AS3909 datasheet(63/77 Pages) AMSCO

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ams Datasheet, Confidential: 2013-Oct [3-02]

AS3909/AS3910 – 63

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

Antenna LC Tank Resonance: Checking and

Calibration

The AS3909/10 comprises the building blocks which make

possible checking and adjustment of the antenna LC tank

resonance frequency. The arrangement of these building blocks

and associated adjustment procedure are patent pending.

The key block in the resonance frequency checking and

adjustment is the Phase Detector (see “Phase Detector” on

page 18). The Phase Detector is measuring the phase shift

between the Transmitter output signals (RFO1 and RFO2) and

the inputs RFI1 and RFI2, which are proportional to voltage on

the antenna LC tank. In case of perfect tuning there is a 90º

phase shift between them.

Check Antenna Resonance

In case of the perfect 90º phase shift mentioned above, the

Phase Detector output results in VSP/2 output voltage. A phase

shift of 1% of the carrier frequency period (3.6º) results in the

output voltage change of 2% of VSP (1% phase shift results in

60mV change at VSP=3V).

During execution of the direct command Check Antenna

Resonance the Phase Detector output is multiplexed on the

input of A/ D converter which is set in relative mode. 1 LSB of

the A/D conversion output represents 0.13% of carrier

frequency period (0.468º). The result of A/D conversion is in case

of the perfect tuning exactly in the middle of range (1000 0000

or 0111 1111).

Value higher than 1000 0000 means that phase detector output

voltage is higher than VSP/2, which corresponds to case with

resonance frequency higher than target 13.56 MHz. In the

opposite case, when the resonance frequency is lower than

target, the result of A/D conversion is lower than 0111 1111.

Execution of the command Check Antenna Resonance is fast and

it can be used frequently to check whether system settings are

correct.

AS3909 数据表(PDF) 63 Page - ams AG

AS3909 数据表(HTML) 63 Page - ams AG

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