AS3909 datasheet(62/77 Pages) AMSCO

62 / 77 page

AS3909/AS3910 – 62

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

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

When the measured level is equal or lower than the

target level, actual state of the Calibrate Register is

copied in the Modulation Depth Display Register (#11).

Content of this register is used to define the AM

modulated level.

Note(s):After this calibration procedure is finished, the content

of Antenna driver non-modulated level definition register (#13)

should not be changed. Modification of this register content

will change the non-modulated amplitude and therefore the

ration be-tween 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.

AM Modulation Depth Definition Using Antenna

Driver AM Modulated Level Definition Register (#12)

When the bit 7 (am_s) of the Modulation Depth Definition

by writing the Antenna Driver AM Modulated Level Definition

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:

Write the non-modulated level in register #13 (usually

it is all 0 to have the lower possible output resistance)

Switch on the transmitter

After the settling time (10μs should be enough), send

the direct command Measure RF. Read result from the

A/D Converter Output Register (#0E)

Calculate the target modulated level from the target

modulation index and result from the previous point

In the following iterations content of the register #13 is

modified, the command Measure RF performed and

result compared to the target modulated level as long

as the result is not equal or close enough to the target

modulated level.

At the end the content of the register #13 which results

in the target modulated level is written in the Antenna

Driver AM Modulated Level Definition Register (#12) while

the register #13 is restored with the non-modulated

level definition value.

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