TDA7338 Datasheet, PDF (5/11 Pages) STMicroelectronics – STEREO DECODER

NOTES TO THE CHZARACTERISTICS (continued)
4. ACI (ADJACENT CHANNEL INTERFERENCE)
α114
=
V_O (signal) (at1KHz)
V_O (spurious) (at4KHZ)
;
fs
=
110KHz -
(3
x
38KHz)
α190
=
VO (signal) (at1KHz)
V_O (spurious) (at4KHZ)
;
fs
=
186KHz -
(5
x
38KHz)
measured with : 90% mono signal; 9% pilot signal; fm=1KHz; 1% spurious signal
(f_s = 110KHz or 186KHz, unmodulated)
5. Control range typ 11% of VR (see figure 1 and figure2)
6. MEASUREMENT OF TRIGGER THRESHOLDS
All thresholds are measured by using a pulse
with TR = 2µs, THIGH = 2µs, and TF = 10µs.
Vin
The repetition rate must not increase the PEAK
voltage.
VTR
DC
TDA7338
D95AU365
TR THIGH
TF
Time
FUNCTIONAL DESCRIPTION
Signal Path
The TDA7338 Stereodecoder contains all neces-
sary functions for processing the MPX signal. Due
to the external input resistance (Pin 20) the circuit
can be adapted to different MPX input levels. Be-
hind a 80kHz lowpass filter the adjustment free
PLL for the pilot Tone is placed. The only external
component needed for the PLL is the ceramic
Figure 1: High Cut Control
f_c
(KHz)
D95AU366
3.18
(=50µs)
2
VR=3.6V
resonator for the oscillator which runs at 456kHz.
The pilot detector output is designed as an open
collector output, therefore an external pullup re-
sistor is needed. To force the decoder to ”MONO”
Pin 19 has to be clamped to a voltage below
0.8V.
The voltage level (signal strength from the IF part)
applied to Pin 15 (VHCC) allows to control the
time constant of the deemphasis (nom. = 50µs,
see fig. 1). If the RF-signal is weak, the corner
Figure 2: Stereo Blend
SEP
(dB)
50
D95AU367
40
V_R=3.6V
30
1
0
-0.5 -0.4 -0.3 -0.2 -0.1 0.0 V_HCC-V_R(V)
20
10
0
-0.40
-0.32
-0.24
-0.16
-0.08 V_SB-V_R(V)
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