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ML6423CS-1

Dual S-Video Lowpass Filter with Phase and Sinx/x Equalization

Micro Linear Corporation 

ML6423

FUNCTIONAL DESCRIPTION

The ML6423 single-chip dual video filter is intended for

low cost professional and consumer video applications.

Each of the two channels incorporates an input buffer

amplifier, a 6th-order lowpass filter, a 1st-order allpass

equalizer, sinx/x equalizer and an output 2X gain

amplifier capable of driving 75W to ground. A third

output (B) is the sum of the A and C inputs and have the

identical output amplifier as the A and C channels.

The ML6423 can be driven by a DAC with RANGE down

to 0V. When RANGE is low the input range is 0.5V to

1.5V. When the input signal range is 0V to 0.1V, 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 75W to ground.

APPLICATION GUIDELINES

OUTPUT & INPUT CONSIDERATIONS

The dual filters have 2X gain. The circuit has 2X gain

(6dB) when connected to a 150W load, and 0dB gain

when driving a 75W load via a 75W 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 £500W to ground for output

biasing. The ML6423-5 provides higher sink current to

better drive AC coupled loads.

The input resistance is 4kW. The input may be either DC

or AC coupled. (Note that each input sources 80 to 125µA

of bias current). The ML6423 is designed to be directly

driven by a DAC. For current output video DACs, a 75W

or 150W resistor to ground may need to be added to the

DAC output (filter input).

+5V

+

FB2

0.1µF 1nF 100µF

SUPPLY NOISE

CLAMPING

100Ω

INPUT

DECOUPLING

0.1µF

VINC

INPUT SIGNAL

= 1VP-P

85Ω

+

100µF

DC

BIAS

INPUT

TERMINATION

RESISTOR

FB1

1µF

2.56kΩ

1kΩ

1 VINC

2 GND

1nF 3 GNDC

0.1µF

4

VCC

VOUTC

75Ω

VOUTB

75Ω

5 NC

6 VOUTC

0.1µF 7 VCCC

1nF

8 VOUTB

100Ω

2.56kΩ

1µF

100µF

+

VINA 16

1k

RANGE 15

GNDA 14 0.1µF

13

1nF

VCCA

0.1µF

VINA

85Ω

VOUTA 12

NC 11

VOUTA

75Ω

VCCB 10 0.1µF

GNDB 9

1nF

Figure 4. ML6423 AC Coupled DC Bias Test Circuit

6

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