5.20.6 Frequency Hopping Spread Spectrum Systems (FHSS)

Due to the very fast locking properties of the PLL, the CC1020 device is also very suitable for frequency hopping systems. Hop rates of 1 to 100 hops/s are commonly used depending on the bit rate and the amount of data to be sent during each transmission. The two frequency registers (FREQ_A and FREQ_B) are designed such that the ‘next’ frequency can be programmed while the ‘present’ frequency is used. The switching between the two frequencies is done through the MAIN register. Several features have been included to do the hopping without a need to re-synchronize the receiver. For more details, refer to Application Note AN014 Frequency Hopping Systems (SWRA077).

In order to implement a frequency hopping system with the CC1020 device, do the following:

Set the desired frequency, calibrate and store the following register settings in non-volatile memory:

Repeat the calibration for each desired frequency. VCO_CAL_CURRENT[5:0] is not dependent on the RF frequency and the same value can be used for all frequencies.

When performing frequency hopping, write the stored values to the corresponding TEST1, TEST2 and TEST3 registers, and enable override:

CHP_CO[3:0] is the register setting read from CHP_CURRENT[3:0], VCO_AO[4:0] is the register setting read from VCO_ARRAY[4:0] and VCO_CO[5:0] is the register setting read from VCO_CAL_CURRENT[5:0].

Assume channel 1, defined by register FREQ_A, is currently being used and that the CC1020 device should operate on channel 2 next (to change channel simply write to register MAIN[6]). The channel 2 frequency can be set by register FREQ_B which can be written to while operating on channel 1. The calibration data must be written to the TEST1-3 registers after switching to the next frequency. That is, when hopping to a new channel write to register MAIN[6] first and the test registers next. The PA should be switched off between each hop and the PLL should be checked for lock before switching the PA back on after a hop has been performed.