AS3911 datasheet(136/149 Pages) AMSCO

136 / 149 page

AS3911 – 136

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

A p pl i c at io n I n f o r m at i o n

Antenna Tuning Using Direct Command ‘Calibrate

Antenna’

In order to perform the antenna LC tank using direct command

Calibrate Antenna binary weighted tuning capacitors have to

be connected between the two coil terminals to the pins

TRIM1_3 to TRIM1_0 and TRIM2_3 to TRIM2_0.

During automatic procedure, started by sending the direct

command Calibrate Antenna, the AS3911 finds position of TRIM

switches at which the phase difference between the RFO output

signal and RFI input signal is as close as possible to target phase

defined in the Antenna Calibration Target Register.

In case the antenna LC tank is directly connected to RFO pins

(as in case of Figure 123) there is 90° phase shift between signal

on the RFO outputs and the voltage on the RFI inputs when

antenna LC tank is in resonance. In case additional EMC filter is

inserted between RFO outputs and antenna LC tank the phase

shift in case of resonance depends on additional phase shift

generated by EMC filter.

During execution of the direct command Calibrate Antenna the

AS3911 runs several phase measurements and changes

configuration of TRIM pins in order to find the best possible

setting. Due to this the format of the Antenna Calibration Target

Phase result.

The TRIM pin configuration which is result of the direct

command Calibrate Antenna can be observed by reading the

Antenna Calibration Display Register. This register also contains

an error flag which is set in case the tuning to target phase was

not possible.

After the execution of direct command Calibrate Antenna the

actual phase can be checked by sending direct command

Measure Phase.

AS3911 Datasheet(PDF) 136 Page - ams AG