Philips TDA8303A - Manual (Page 2)

July 1992 2
Philips Semiconductors Preliminary specification
Small signal combination IC for black/white TV
TDA8303
TDA8303A
FEATURES
•
Video IF amplifier with synchronous demodulator
•
Automatic gain control (AGC) detector suitable for
negative modulation
•
AGC tuner
•
Automatic frequency control (AFC) circuit with
sample-and-hold
•
Video preamplifier
•
Sound IF amplifier and demodulator
•
DC volume control or separate supply for starting the
horizontal oscillator
•
Audio preamplifier
•
Horizontal synchronization circuit with two control loops
•
Vertical synchronization (divider system) and sawtooth
generation with automatic amplitude adjustment for 50
and 60 Hz
•
Transmitter identification (mute)
GENERAL DESCRIPTION
The TDA8303/TDA8303A combines all small signal
functions (except the tuner) which are required for a
monochrome television receiver. For a complete black and
white receiver only the output stages for video, sound,
horizontal and vertical deflection and a tuner have to be
added.
The TDA8303 is for applications with npn tuners and the
TDA8303A for pnp tuners.
FUNCTIONAL DESCRIPTION
Video IF amplifier, demodulator and video amplifier
Each of the three AC-coupled IF stages permits the
omission of DC feedback and possesses a control range
in excess of 20 dB. An additional advantage is the
symmetry of the amplifier which results in a less critical
application.
The IF amplifier is followed by a passive synchronous
demodulator providing a regenerated carrier signal. This is
limited by a logarithmic limiter circuit prior to its application
to the demodulator. The limiter has a very low differential
phase shift which results in good differential gain and
phase figures.
The video amplifier also contains a white spot inverter and
a noise clamp which limits interference pulses to a point
below the peak sync level. This circuit is more effective
than a noise inverter and results in an improved picture
stability, with respect to interference.
AFC-circuit
The reference signal for the AFC circuit is obtained from
the demodulator tuned circuit. In this way only one tuned
circuit needs to be applied and only one adjustment has to
be carried out. The disadvantage with this method is that
the frequency spectrum of the signal fed to the detector is
determined by the SAW filter characteristic. This spectrum
is asymmetrical with respect to the picture carrier so that
the AFC output voltage is dependent on the video signal.
To overcome this video frequency dependency of the AFC
output, the demodulator output is followed by a
sample-and-hold circuit which samples during the sync
level of the signal. This means that only the carrier signal
is available to the AFC and it will not be affected by the
video information.
At very weak input signals the drive signal of the AFC
circuit will contain substantial noise. This noise has an
asymmetrical frequency spectrum causing an offset in the
AFC output voltage. This effect can be minimized by
applying a notch in the demodulator tuned circuit. The
sample-and-hold circuit is followed by an amplifier with
high output impedance, therefore the steepness of the of
the AFC control voltage is dependent on the load
impedance.
ORDERING INFORMATION
Note
1. SOT117-1; 1996 December 3.
EXTENDED TYPE
NUMBER
PACKAGE
PINS PIN POSITION MATERIAL CODE
TDA8303 28 DIL plastic SOT117 (1)
TDA8303A 28 DIL plastic SOT117 (1)