AS3909 datasheet(32/77 Pages) AMSCO

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AS3909/AS3910 – 32

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

Measure RF

This command measures the amplitude on the RFI inputs and

stores result in the A/D Converter Output Register (see also “A/D

Converter” on page 11 and “Amplitude Detector” on page 19).

When this command is executed the output of the Amplitude

detector is multiplexed to the A/D converter input (the A/D

converter is in absolute mode). The Amplitude Detector

conversion gain is 0.6 Vinpp/Vout. One LSB of the A/D converter

output represents 13.02mVpp on the RFI inputs, a 3Vpp signal

which is maximum allowed level on each of the two RFI inputs

results in 1.8V output DC voltage and would produce the value

of 1110 0110 on the A/D converter output.

Duration time: 42μs max.

This command is accepted in any mode where the oscillator and

regulators are running.

Squelch

This direct command is intended to avoid demodulation

problems of transponders which produce a lot of noise during

data processing (while data sent by reader is processed and

answer prepared). It can also be used in a noisy environment.

The operation of this command is explained in “Squelch” on

page 16.

Duration time: 500μs max

This command is only accepted when the Transmitter and

Receiver are operating.

Clear Squelch

Clears the gain reduction which was established by sending

Squelch command.

This command is accepted in any mode.

Adjust Regulators

When this command is sent the power supply level of VDD is

measured in maximum load conditions and the regulated

voltage reference is set 250 mV below this measured level to

assure maximum possible stable regulated supply (see “Power

Supply, Regulators” on page 21). Using this command increases

the system PSSR.

At the beginning of execution of this command, both the

receiver and transmitter are switched on to have the maximum

current consumption, the regulators are set to the maximum

3.4V regulated voltage. After 300μs VSP_RF is compared to VDD,

in case VSP_RF is not at least 250mV lower the regulator setting

is reduced for one step (100mV) and measurement is done after

300μs. Procedure is repeated as long as VSP_RF drops 250mV

below VDD of until minimum regulated voltage (2.4V) is

reached.

Duration time: 5ms max

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