AS3911 datasheet(31/149 Pages) AMSCO

31 / 149 page

ams Datasheet, Confidential: 2013-Oct [2-03]

AS3911 – 31

Appl icatio n I n f o rm a t i o n

The General Purpose Timer can also be started by sending the

direct command Start General Purpose Timer. In case this

command is sent while the timer is running, it is reset and

restarted.

Wake-up Timer

Wake timer is primarily used in the Wake-up mode (see

“Wake-up Mode” on page 26). Additionally it can be used by

sending a direct command Start Wake-up Timer. This command

is accepted in any operation mode except Wake-up mode.

When this command is send the RC oscillator, which is used as

clock source for wake-up timer is started, timeout is defined by

setting in the Wake-up Timer Control Register. When the timer

expires, an IRQ with the I_wt flag in the Error and Wake-up

Interrupt Register is sent.

Wake-up timer is useful in the Power-down mode, in which

other timers cannot be used (in the Power-down mode the

crystal oscillator, which is clock source for the other timers, is

not running). Please note that the tolerance of wake-up timer

timeout is defined by tolerance of the RC oscillator.

A/D Converter

The AS3911 contains an 8-bit successive approximation A/D

converter. Input to A/D converter can be multiplexed from

different sources to be used in several direct commands and

adjustment procedures. The result of last A/D conversion is

stored in the A/D Converter Output Register. Typical conversion

time is 224/fc (16.5 μs).

The A/D converter has two operating modes, absolute and

relative.

• In absolute mode the low reference is 0V and the high

reference is 2V. This means that A/D converter input range

is from 0 to 2V, 00h code means input is 0V or lower, FFh

means that input is 2V - 1LSB or higher, LSB is 7.8125 mV.

• In relative mode low reference is 1/6 of VSP_A and high

reference is 5/6 of VSP_A, so the input range is from 1/6

VSP_A to 5/6 VSP_A.

Relative mode is only used in phase measurement (phase

detector output is proportional to power supply). In all other

cases absolute mode is used.

Phase and Amplitude Detector

This block is used to provide input to A/D Converter to perform

measurements of amplitude and phase, expected by direct

commands Measure Amplitude and Measure Phase. Several

phase and amplitude measurements are also performed by

direct commands Calibrate Modulation Depth and Calibrate

Antenna.

AS3911 Datasheet(PDF) 31 Page - ams AG

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