TDA4672 Datasheet, PDF (5/16 Pages) NXP Semiconductors – Picture Signal Improvement PSI circuit with enhanced peaking function

Philips Semiconductors
Picture Signal Improvement (PSI) circuit
with enhanced peaking function
Product specification
TDA4672
FUNCTIONAL DESCRIPTION
The TDA4672 contains luminance signal processing.
The luminance signal section comprises a variable,
integrated luminance delay line with luminance signal
peaking and noise reduction by coring.
All functions and parameters are controlled via the
I²C-bus.
Y-signal path
The video and blanking signal is AC-coupled to the input
pin 16. Its black porch is clamped to a DC reference
voltage to ensure the correct operating range of the
luminance delay stage.
The luminance delay line consists of all-pass filter sections
with delay times of 45, 90, 100, 180 and 450 ns
(see Fig.1). The luminance signal delay is controlled via
the I²C-bus in steps of 45 ns in the range of 20 to 1100 ns,
this ensures that the maximum delay difference between
the luminance and colour-difference signals is ±22.5 ns.
An automatic luminance delay time adjustment in an
internal control loop (with the horizontal frequency as a
reference) is used to correct changes in the delay time,
due to component tolerances. The control loop is
automatically enabled between the burst key pulses of
lines 16 (330) and 17 (331) during the vertical blanking
interval. The control voltage is stored in the capacitor C_DL
connected to pin 2.
The peaking section uses a transversal filter circuit with
selectable centre frequencies of 2.6 and 5.0 MHz.
It provides selectable degrees of peaking from −6 to +9 dB
and noise reduction by coring, which attenuates the
high-frequency noise introduced by peaking.
The output buffer stage ensures a low-ohmic Video
Blanking Synchronization (VBS) output signal on pin 12
(<160 Ω). The gain of the luminance signal path from
pin 16 to pin 12 is unity.
An oscillation signal of the delay time control loop is
present on output pin 12 instead of the VBS signal. It is
present during the vertical blanking interval of the burst key
pulses in lines 16 (330) to 18 (332). This sync should not
be applied for synchronization.
Colour-difference signal paths
The colour-difference input signals (on pins 3 and 7) are
connected directly to the output pins.
This is for compatibility with other Philips Semiconductors
PSI-circuits.
1996 Dec 11
5