Atmel ATA5283 - Manual (Page 5)

5
4598H–AUTO–03/07
ATA5283
3.4 Signal Conditioner
The signal conditioner demodulates the amplifier output signal and converts it to a binary signal.
It compares the carrier signal with the 50% reference level (see Ref1 in
Figure 3-3 ) and delivers
a logical 1, if the carrier signal stays below the reference and a logical 0, if it exceeds the refer-
ence level. A smoothing filter suppress the space between the half-waves as well as a few
missing periods in the carrier and glitches during the gaps.
The output signal of the signal conditioner is used as the internal data signal for the data output,
the wake-up logic and the preamble detection.
The timing of the demodulated data signal is delayed related to the signal at the transmitting
end. This delay is a function of the carrier frequency, the behavior of the smoothing filter and the
antenna Q-factor. The smoothing filter causes a delay of 3 to 6 periods (see t
b
and t
d
in Figure
3-3 ). The rest of the delay is caused by the build-up time of the antenna signal and is condi-
tioned on the Q-factor (see t
a
and t
c
in Figure 3-3 ).
Figure 3-3. Output Timing
The following diagrams show the delay of the data signal as a function of the antenna Q-factor.
Figure 3-4. Turn On Delay Time (t
ON
) versus Antenna Q-Factor
t
b
t
ON
t
d
t
a
50%
100%
Coil
input
Comparator
output
Ref.2
N_DATA
Ref.1
t
c
t
OFF
0 50 40 30 20 10
250
200
50
0
150
max.
min.
typ.
100
Q-factor
t on
(µs)
f
field
= 125 kHz