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Term: Series vs. Parallel Load Resonance Definition: 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 antiresonance). The crystals used in these two types of modes are physically the same crystal, but calibrated to slightly different frequencies. 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 circuit’s discrete load capacitance, stray board ca-pacitance, 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 the equation below:
Cardinal Components
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