TDA4884 Philips Semiconductors, TDA4884 Datasheet - Page 5

• Manufacturer Part Number: TDA4884
• Description: Advanced monitor video controller for OSD
• Manufacturer: Philips Semiconductors

Philips Semiconductors
6
7
The RGB input signals 0.7 V (p-p) are capacitively coupled
into the TDA4884 (pins 2, 5 and 8) from a low ohmic
source and are clamped to an internal DC voltage (artificial
black level). Composite signals will not disturb normal
operations because an internal clipping circuit cuts all
signal parts below black level. All channels have a
maximum total voltage gain of 7 dB (maximum contrast
and maximum individual channel gain). With the nominal
channel gain of 1 dB and nominal contrast setting the
nominal black-to-white output amplitude is 0.79 V (p-p).
DC voltages are used for contrast and gain control.
7.1
Contrast control is achieved by a voltage at pin 6 and
affects the three channels simultaneously. To provide the
correct white point, an individual gain control (pins 3, 1 and
11) adjusts the signals of channels 1, 2 and 3.
1997 Nov 26
GC2
VIN1
GC1
GND
VIN2
CC
V
VIN3
HBL
CL
GC3
FB3
VOUT3
IOUT3
FB2
VOUT2
IOUT2
FB1
VOUT1
IOUT1
SYMBOL
P
Three gain control video pre-amplifier for OSD
PINNING
FUNCTIONAL DESCRIPTION
Contrast control
PIN
10
12
13
14
15
16
17
18
19
20
11
1
2
3
4
5
6
7
8
9
gain control channel 2
signal input channel 1
gain control channel 1
ground
signal input channel 2
contrast control, OSD switch
supply voltage
signal input channel 3
horizontal blanking, switch-off
input clamping, vertical blanking,
test mode
gain control channel 3
feedback channel 3
voltage output channel 3
current output channel 3
feedback channel 2
voltage output channel 2
current output channel 2
feedback channel 1
voltage output channel 1
current output channel 1
DESCRIPTION
5
7.2
Each output stage provides a current output (pins 20, 17
and 14) and a voltage output (pins 19, 16 and 13). External
cascode transistors reduce power consumption of the IC
and prevent breakdown of the output transistors. Signal
output currents and peaking characteristics are
determined by external components at the voltage outputs
and the video supply. The channels have separate internal
feedback loops which ensure large signal linearity and
marginal signal distortion irrespective of output transistor
thermal V
7.3
The clamping pulse (pin 10) is used for input clamping
only. The input signals have to be at black level during the
clamping pulse and are clamped to an internal artificial
black level. The coupling capacitors are used in this way
for black-level storage. Because the threshold for the
clamping pulse is higher than that for vertical blanking
(pin 10) the rise and fall times of the clamping pulse need
handbook, halfpage
Output stages
Input clamping
BE
variation.
VIN1
GND
VIN2
VIN3
GC2
GC1
HBL
CC
V P
Fig.2 Pin configuration.
CL
10
1
2
3
4
5
6
7
8
9
TDA4884
MHA918
15
14
13
12
19
18
17
16
11
20
Product specification
IOUT1
VOUT1
FB1
IOUT2
VOUT2
FB2
VOUT3
IOUT3
FB3
GC3
TDA4884