CAP 3001 A
dB
3
gain
0
*3
0.0
5.0
10.0
15.0
f
20.0
22.05 kHz
Fig. 2–10: Digital interpolation filter, passband characteristic
dB
0
gain
*50
*80
0.0
50
100
150
200
250
300
350 kHz
f
Fig. 2–11: Digital interpolation filter, attenuation
2.1.13.2. ARI Mixer ARIMX
lated ARI signal would be identical with the signal of the
inphase path.
The ARI-information in the range of 57 kHz is mixed
down to a zero intermediate frequency by the two ARI
mixers, whose mixer signals are again in quadrature.
The reason for using two paths is that the demodulation
is asynchronous in general; in the DSP there should be
an operation which performs the square root of the sum
of the squares of the two input signals. The quality re-
quirements of the square rooting should not be very
high. Because of the phase lock of pilot tone and ARI
carrier in the FM-stereo-mode, a synchronous demodu-
lation seems to be possible; in this case the demodu-
The chosen structure has another potential advantage,
for processing the radio data system (RDS) in Europe.
This signal is a part of the MPX-signal; its subcarrier fre-
quency is the same as that of the ARI-signal but it is rec-
ommended that the two subcarriers are in quadrature.
So the two paths of the ARI demodulation subsystem
make the information of the ARI-signal and of the RDS-
signal available to the DSP, where both can be demodu-
lated if desired.
MICRONAS INTERMETALL
11
MICRONAS [ MICRONAS ]
