AS3911 datasheet(57/149 Pages) AMSCO

57 / 149 page

ams Datasheet, Confidential: 2013-Oct [2-03]

AS3911 – 57

Appl icatio n I n f o rm a t i o n

IRQ due to termination of direct command is produced after

command execution is terminated.

Calibrate Antenna

Sending this command starts a sequence which adjusts the

parallel capacitances connected to TRIMx pins so that the

antenna LC tank is in resonance. See Antenna Tuning for details.

Duration time: 250 μs max.

This command is accepted in case 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. 1 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). 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 depicted in Figure 18

results in 0.75 VSP_A, result stored in A/D converter is 31d (1Fh).

AS3911 데이터시트(PDF) 57 Page - ams AG