AS3910-BQFP AMSCO [austriamicrosystems AG], AS3910-BQFP Datasheet - Page 41

• Manufacturer Part Number: AS3910-BQFP
• Description: 13.56 MHz RFID Reader IC, ISO-14443 A/B
• Manufacturer: AMSCO [austriamicrosystems AG]

AS3910
Data Sheet - A p p l i c a t i o n I n f o r m a t i o n
Execution of Direct Command Calibrate Modulation Depth.
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:
Note: After this calibration procedure is finished, the content of Antenna driver non-modulated level definition register (#13) should not be
8.15.2 AM Modulation Depth Definition Using Antenna Driver AM Modulated Level Definition Register (#12)
When the bit 7 (am_s) of the Modulation Depth Definition Register (#10) is set to 1 the AM modulated level is controlled by writing the Antenna
Driver AM Modulated Level Definition Register (#12). In case setting of the modulated level is already known it is not necessary to run the
calibration procedure, the modulated level can simply be defined by writing this register.
There is also a possibility to run a calibration procedure from externally using the Antenna driver non-modulated level definition register (#13)
and the direct command Measure RF. The procedure is the following:
8.16 Antenna LC Tank Resonance: Checking and Calibration
The AS3910 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
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.
www.austriamicrosystems.com/HF_RFID_Reader/AS3910
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
3. Based on the measurement of the non-modulated level and the target modulated level defined by the bits mod5 to mod0 the target
4. The output driver control is taken over by the eight bit Calibrate Register with initial level defined in the Antenna Driver Non-Modulated
5. The procedure from previous point is repeated as long as the measured level is greater then target level.
6. When the measured level is equal or lower than the target level, actual state of the Calibrate Register is copied in the Modulation Depth
1. Write the non-modulated level in register #13 (usually it is all 0 to have the lower possible output resistance)
2. Switch on the transmitter
3. After the settling time (10µs should be enough), send the direct command Measure RF. Read result from the A/D Converter Output
4. Calculate the target modulated level from the target modulation index and result from the previous point
5. In the following iterations content of the register #13 is modified, the command Measure RF performed and result compared to the tar-
6. At the end the content of the register #13 which results in the target modulated level is written in the Antenna Driver AM Modulated
changed. Modification of this register content will change the non-modulated amplitude and therefore the ration between the modulated
and non-modulated level will be changed.
Please also note that in case the Calibration of antenna resonant frequency in implemented command Calibrate Antenna has to be run
before AM modulation depth adjustment.
in the A/D Converter Output Register
modulated level is calculated
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.
Display Register (#11). Content of this register is used to define the AM modulated level.
Register (#0E)
get modulated level as long as the result is not equal or close enough to the target modulated level.
Level Definition Register (#12) while the register #13 is restored with the non-modulated level definition value.
Revision 2.3
The modulation level is adjusted by increasing the RFO1 and RFO2
(see Phase Detector on page
15). The Phase
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