AS3909 데이터 시트보기 (PDF) - austriamicrosystems AG

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AS3909

13.56 MHz RFID Reader IC, ISO-14443 A/B

austriamicrosystems AG 

Application Information

The figure below depicts setting of the mod bits for some often

used modulation indexes.

Figure 50:

Setting mod bits for Modulation Indexes

modulation index [%]

8

10

14

20

30

33

a/b [dec]

1,1739

1,2222

1,3256

1,5000

1,8571

1,9843

a/b [bin]

1,001011

1,001110

1,010100

1,100000

1,110111

1,111111

mod5………mod0

001011

001110

010100

100000

110111

111111

Execution of Direct Command Calibrate Modulation Depth

The modulation level is adjusted by increasing the RFO1 and

RFO2 driver output resistance. The RFO drivers are composed

of 8 binary weighted segments. Usually all these segments are

turned on to define the normal, non-modulated level, there is

also a possibility to increase the output resistance of the

non-modulated state by writing the Antenna driver

non-modulated level definition register (#13).

Before sending the direct command Calibrate Modulation Depth

the oscillator and regulators have to be turned on. When the

direct command Calibrate Modulation Depth is sent the

following procedure is executed:

1. The Transmitter is turned on, non-modulated level is

established

2. The amplitude of the non-modulated carrier level

established on the inputs RFI1 and RFI2 is measured by

the A/D converter and stored in the A/D Converter

Output Register

3. Based on the measurement of the non-modulated level

and the target modulated level defined by the bits mod5

to mod0 the target modulated level is calculated

4. The output driver control is taken over by the eight bit

Calibrate Register with initial level defined in the

Antenna Driver Non-Modulated Level Definition Register

(#13). Content of the Calibrate Register is incremented

by 1 to increase the driver resistance, the reduced

amplitude is measured by the A/D converter and the

result is compared to the target modulation level.

5. The procedure from previous point is repeated as long

as the measured level is greater than target level.

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

AS3909/AS3910 – 61

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