The tuning range improvement of voltage controlled crystal oscillators by using multiple crystals in parallel

This paper presents a wide tuning range voltage controlled crystal oscillator (VCXO) that uses several crystals in parallel. A number of crystals are connected in parallel to increase the tuning range of the oscillator. The parallel crystal combination is shown to be equivalent to a single crystal with a wide tuning range. This arrangement is ideal for applications requiring a larger tuning range. Generalized design equations are derived showing the tuning range relationship to the number of crystals in the circuit. This extended tuning range is demonstrated up to five crystals in parallel. The overall performances of wide tuning range VCXO circuits with multiple crystals are presented.