ML6421

8

FUNCTIONAL DESCRIPTION

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 75

Ω to ground.

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 75

Ω to ground.

APPLICATION GUIDELINES

OUTPUT CONSIDERATIONS

The triple filters have unity gain. The circuit has unity

gain (0dB) when connected to a 150

Ω load, and a –6dB

gain when driving a 75

Ω 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 -500

Ω to ground for output

biasing.

INPUT CONSIDERATIONS

The input resistance is 4k

Ω. 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 75

Ω or

150

Ω resistor to ground may need to be added to the DAC

output (filter input).

Figure 9. ML6421 AC Coupled DC Bias Test Circuit

1

2

3

4

5

6

7

8

16

15

14

13

12

11

10

9

RANGE

GNDA

GND

GNDB

GND

GNDC

75

Ω

75

Ω

OUTA

OUTB

1

µF

0.1

µF

0.1

µF

100

µF

100

µF

3.1k

Ω

47

Ω

1k

Ω

85

Ω

47

Ω

85

Ω

3.1k

Ω

1k

Ω

INB

INA

0.1

µF

100

µF

1nF

1nF

1nF

1nF

0.1

µF

0.1

µF

0.1

µF

0.1

µF

0.1

µF

0.001

µF

1

µF

100

µF

75

Ω

85

Ω

47

Ω

OUTC

3.1k

Ω

1k

Ω

INC

+5V

FB2

FB1

DC

BIAS

INPUT

DECOUPLING

SUPPLY NOISE

CLAMPING

INPUT

TERMINATION

1

µF