ML6426
FUNCTIONAL DESCRIPTION
The ML6426 is a triple monolithic continuous time video
filter designed for reconstructing video signals from an
YUV/RGB video D/A source. The ML6426 is intended for
use in AC coupled input and output applications.
The filters approximate a 4th-order Butterworth
characteristic with an optimization toward low overshoot
and flat group delay. All outputs are capable of driving
2V
P-P
into AC coupled 150W video loads, with up to 35pF
of load capacitance. All outputs are capable of driving a
75W load at 1V
P-P
.
All channels are clamped during sync to establish the
appropriate output voltage swing range (DC restore). Thus
the input coupling capacitors do not behave according to
the conventional RC time constant. In most applications,
the ML6426's input coupling capacitors are only 0.1µF.
An external CMOS compatible H
SYNC
pulse is required
which is Active High on the SYNC IN Pin. See Figure 2.
During sync, the feedback clamp sources/sinks current to
restore the DC level. The net result is that the average
input current is zero. Any change in the input coupling
capacitors' value will linearly affect the clamp response
times.
Each channel is essentially tilt-free. Each input is
clamped by a feedback amp which responds to the output
during sync.
The ML6426 is robust and stable under all stated load and
input conditions. Bypassing both V
CC
pins directly to
ground ensures this performance.
5V
12
VCCO
RINA/YINA
RINB/YINB
GINA/UINA
GINB/UINB
BINA/VINA
BINB/VINB
MUX
TRANSCONDUCTANCE
ERROR AMP
A/B MUX
1
SYNCIN
SYNC IN
16
ACTIVE HIGH
DISABLE
15
+
–
5V
4
VCC
220µF 75Ω
13
0.1µF
RIN
2
5
6
7
8
9
MUX
TRANSCONDUCTANCE
ERROR AMP
MUX
TRANSCONDUCTANCE
ERROR AMP
+
–
+
–
4th-ORDER
FILTER A
0.5V
4th-ORDER
FILTER B
0.5V
4th-ORDER
FILTER C
0.5V
×2
ROUT/YOUT
R
0.1µF
GIN
×2
GOUT/UOUT
220µF 75Ω
11
G
0.1µF
BIN
×2
BOUT/VOUT
220µF 75Ω
10
B
GNDO
14
GND
3
Figure 1. Typical Application Schematic
VIH = 2.5V
VIL = 1.0V
50% x VSYNC IN
PWMIN = 2µS
Figure 2. SYNC IN Pulse Width
6
November, 1999
MICRO-LINEAR [ MICRO LINEAR CORPORATION ]
