TDA9176 Philips Semiconductors, TDA9176 Datasheet - Page 5

• Manufacturer Part Number: TDA9176
• Description: Luminance Transient Improvement LTI IC
• Manufacturer: Philips Semiconductors

Philips Semiconductors
FUNCTIONAL DESCRIPTION
The TDA9176 is a Luminance Transient Improvement
(LTI) IC which is suitable for operation in both
50 and 100 Hz environments. The IC also contains
chrominance delay lines to compensate for the luminance
delay. A diagram of the LTI processor is illustrated in Fig.3.
The LTI processor contains a delay line which drives a
minimum/maximum (MINMAX) detector and a control
circuit. When the control circuit discovers a transient, the
LTI shaper switches from the minimum to the maximum
signal (or vice-versa, depending on the sign of the
transient). By mixing the original signal with the switched
signal, a variable transient improvement is obtained.
The 50% crossing point of the transient is not affected by
the LTI circuit.
If the rise time improvement is active, the duty cycle of the
output signal can be varied with the line width control input.
This function delays the rising edge and advances the
falling edge (or vice-versa). This can be used for example
aperture correction. Figures 4 and 5 illustrate some
waveforms of the LTI processor.
For correct operation the LTI circuit requires a number of
fast clamps. To overcome problems where noise is
superimposed on the input signal the device contains an
input clamp that can either clamp to the black level of the
input signal, or, insert a black level. When a black level is
inserted, the internal clamps do not respond to the noise
on the input signal (see Fig.1). When the input signal
already has an inserted black level (e.g. when it is driven
from the TDA9170 picture booster) it is recommended to
1996 Jan 30
handbook, full pagewidth
Luminance Transient Improvement (LTI) IC
YIN
4
DELAY
TDA9176
Fig.3 Block diagram of the LTI circuit.
CLAMPS
5
set the device to the clamping mode. If no inserted black
level is available on the input signal it is recommended to
select the black insert mode of the input clamp.
The chrominance delay lines compensate for the delay of
the luminance signal in the LTI circuit. This is to safeguard
a correct colour fit.
Two and three level sandcastles can be used as a timing
signal, only the clamp pulse of the sandcastle input is used
in the device.
There are three selection inputs to select the modes of
operation. These selections are as follows:
1. 1FH or 2FH, for the 50 or 100 Hz applications.
2. Amplitude selection, for optimum operation of the
3. Black insertion or clamping of the luminance signal.
The selection inputs must be directly connected to either
ground or the supply rail. The modes are selected as
follows:
If the selection pins are left floating, internal 1 M resistors
connected to the pins set the device to, 1FH mode, black
insert mode and 1 V
Frequency selection: GND = 1FH mode,
V
Amplitude selection: GND = 450 mV (p-p),
V
Black insertion/clamp: GND = clamp mode,
V
CC
CC
CC
circuit with 450 mV (p-p) or 1 V
CONTROL
MINMAX
= 2FH mode
= 1 V
= black insert mode.
LTI
bl-wh
mode
3
bl-wh
SHAPER
RT LW
LTI
mode.
MBE777
2
13
Preliminary specification
bl-wh
YOUT
luminance signals.
TDA9176