The CC1312PSIP device has several internal system clocks.

The 48 MHz SCLK_HF is used as the main system (MCU and peripherals) clock. This can be driven by the internal 48 MHz RC Oscillator (RCOSC_HF) or in-package 48 MHz crystal (XOSC_HF). Note that the radio operation runs off the included, in-package 48 MHz crystal within the module.

Production calibration of the 48 MHz crystal frequency

The crystal frequency is calibrated in production of the SIP module at room temperature to reduce the initial frequency error to a minimum. This is done by setting the internal capacitor array to the value that gives closest to 48 MHz.

Software TCXO

In addition to this initial analog frequency error removal by changing the internal load capacitance, the CC1312PSIP is also implementing a feature called Software TCXO. Software TCXO is not affecting the 48 MHz crystal frequency itself, but it is using the know initial frequency error and a model of the temperature behavior of the 48 MHz crystal to generate a very accurate RF frequency. The software TCXO feature works as following: In the final production test of the SIP module, the RF frequency is measured and the RF frequency error (proportional to the ppm error) caused by the remaining error of the 48 MHz crystal is stored in factory flash area (FCFG). The internal PLL that is generating the RF frequency is using the 48 MHz crystal as a reference frequency, so the temperature drift of the crystal - in ppm (parts per million) will give the same error for the RF frequency. The temperature drift for the 48 MHz crystal can be modelled as a third order equation and used together with the internal temperature sensor, this would give a good average temperature estimation of the 48 MHz crystals used in the CC1312PSIP. The coefficients for the third order equation is defined in the sysconfig configuration software tool and firmware in the CC1312PSIP will then automatically correct the RF frequency in RX and TX by taking into account the initial frequency error as well as the temperature drift.

SCLK_LF is the 32.8 kHz internal low-frequency system clock. It can be used by the Sensor Controller for ultra-low-power operation and is also used for the RTC and to synchronize the radio timer before or after Standby power mode. SCLK_LF can be driven by the internal 32.8 kHz RC Oscillator (RCOSC_LF) or the included, in-package 32.768 kHz crystal within the module. When using a crystal or the internal RC oscillator, the device can output the 32 kHz SCLK_LF signal to other devices, thereby reducing the overall system cost.

RTC temperature compensation

The CC1312PSIP includes a firmware function that will improve the RTC (Real Time Clock) accuracy when using the in-package 32.768 kHz crystal as a basis for the RTC. In the final production test of the SIP module, the RTC frequency is measured and the error is stored in the factory flash area (FCFG). The temperature drift of the 32.768 kHz crystal can be modelled as a second order equation and the coefficient for this equation is defined in the sysconfig configuration software tool. Firmware in the CC1312PSIP will then use the temperature sensor in the CC1312PSIP, the initial frequency error stored in factory flash area (FCFG) and the model for temperature drift to calculate a more accurate RTC.