STS1TX datasheet(36/70 Pages) STMICROELECTRONICS

36 / 70 page

Transmission and reception

STS1TX

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DocID025109 Rev 1

Figure 7. 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 7 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 7 shows some examples of ASK shaping.

Using the a frequency modulation, the output power is configured by PA_LEVEL_x, with

x=PA_LEVEL_MAX_INDEX.

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.

The output power are reported in Table 26: PA_level.

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