Philips TDA3857 Datasheet
INTEGRATED CIRCUITS
DATA SH EET
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
TDA3857
FM demodulators
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
I
P
V
i IF
V
o AF
THD total harmonic distortion − 0.5 − %
S/N (W) weighted signal-to-noise ratio − 68 − dB
ORDERING INFORMATION
EXTENDED
TYPE NUMBER
TDA3857 20 DIL plastic SOT146
Note
1. SOT 146-1; 1996 November 28.
supply voltage (pin 19) 4.5 5 8.8 V
supply current − 60 72 mA
IF input sensitivity (−3 dB) − 70 100 µV
audio output signal (RMS value) − 1 − V
PACKAGE
PINS
PIN
POSITION
MATERIAL CODE
(1)
June 1994 2
Philips Semiconductors Product specification
Quasi-split sound processor with two FM demodulators TDA3857
Fig.1 Block diagram (standard B/G).
June 1994 3
Philips Semiconductors Product specification
Quasi-split sound processor with two FM demodulators TDA3857
PINNING
SYMBOL PIN DESCRIPTION
FMIF1 1 IF difference input 1 for B/G standard (38.9 MHz)
C
AGC
MATR 3 input for stereo matrix correction
FM2R1 4 reference circuit for FM2 (5.74 MHz)
FM2R2 5 reference circuit for FM2 (5.74 MHz)
AF2 6 AF2 output (AF out of 5.74 MHz)
AF1 7 AF1 output (AF out of 5.5 MHz)
FM1R1 8 reference circuit for FM1 (5.5 MHz)
FM1R2 9 reference circuit for FM1 (5.5 MHz)
VC-R1 10 reference circuit for the vision carrier (38.9 MHz)
VC-R2 11 reference circuit for the vision carrier (38.9 MHz)
TRACK 12 DC output level for tracking
FM1I 13 intercarrier input for FM1 (5.5 MHz)
C
AF1
ICO 15 intercarrier output signal (5.5/5.74 MHz)
C
AF2
FM2I 17 intercarrier input for FM2 (5.74 MHz)
GND 18 ground (0 V)
V
P
FMIF2 20 IF difference input 2 for B/G standard (38.9 MHz)
2 charge capacitor for AGC
14 DC decoupling capacitor for FM1 demodulator
(AF1)
16 DC decoupling capacitor for FM2 demodulator
(AF2)
19 +5 to +8 V supply voltage
Fig.2 Pin configuration.
June 1994 4
Philips Semiconductors Product specification
Quasi-split sound processor with two FM demodulators TDA3857
FUNCTIONAL DESCRIPTION
The quasi-split sound processor is suitable for all FM
standards (e. g. B/G).
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.
Muting
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.
Sound carrier notch filter for an improved intercarrier
buzz
The series capacitor C
in the 38.9 MHz resonant circuit
s
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
has to be adapted to other TV transmission standards if
necessary, according to the formula
C
Cpfvcfsc⁄()
s
2
C
–=
p
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.
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.
Measurements at the demodulators
For all signal-to-noise measurements the generator must
meet the following specifications:
phase modulation errors < 0.5°for B/W-jumps intercarrier
signal-to-noise ratio as measured with ‘TV-demodulator
AMF2’ (weighted S/N) must be > 60 dB at 6 kHz sine
wave modulation of the B/W-signal.
Signal-to-noise ratios are measured with ∆f=±50 kHz
deviation and f
= 1 kHz; with a deviation of ±30 kHz the
mod
S/N ratio is deteriorated by 4.5 dB.
June 1994 5
Loading...