, frequency stability, and long-term reliability. The clock oscillator needs to provide a stable clock with strong resistance against acceleration forces, vibration, and shock, as resistance provides stability throughout the product life cycles under process and temperature variations.

The two important parameters for quantifying vibration are the acceleration force and vibration frequency applied to the devices. To quantify shock, acceleration force and the time duration for which the peak acceleration is applied are used. Vibrations and mechanical shock affect resonators by inducing noise and frequency drift, degrading system performance over time. In oscillators, vibration and shock are common causes of elevated phase noise and jitter, frequency shifts and spikes, or even physical damage to the resonator and resonator package. These degradations of phase noise and jitter directly impact the system performance. Typically, external disturbances couple into the micro resonator through the package. Since crystal oscillators fundamentally rely on the vibration and mechanical resonance of a piezoelectric material, external disturbances can couple into the device and degrade oscillator performance. Mechanical shocks of sufficient magnitude can also cause irreversible frequency shifts at the output of the crystal oscillator.

TI BAW oscillators fare better, when compared to quartz-based oscillators. TI’s BAW oscillators are more immune to vibration and mechanical shock due to the smaller mass (by orders of magnitude) of the resonator and higher resonance frequency. The force applied to the device from external acceleration is much smaller due to smaller mass. The immunity of the device is further enhanced by the semiconductor manufacturing process of the BAW resonator. The BAW piezo and metal layers are surrounded by Bragg mirrors, which shield the resonator from environmental stresses. The BAW oscillator also includes a wafer-level encapsulation for making the oscillator a robust and reliable product. TI’s dual-Bragg BAW resonators contains no moving parts, which provides resilience against environmental stress with improved device reliability.

Vibration sources are present in many end-applications including hand-held mobile devices, cooling fans in equipment chassis, factory automation equipment, construction equipment, moving vehicles or aircraft. The following table provides examples of the vibration levels at different environment conditions.

Table 1-1 Typical Acceleration Levels in Various Environments
Environment(1) Typical acceleration (g)
Buildings quiescent 0.02 rms
Tractor-trailer (3 to 80 Hz) 0.2 peak
Armored personnel carrier 0.5 to 3 rms
Ship - calm seas 0.02 to 0.1 peak
Ship - rough seas 0.8 peak
Railroads 0.1 to 1 peak
Propeller aircraft 0.3 to 5 rms
Helicopter 0.1 to 7 rms
Jet aircraft 0.02 to 2 rms
Missile - boost phase 15 peak

A LMK6x oscillator from Texas Instruments is used to quantify the vibration and shock performance of BAW oscillators. The devices are subjected to sinusoidal vibrations at various frequencies along the X, Y and Z directions. The tests are repeated along each axis with random vibration profiles. The final test measures the transient frequency deviation of the units during operation in response to mechanical shock. Phase noise (including spurs) and frequency shift data are then recorded during these tests.