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

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. = 50

µs,

see fig. 1). If the RF-signal is weak, the corner

NOTES TO THE CHZARACTERISTICS (continued)

4. ACI (ADJACENT CHANNEL INTERFERENCE)

α114 =

(signal)

α190 =

(signal)

measured with : 90% mono signal; 9% pilot signal; fm=1KHz; 1% spurious signal

6. MEASUREMENT OF TRIGGER THRESHOLDS

All thresholds are measured by using a pulse

The repetition rate must not increase the PEAK

voltage.

VTR

Vin

DC

TR

THIGH

TF

Time

D95AU365

-0.5

-0.4

-0.3

-0.2

-0.1

0

1

2

3.18

(=50

µs)

(KHz)

D95AU366

Figure 1: High Cut Control

-0.40

-0.32

-0.24

-0.16

0

10

20

30

40

50

SEP

(dB)

D95AU367

Figure 2: Stereo Blend

TDA7338

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