Crystal, resonator or oscillator: which clock source fits?

Sinuss Redactie

Block diagram of an IC with an internal oscillator stage, external crystal and two load capacitors, beside a complete oscillator with supply and enable feeding a clock into the IC.

A crystal, ceramic resonator and complete oscillator may list the same frequency, but they are not interchangeable. A crystal or resonator works with an oscillator circuit inside the IC. A complete oscillator includes its active circuit and supplies a clock signal.

Check these eight points

  1. Input type: does the IC expect a crystal/resonator or an external clock?
  2. Frequency: use only values and modes permitted by the IC documentation.
  3. Tolerance and stability: include initial tolerance, temperature, ageing and supply effects.
  4. Load capacitance: external and stray capacitance influence a crystal's frequency.
  5. Drive level: excessive drive can shift frequency or stress the crystal.
  6. Start-up margin: verify ESR, negative resistance and start-up with the reference design.
  7. Oscillator output: supply, logic level, load and enable function matter.
  8. Package and layout: verify footprint, pinout, short traces, grounding and noise sources.

Do not replace a crystal from frequency and package alone. Compare manufacturer part number and all electrical parameters, including capacitors and layout around the exact IC.

View crystals, resonators or oscillators, then check the datasheet and reference schematic for the exact IC.