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MAX9517

Standard-Definition Video Filter Amplifiers with Dual SPST Switches

Maxim Integrated 

Standard-Definition Video Filter Amplifiers with

Dual SPST Switches

AC-Coupling the Outputs

The outputs can be AC-coupled because the output

stage can source and sink current as shown in Figure 1.

Coupling capacitors should be 220µF or greater to keep

the highpass filter formed by the 150Ω equivalent resis-

tance of the video transmission line to a corner frequen-

cy of 4.8Hz or below. The frame rate of PAL systems is

25Hz, and the frame rate of NTSC systems is 30Hz. The

corner frequency should be well below the frame rate.

Changing Between Video Output and

Microphone Input on a Single Connector

A single pole on a mobile phone jack can be used for

transmitting a video signal to a television or receiving

the signal from the microphone of a headset. Figure 2

shows how the MAX9517 can transmit a video signal.

Figure 3 shows how the MAX9517 can receive and

pass on the signal from a microphone.

Switching Between Video

and Digital Signals

The dual SPST analog switches and the high-imped-

ance output of the video amplifier enable video trans-

mission, digital transmission, and digital reception all

on a single pole of a connector. Figures 4, 5, and 6

show the different configurations of the MAX9517.

Selecting Between Two Video Sources

The analog switches can multiplex between two video

sources. For example, a mobile phone might have an

application processor with an integrated video encoder

and a mobile graphics processor with an integrated

video encoder, each creating a composite video signal

that is between 0 and 1V. Figure 7 shows this application

in which the MAX9517 chooses between two internal

video sources. The two analog switches can be used as

a 2:1 multiplexer to select which video DAC output is

actually filtered, amplified, and then driven out to the

connector. Close switch 1 to select the video from the

application processor. Close switch 2 to select the video

from the mobile graphics processor.

Figure 8 shows the application in which the MAX9524

chooses between two external video sources with

unknown DC bias.

Y/C Mixer with Chroma Mute

If the video application processor has two current out-

put digital-to-analog converters (DACs) for luma (Y)

and chroma (C), respectively, then the signals can be

mixed together to create a composite video signal by

summing the currents into a single resistor, as shown in

Figure 9. The composite video signal should be AC-

coupled into the MAX9524 because the composite

video signal has a positive DC level shift. The sync-tip

clamp of the MAX9524 will re-establish the DC bias

level of the signal inside the chip.

The chroma current is connected to essentially a sin-

gle-pole, double-throw (SPDT) switch. In one position,

the switch routes the chroma current into the resistor. In

the other position, the switch routes the chroma current

into ground. For the Y/C mixer to work properly, the

chroma current must be routed through analog switch 1

into the resistor.

If the chroma signal needs to be muted, then the chroma

current is shunted to ground through analog switch 2.

Analog switch 1 stays open. See Figure 10.

APPLICATION

PROCESSOR

CVBS

DAC

SHDN

+3.3V

VIDIN

BUFFER

MAX9517

LPF

AV = 2V/V

VDD

+3.3V

GND

0.1μF

VIDOUT

75Ω

220μF

CVBS

IN1

NO1

MICROCONTROLLER

IN2

NO2

COM1

COM2

Figure 1. AC-Coupled Outputs

10 ______________________________________________________________________________________

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