AS3911 datasheet(32/149 Pages) AMSCO

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AS3911 – 32

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

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

Phase Detector

The phase detector is observing phase difference between the

transmitter output signals (RFO1 and RFO2) and the receiver

input signals RFI1 and RFI2, which are proportional to the signal

on the antenna LC tank. These signals are first passed by

digitizing comparators. Digitized signals are processed by a

phase detector with a strong low pass filter characteristics to

get average phase difference. The Phase Detector output is

inversely proportional to the phase difference between the two

inputs. The 90° phase shift results in VSP_A/2 output voltage,

in case both inputs are in phase output voltage is VSP_A in case

they are in opposite phase output voltage is zero. During

execution of direct command Measure Phase this output is

multiplexed to A/D Converter input (A/D Converter is in relative

mode during execution of command Measure Phase). Since the

A/D converter range is from 1/6 VSP_A to 5/6 VSP_A the actual

phase detector range is from 30º to 150º. Figures below depict

the two inputs and output of phase detector in case of 90º and

135º phase shift.

Figure 17:

Phase Detector Inputs and Output in case of 90º Phase Shift

VSP

VSP/2

AS3911 Datasheet(PDF) 32 Page - ams AG