SPIRIT1 datasheet(45/94 Pages) STMICROELECTRONICS

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SPIRIT1

Transmission and reception

Doc ID 022758 Rev 3

45/94

Figure 8.

Output power ramping configuration

The set of 8 levels is used to shape the ASK signal. In this case, the modulator works as a

counter that counts up when transmitting a one and down when transmitting a zero. The

counter counts at a rate equal to 8 times the symbol rate (in this case, the field

PA_RAMP_STEP_WIDTH is not used). This counter value is used as an index for the

lookup in the levels table in Figure 8 to associate the relevant POUT value. Therefore, in

order to utilize the whole table, PA_LEVEL_MAX_INDEX should be 7 when ASK is active.

The real shaping of the ASK signal is dependent on the configuration of the PA_LEVEL_x

registers. Figure 8 shows some examples of ASK shaping.

For OOK modulation, the signal is abruptly switched between two levels only, these are

PA_LEVEL_0 and PA_LEVEL_x, with x=PA_LEVEL_MAX INDEX.

The 2-bit CWC field in the PA_POWER register bank can be used to tune the internal

capacitive load of the PA (up to 3.6 pF in steps of 1.2 pF) in order to optimize the

performance at different frequencies.

9.2

RF channel frequency settings

RF channels can be defined using the CHSPACE and CHNUM registers.

The channel center frequency can be programmed as:

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