ADV7282 datasheet(16/32 Pages) AD

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ADV7282

Data Sheet

Rev. A | Page 16 of 32

INPUT NETWORKS

An input network (external resistor and capacitor circuit) is

required on the AINx input pins of the ADV7282/ADV7282-M.

The components of the input network depend on the video

format selected for the analog input.

SINGLE-ENDED INPUT NETWORK

Figure 9 shows the input network to use on each AINx input

pin of the ADV7282/ADV7282-M when any of the following

video input formats is used:

•

Single-ended CVBS

•

YC (S-Video)

•

YPrPb

51Ω

AIN3

INPUT

CONNECTOR

VIDEO INPUT

FROM SOURCE

24Ω

100nF

EXT

ESD

Figure 9. Single-Ended Input Network

The 24 Ω and 51 Ω resistors supply the 75 Ω end termination

required for the analog video input. These resistors also create a

resistor divider with a gain of 0.68. The resistor divider attenuates

the amplitude of the input analog video and scales the input to the

ADC range of the ADV7282/ADV7282-M. This allows an input

range to the ADV7282/ADV7282-M of up to 1.47 V p-p. Note

that amplifiers within the ADC restore the amplitude of the

input signal so that signal-to-noise ratio (SNR) performance is

maintained.

The 100 nF ac coupling capacitor removes the dc bias of the analog

input video before it is fed into the AINx pin of the ADV7282/

ADV7282-M. The clamping circuitry within the ADV7282/

ADV7282-M restores the dc bias of the input signal to the

optimal level before it is fed into the ADC of the ADV7282/

ADV7282-M.

DIFFERENTIAL INPUT NETWORK

Figure 10 shows the input network to use when differential

CVBS video is input on the AINx input pins of the ADV7282/

ADV7282-M.

AIN1

AIN2

INPUT

CONNECTOR

INPUT

CONNECTOR

VIDEO INPUT

FROM SOURCE

EXT

ESD

1.3kΩ

100nF

1.3kΩ

100nF

430Ω

Figure 10. Differential Input Network

Fully differential video transmission involves transmitting

two complementary CVBS signals. Pseudo differential video

transmission involves transmitting a CVBS signal and a source

ground signal.

Differential video transmission has several key advantages over

single-ended transmission, including the following:

•

Inherent small signal and large signal noise rejection

•

Improved EMI performance

•

Ability to absorb ground bounce

Resistor R1 provides the RF end termination for the differential

CVBS input lines. For a pseudo differential CVBS input, a value

of 75 Ω is recommended for R1. For a fully differential CVBS

input, a value of 150 Ω is recommended for R1.

The 1.3 kΩ and 430 Ω resistors create a resistor divider with a

gain of 0.25. The resistor divider attenuates the amplitude of the

input analog video, but increases the input common-mode range

of the ADV7282/ADV7282-M to 4 V p-p. Note that amplifiers

within the ADC restore the amplitude of the input signal so that

SNR performance is maintained.

The 100 nF ac coupling capacitor removes the dc bias of the analog

input video before it is fed into the AINx pin of the ADV7282/

ADV7282-M. The clamping circuitry within the ADV7282/

ADV7282-M restores the dc bias of the input signal to the

optimal level before it is fed into the ADC of the ADV7282/

ADV7282-M.

The combination of the 1.3 kΩ and 430 Ω resistors and the

100 nF ac coupling capacitors limits the current flow into the

ADV7282/ADV7282-M during short-to-battery (STB) events

(see the Short-to-Battery Protection section).

To achieve optimal performance, the 1.3 kΩ and 430 Ω resistors

must be closely matched; that is, all 1.3 kΩ and 430 Ω resistors

must have the same resistance tolerance, and this tolerance must

be as low as possible.

SHORT-TO-BATTERY PROTECTION

In differential mode, the ADV7282/ADV7282-M is protected

against short-to-battery (STB) events by ac coupling capacitors

(see Figure 10). The input network resistors are sized to reduce

the current flow during an STB event, thus preventing damage to

the resistors. The R1 resistor is protected because no current or

limited current flows through it during an STB event.

The ADV7282/ADV7282-M provides two STB diagnostic pins

that can be used to generate an interrupt when an STB event

occurs. For more information, see the Short-to-Battery (STB)

Diagnostics section.

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