TDA3857.PDF

INTEGRATED CIRCUITS

DATA SHEET

TDA3857

Quasi-split sound processor with

two FM demodulators

Product speciﬁcation

File under Integrated Circuits, IC02

June 1994

Philips Semiconductors

Product speciﬁcation

Quasi-split sound processor with two

FM demodulators

TDA3857

FEATURES

Quasi-split sound processor for all FM standards e. g. B/G

Reducing of spurious video signals by tracking function and AFC for the vision carrier reference circuit; (recommended

for NICAM)

Automatic muting of the AF2 signal by the input level

Stereo matrix correction

Layout-compatible with TDA3856 (24 pins) and TDA3858 (32 pins).

GENERAL DESCRIPTION

Symmetrical IF inputs. Gain controlled wideband IF amplifier.

AGC generation due to peak sync. Reference amplifier for the regeneration of the vision carrier. Optimized limiting

amplifier for AM suppression in the regenerated vision carrier signal and 90

phase shifter.

Intercarrier mixer for FM sound, output with low-pass filter.

Separate signal processing for 5.5 and 5.74 MHz intercarriers. Wide supply voltage range, only 300 mW power

dissipation at 5 V.

QUICK REFERENCE DATA

SYMBOL

PARAMETER

MIN. TYP. MAX. UNIT

V P

supply voltage (pin 19)

4.5

8.8

I P

supply current

V i IF

IF input sensitivity (

3 dB)

100

V o AF

audio output signal (RMS value)

THD

total harmonic distortion

0.5

S/N (W)

weighted signal-to-noise ratio

ORDERING INFORMATION

PACKAGE

EXTENDED

TYPE NUMBER

PINS

POSITION

MATERIAL

CODE

TDA3857

DIL

plastic

SOT146 (1)

Note

1. SOT 146-1; 1996 November 28.

June 1994

Philips Semiconductors

Product speciﬁcation

Quasi-split sound processor with two FM demodulators

TDA3857

Fig.1 Block diagram (standard B/G).

June 1994

Philips Semiconductors

Product speciﬁcation

Quasi-split sound processor with two FM demodulators

TDA3857

PINNING

SYMBOL

DESCRIPTION

FMIF1

IF difference input 1 for B/G standard (38.9 MHz)

C AGC

charge capacitor for AGC

MATR

input for stereo matrix correction

FM2R1

reference circuit for FM2 (5.74 MHz)

FM2R2

reference circuit for FM2 (5.74 MHz)

AF2

AF2 output (AF out of 5.74 MHz)

AF1

AF1 output (AF out of 5.5 MHz)

FM1R1

reference circuit for FM1 (5.5 MHz)

FM1R2

reference circuit for FM1 (5.5 MHz)

VC-R1

reference circuit for the vision carrier (38.9 MHz)

VC-R2

reference circuit for the vision carrier (38.9 MHz)

TRACK

DC output level for tracking

FM1I

intercarrier input for FM1 (5.5 MHz)

C AF1

DC decoupling capacitor for FM1 demodulator

(AF1)

ICO

intercarrier output signal (5.5/5.74 MHz)

C AF2

DC decoupling capacitor for FM2 demodulator

(AF2)

FM2I

intercarrier input for FM2 (5.74 MHz)

GND

ground (0 V)

V P

+5 to +8 V supply voltage

Fig.2 Pin configuration.

FMIF2

IF difference input 2 for B/G standard (38.9 MHz)

June 1994

Philips Semiconductors

Product speciﬁcation

Quasi-split sound processor with two FM demodulators

TDA3857

FUNCTIONAL DESCRIPTION

has to be adapted to other TV transmission standards if

necessary, according to the formula

The quasi-split sound processor is suitable for all FM

standards (e. g. B/G).

C s

C p

(

f vc

f sc

)

–

C p

B/G standard

AGC detector uses peak sync level. Sound carrier SC1

(5.5 MHz) provides AF1, sound carrier SC2 (5.74 MHz)

provides AF2.

The result is an improved intercarrier buzz (up to 10 dB

improvement in sound channel 2 with 250 kHz video

modulation for B/G stereo) or suppression of 350 kHz

video modulated beat frequency in the digitally-modulated

NICAM subcarrier.

Muting

Intercarrier buzz ﬁne tuning with 250 kHz square

wave video modulation

The picture carrier for quadrature demodulation in the

intercarrier mixer is not exactly 90 degrees due to the shift

variation in the integrated phase shift network. The tuning

of the LC reference circuit to provide optimal video

suppression at the intercarrier output is not the same as

that to provide optimal intercarrier buzz suppression. In

order to optimize the AF signal performance, a fine tuning

for the optimal S/N at the sound channel 2 (from 5.74 MHz)

may be performed with a 250 kHz square wave video

modulation.

With no sound carrier SC2 at pin 17, AF2 output is muted.

The mute circuit prevents false signal recognition in the

stereo decoder at high IF signal levels when no second

sound carrier exists (mono) and an AF signal is present in

the identification signal frequency range.

With 1 mV at pin 17, under measurement conditions, AF2

is switched on (see limiting amplifier). Weak input signals

at pins 1 and 20 generate noise at pin 17, which is present

in the intercarrier signal and passes through the 5.74 MHz

filter. Noise at pin 17 inhibits muting. No misinterpretation

due to white noise occurs in the stereo decoder, when

non-correlated noise masks the identification signal

frequencies, which may be present in sustained tone

signals. The stereo decoder remains switched to mono.

Measurements at the demodulators

For all signal-to-noise measurements the generator must

meet the following specifications:

phase modulation errors

Sound carrier notch ﬁlter for an improved intercarrier

buzz

for B/W-jumps intercarrier

signal-to-noise ratio as measured with ‘TV-demodulator

AMF2’ (weighted S/N) must be

0.5

The series capacitor C s in the 38.9 MHz resonant circuit

provides a notch at the sound carrier frequency in order to

provide more attenuation for the sound carrier in the vision

carrier reference channel. The ratio of parallel/series

capacitor depends on the ratio of VC/SC frequency and

60 dB at 6 kHz sine

wave modulation of the B/W-signal.

Signal-to-noise ratios are measured with

50 kHz

deviation and f mod = 1 kHz; with a deviation of

30 kHz the

S/N ratio is deteriorated by 4.5 dB.

June 1994

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