Historically, frequency tuning has been achieved through pulling the frequency using a voltage input. This type of frequency control device is called a VCXO (voltage controlled oscillator). A large number of TCXO (temperature compensated oscillator) applications use a voltage control function for frequency tuning during operation. These devices are often called VCTCXOs or TCVCXOs. An alternative method for tuning frequency is by use of a digital input.
Several SiTime Elite Platform™ Super-TCXO™ families, listed in Table 1, offer both voltage control and digital control for frequency tuning. This application note provides information on the DCO mode (digitally controlled oscillator mode) of these precision Super-TCXO families which support digital input through an I2C digital interface. Using the DCO mode, the output frequency can be continuously pulled within the specified pull range. The pull range can be changed in-system to one of 16 available pull range options, from ±6.25 to ±3200. Additionally, DCO mode allows users to control the output enable (OE) state of the device through the writes to the device’s registers (corresponding part number option has to be selected).
