ST25R3911B datasheet(33/116 Pages) STMICROELECTRONICS

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Adjust regulators

When this command is sent the power supply level of VDD is measured in maximum load conditions and the

regulated voltage reference is set 250 mV below this measured level to ensure maximum possible stable

regulated supply (see Section 1.2.11 Power supply system). The use of this command increases the system

PSSR.

At the beginning of execution of the command, both the receiver and transmitter are switched on to have the

maximum current consumption, and the regulators are set to their maximum regulated voltage (5.1 V in case of 5

V supply and 3.4 V in case of 3.3 V supply). After 300 μs VSP_RF is compared to VDD, if is not at least 250 mV

lower the regulator setting is reduced by one step (120 mV in case of 5 V supply and 100 mV in case of 3.3 V

supply) and measurement is done after another 300 μs. The procedure is repeated until VSP_RF drops at least

250 mV below VDD, or until the minimum regulated voltage (3.9 V in case of 5 V supply and 2.4 V in case of 3.3 V

supply) is reached.

Duration time: 5 ms max.

This command is accepted if en (bit 7 of the Operation control register) is set and Xtal oscillator frequency is

stable.

This command is not accepted when the external definition of the regulated voltage is selected in the Regulator

voltage control register(bit reg_s is set to H).

Direct command chaining is not possible.

IRQ due to termination of direct command is produced after command execution is terminated.

Calibrate modulation depth

Starts a sequence that activates the transmission, measures the modulation depth and adapts it to comply with

the modulation depth specified in the AM modulation depth control register. When calibration procedure is

finished result is displayed in the same register. Refer to Section 1.2.20 AM modulation depth: definition and

calibration for details about setting the AM modulation depth and running this command.

Duration time: 275 μs max.

This command is accepted when en (bit 7 of the Operation control register) is set and Xtal oscillator frequency is

stable.

Direct command chaining is not possible.

IRQ due to termination of direct command is produced after command execution is terminated.

Calibrate antenna

Sending this command starts a sequence that adjusts the parallel capacitances connected to TRIMx_y pins so

that the antenna LC tank is in resonance. See Section 1.2.21 Antenna tuning for details.

Duration time: 250 μs max.

This command is accepted when en (bit 7 of the Operation control register) is set and Xtal oscillator frequency is

stable.

Measure phase

This command measures the phase difference between the signals on the RFO outputs and the signals on the

RFI inputs and stores the result in the A/D converter output register.

During execution of the direct command Measure Phase the transmitter and Phase Detector are enabled, the

Phase Detector output is multiplexed on the input of A/ D converter, which is set in relative mode. Since the A/D

converter range is from 1/6 VSP_A to 5/6 VSP_A the actual phase detector range is from 30º to 150º. Values

below 30º result in FFh, while values above 150º result in 00h. One LSB of the A/D conversion output represents

0.13% of carrier frequency period (0.468°). The result of A/D conversion is in case of 90º phase shift in the middle

of range (1000 0000b or 0111 1111b). A value higher than 1000 0000b means that phase detector output voltage

is higher than VSP_A/2, which corresponds to case with phase shift lower than 90º. In the opposite case, when the

phase shift is higher than 90º, the result of A/D conversion is lower than 0111 1111b. For example, the phase

difference of 135º shown in Figure 7 results in 0.75 VSP_A, result stored in A/D converter is 31d (1Fh).

The phase measurement result can be calculating using the following formulas:

ST25R3911B

Application information

DS11793 - Rev 6

page 33/116

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