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[v2-11] 2016-Jun-13

AS3911 − Application Information

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 RFO Normal Level

Definition Register.

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:

• The Transmitter is turned on, non-modulated level is

established.

• 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

• 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.

• The output driver control is taken over by the Calibrate

successive approximation algorithm as long as long as the

measured level is equal or as close as possible to target

modulated level calculated in previous step.

• Final state of the Calibrate Register is copied in the AM

Modulation Depth Display Register. Content of this

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

of the RFO Normal Level Definition Register should not be

changed. Modification of this register content will change the

non-modulated amplitude and therefore the ratio between the

modulated and non-modulated level will be changed. Please

also note that in case the calibration of antenna resonant

frequency in used, command Calibrate Antenna has to be run

before AM modulation depth adjustment.

AM Modulation Depth Definition Using the ‘RFO AM

Modulated Level Definition’ Register

When the bit 7 (am_s) of the AM Modulation Depth Control

writing the RFO AM Modulated Level Definition Register. 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.

It is also possible to implement calibration procedure in

external controller using the RFO Normal Level Definition

procedure has to be used in case the target modulation depth

is deeper than 33%.

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