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Question What is TCXO? Solution TCXO is a temperature controlled crystal oscillator. In general, the accuracy of an oscillator is specified in parts per million. This means a given oscillator will be off so many parts per each million of its oscillations or “ticks”. Taking the VXI world as an example, the requirement is that each slot zero controller be capable of delivering a 10MHz reference that is off by no more than 100PPM. This means that to be compliant with the VXI specification, a slot zero controller must deliver 10 million oscillations +/-1000 ticks every second. Any more error would be non-compliance. TCXO is a crystal used to deliver superior clock precision and accuracy. Specifically, a temperature controlled crystal oscillator is guaranteed to operate at 10PPM. In simplest terms, it works by using a feedback loop to adjust the oscillator output based on ambient temperature. Temperature is a key parameter which affects the accuracy of a clock. For those applications which require superior clock performance, VTI Instruments provides TCXO as an option on several products. The VM2164 is a VXI based counter timer device which can be upgraded to use an onboard TCXO oscillator. The EX2500A, a VXI slot zero controller, typically delivers the standard VXI 10MHz reference with an error of 50PPM, but can be optionally equipped to utilize temperature controlled crystal oscillator which delivers 10MHz at 10PPM.