ML6421
FUNCTIONAL DESCRIPTION
APPLICATION GUIDELINES
The ML6421 single-chip Triple Video Filter IC is intended
for consumer and low cost professional video
applications. Each of the three channels incorporates an
input buffer amplifier, a sixth order lowpass filter, a first
order allpass equalizer, Sinx/x equalizer and an output
amplifier capable of driving 75Ω to ground.
OUTPUTCONSIDERATIONS
The triple filters have unity gain. The circuit has unity
gain (0dB) when connected to a 150Ω load, and a –6dB
gain when driving a 75Ω load via a 75Ω series output
resistor. The output may be either AC or DC coupled. For
AC coupling, the –3dB point should be 5Hz or less. There
must also be a DC path of -500Ω to ground for output
biasing.
The ML6421 can be driven by a DAC with Range down to
0V. When Range is low the input and output signal range
is 0.5V to 2.5V. When the input signal includes 0V, Range
should be tied high. In this case, an offset is added to the
input so that the output swing is kept between 0.5V to
2.5V. The output amplifier is capable of driving up to
24mA of peak current; therefore the output voltage should
not exceed 1.8V when driving 75Ω to ground.
INPUTCONSIDERATIONS
The input resistance is 4kΩ. The input may be either DC or
AC coupled. (Note that each input sources 80 to 125µA of
bias current). The ML6421 is designed to be directly
driven by a DAC. For current output video DACs, a 75Ω or
150Ω resistor to ground may need to be added to the DAC
output (filter input).
+5V
FB2
0.001µF
SUPPLY NOISE
CLAMPING
47Ω
0.1µF
100µF
47Ω
47Ω
0.1µF
1µF
3.1kΩ
INB
1µF
1µF
85Ω
100µF
INPUT
DECOUPLING
0.1µF
1
16
15
14
13
12
11
10
9
3.1kΩ
GNDB
V
B
A
IN
1kΩ
3.1kΩ
2
INC
V
IN
C
V
IN
100µF
1kΩ
DC
BIAS
INPUT SIGNAL = 2V
P-P
3
1kΩ
GND
RANGE
GNDA
GND
85Ω
0.1µF
INPUT
TERMINATION
4
5
6
7
8
1nF
1nF
GNDC
INA
FB1
0.1µF
0.1µF
85Ω
1nF
100µF
V
CC
0.1µF
V
CC
C
V
CC
A
OUTC
OUTA
OUTB
V
C
V
A
OUT
OUT
75Ω
75Ω
75Ω
1nF
V
CC
B
V
B
OUT
0.1µF
Figure 9. ML6421 AC Coupled DC Bias Test Circuit
8
MICRO-LINEAR [ MICRO LINEAR CORPORATION ]
