Data Sheet ADV7283
Rev. A | Page 13 of 21
INPUT NETWORKS
An input network (external resistor and capacitor circuit) is
required on the A
IN
x input pins of the ADV7283. The
components of the input network depend on the video format
selected for the analog input.
SINGLE-ENDED INPUT NETWORK
Figure 6 shows the input network to use on each A
IN
x input pin
of the ADV7283 when any of the following video input formats
are used:
• Single-ended CVBS
• Y/C (S-Vide o)
• YPrPb
Figure 6. 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 ADV7283. This allows an input range of up to
1.47 V p-p. Note that amplifiers within the ADC restore the
amplitude of the input signal so 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 A
IN
x pins of the ADV7283.
The clamping circuitry within the ADV7283 restores the dc bias
of the input signal to the optimal level before it is fed into the
ADC of the ADV7283.
DIFFERENTIAL INPUT NETWORK
Figure 7 shows the input network to use when differential
CVBS video is input on the A
IN
x input pins of the ADV7283.
Figure 7. 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
• Inherent small signal and large signal noise rejection
• Improved EMI performance
• An 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 ADV7283 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 capacitors remove the dc bias of the
analog input video before it is fed into the A
IN
x pins of the
ADV7283. The clamping circuitry within the ADV7283 restores
the dc bias of the input signal to the optimal level before it is fed
into the ADC of the ADV7283.
The combination of the 1.3 kΩ and 430 Ω resistors and the
100 nF ac coupling capacitors limits the current flow into the
ADV7283 during 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 ADV7283 is protected against STB
events by the external 100 nF ac coupling capacitors (see
Figure 7). The external input network resistors are sized to be
large enough to reduce the current flow during an STB event,
but small enough to avoid affecting the operation of the
ADV7283.
The power rating of the input network resistors must be chosen
withstand the high voltages of STB events. Similarly, ensure that
the breakdown voltage of the ac coupling capacitors is robust
enough to handle STB events.
The R1 resistor is protected because no current or limited current
flows through it during an STB event.
51Ω
A
IN
3
INPUT
CONNECTOR
VIDEO INPUT
FROM SOURCE
24Ω
100nF
EXT
ESD
12347-006
A
IN
1
A
IN
2
POSITIVE
INPUT
CONNECTOR
NEGATIVE
INPUT
CONNECTOR
VIDEO INPUT
FROM SOURCE
EXT
ESD
R1
1.3kΩ
100nF
1.3kΩ
100nF
430Ω
430Ω
12347-007
