FS401LF datasheet(95/104 Pages) ETC2

95 / 104 page

FS401, FS403

PRODUCT SPECIFICATION

REV. NO. 1.7

JANUARY 24, 2007

7. Application Notes

7.1 Circuit Example - PC

RGB video signals and the vertical and horizontal sync signals are intercepted by tapping connections to

the VGA connector. Typically, control of the FS400 will be through the serial interface. S-video and

Composite Video outputs are fed to connector that should be located at the board edge. Power is

derived from +3.3 volt analog and digital supplies. It is recommended that the analog supply be clean of

noise.

Input impedance of the A/D converters exceeds 500K and will not load VGA RGB lines. Shunt 100pF

capacitors and 110

Ω series resistors form a low pass filter with 15 MHz cutoff. Filtering the incoming

video has two functions:

equalizing the intensities of vertical lines

eliminating sampling noise.

Outgoing video is filtered by low pass Bessel filters with 10 MHz cutoff. An optional low pass filter has

two functions:

removal of steps from the Composite Video output

limiting the bandwidth of outgoing video.

For higher definition of horizontal frequencies, a sinx/x correction filter should be incorporated to

compensate for 1 dB sampling loss of the D/A converters. Schottky diode clamps protect the FS400 from

high voltage transients.

-40.00

-30.00

-20.00

-10.00

0.00

10.00

100

Frequency (MHz)

Figure 21. Video Filter Response

0.00

10.00

20.00

30.00

40.00

50.00

100

Frequency (MHz)

Figure 22. Video Filter Delay

VTIN is derived from the bias voltage across RREF that is established by the internal reference voltage

available at VREF. RREF is split into two resistors with series resistance to set the RREF current and ratio to

establish the VTIN voltage.

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