The Importance of ESR in Quartz Crystal Circuits - EuroQuartz
November 23, 2020
ESR (Equivalent Series Resistance) is the sum of in-phase AC resistance. It includes resistance of the dielectric, plate material, electrolytic solution, and terminal leads at a particular frequency. ESR acts like a resistor in series with a capacitor.
The first thing to state is that this is not a measured parameter, it is a figure derived from the equivalent crystal circuit. However, the actual measured parameter of resonant resistance equates fairly well to it. The ESR of a crystal is the resistance exhibited at series resonance, it is proportional to the power dissipated within the crystal.
To put it simply it indicates the amount of power required by the crystal to resonate at it’s given frequency. The simple rule of thumb is, the bigger the piece of quartz the lower the ESR, which can be clearly seen if you compare two sizes of crystal shown below.
Some of the more popular simple oscillator circuits can refuse to start oscillation if a crystal with a too high an ESR is employed or may not operate consistently in application. This can result in unreliability, caused by batch variation failures, because there will be an optimum ESR for any circuit and if this optimum happens to fall within the middle of a crystal batch spread then a percentage of the crystals may fail as the circuit has insufficient gain to drive the higher ESR crystals.
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