How to select the proper quartz crystal to meet a designs timing budget

There are five timing budget parameters which influence the total system timing error of a quartz crystal and oscillator combination:

  1. Frequency tolerance, also known as calibration accuracy, is the amount of frequency deviation from a specified center
    frequency at ambient temperature (referenced at 25°C).
  2. Frequency Stability is the amount of frequency deviation from the ambient temperature frequency over the operating
    temperature range. This deviation is associated with a set of operating conditions including: Operating Temperature Range, Load
    Capacitance, and Drive Level.
  3. Aging is the systematic change in frequency with time due to internal changes in the crystal which is related to the crystal
    contamination and drive level. Over time, particles drop off or fall onto the quartz surface, hence slightly changing the resonant
  4. Load capacitance (CL) is the fourth parameter to consider. A crystal can be characterized for either series or parallel load
    resonant mode of operation. Both modes are physically the same; they are just tuned to operate in a different area of the crystal
    reactance curve.
  5. Oscillator accuracy is the fifth parameter to consider. Many times, this parameter is ignored, but process shifts in the silicon,
    temperature and voltage can have an effect on the center frequency. This variation is dominated by the process shift parameters
    and can be minimized by the amount of internal load capacitance in the oscillator and the trim sensitivity of the quartz crystal.
Refer to application note AN-803  and AN-832 for more details on timing budget and accuracy for IDT timing clock products. For other questions not addressed by the Knowledge Base, please submit a technical support request.  


Title Other Languages Type Format File Size Date
Application Notes & White Papers
AN-803 Crystal Timing Budget and Accuracy for IDT Timing Clock Products Application Note PDF 44 KB May 7, 2014
AN-832 Timing Budget and Accuracy Application Note PDF 48 KB May 5, 2014