ECM2A Series Crystal

Frequency Tolerance or Calibration Accuracy

The amount of frequency deviation from a specified center frequency at ambient temperature (referenced at 25°C). This parameter is specified with a maximum and minimum frequency deviation, expressed in percent (%) or parts per million (ppm). This deviation is associated with a set of operating conditions including: Load Capacitance and Drive Level.

Series vs. Parallel Load Resonance

A crystal can be used in an oscillator circuit to operate in either of two resonant modes: Series Resonance or Parallel Load Resonance (also known as anti-resonance). The crystals used in these two types of modes are physically the same crystal, but calibrated to slightly different frequencies. See the crystal reactance curve for a graphical presentation of this effect. When a crystal is placed into an oscillator circuit,they oscillate together at a tuned frequency. This frequency is dependent upon the crystal design and the amount of Load Capacitance, if any, the oscillator circuit presents to the crystal. Specified in picofarads (pF), Load Capacitance is comprised of a combination of the circuits discrete load capacitance, stray board capacitance, and capacitance from semiconductor miller effects. When an oscillator circuit presents some amount of load capacitance to a crystal, the crystal is termed "Parallel Load Resonant", and a value of Load Capacitance must be specified. If the circuit does not exhibit any capacitive loading, the crystal is termed "Series Resonant", and no value of Load Capacitance is specified. The "Parallel Load Resonant" operating frequency of a quartz crystal is based on this equation.

The resistive element, measured in ohms, of a crystal device. At the frequency found in Equation 1, the motional inductance (L₁)and motional capacitance (C₁) are of equal ohmic value but are exactly opposite in phase. The net result is that they cancel one another and only a resistance remains in the series leg of the equivalent circuit. The ESR measurement is made only at the series resonant frequency (F_S), not at some predetermined parallel resonant frequency (F_L). Crystal resistance measured at some parallel load resonant frequency is often called the "effective" resistance.

The static capacitance between the crystal terminals. Measured in picofarads (pF), Shunt Capacitance is present whether the device is oscillating or not (unrelated to the piezoelectric effect of the quartz). Shunt Capacitance is derived from the dielectric of the quartz, the area of the crystal electrodes, and the capacitance presented by the crystal holder.

The Mode of Operation of a quartz device is one of the factors that will determine the frequency of oscillation. For "AT" cut quartz crystals, over tone modes are at odd frequency harmonics. For example, a crystal may operate at its fundamental frequency of 10 MHz, or at odd harmonics of approximately 30MHz (Third Overtone), 50MHz (Fifth Over tone), and 70 MHz (Seventh Overtone).

The minimum and maximum temperatures that the device can be stored or exposed to when in a non-oscillation state. After exposing or storing the device at the minimum or maximum temperatures for a length of time, all of the operating specifications are guaranteed over the specified Operating Temperature Range.

A function of the driving or excitation current flowing through the crystal. The Drive Level is the amount of power dissipation in the crystal, expressed in microwatts or milliwatts. Maximum power is the most power the device can dissipate while still maintaining operation with all electrical parameters guaranteed. Drive level should be maintained at the minimum levels necessary to initiate proper start-up and assure steady state oscillation. Excessive drive level can cause poor aging characteristics and crystal damage.

The systematic change in frequency with time due to internal changes in the crystal. Aging is often expressed as a maximum value in parts per million per year [ppm/yr]. The rate of aging is typically greatest during the first 30 to 60 days after which time the aging rate decreases. The following factors effect crystal aging: adsorption and desorption of contamination on the surfaces of the quartz, stress relief of the mounting and bonding structures, material outgassing, and seal integrity.