ADV3203 AD [Analog Devices], ADV3203 Datasheet - Page 14

• Manufacturer Part Number: ADV3203
• Manufacturer: AD [Analog Devices]

ADV3202/ADV3203
THEORY OF OPERATION
The ADV3202/ADV3203 are single-ended crosspoint arrays
with 16 outputs, each of which can be connected to any one
of 32 inputs.The 32 switchable input stages are connected to
each output buffer to form 32-to-1 multiplexers. There are 16 of
these multiplexers, each with its inputs wired in parallel, for a
total array of 512 stages forming a multicast-capable crosspoint
switch. In addition to connecting to any of the nominal inputs
(INxx), each output can also be connected to an associated OSD
input through an additional 2-to-1 multiplexer at each output.
This 2-to-1 multiplexer switches between the output of the 32-
to-1 multiplexer and the OSD input.
Decoding logic for each output selects one (or none) of the
input stages to drive the output stage. The enabled input stage
drives the output stage, which is configured as a unity-gain
amplifier in the ADV3202 (see Figure 19). In the ADV3203, an
internal resistive feedback network and reference buffer provide
for a total output stage gain of +2 (see Figure 20). The input
voltage to the reference buffer is the VREF pin. This voltage is
common for the entire chip and needs to be driven with a low
impedance to avoid crosstalk.
Figure 19. Conceptual Diagram of Single Output Channel, G = +1 (ADV3202)
Figure 20. Conceptual Diagram of Single Output Channel, G = +2 (ADV3203)
FROM INPUT
FROM INPUT
STAGES
STAGES
OSD00
OSD00
VREF
VPOS
VNEG
VPOS
VNEG
VPOS
VNEG
VPOS
VNEG
VPOS
VNEG
OSDS00
OSDS00
x1
x1
2kΩ
2kΩ
OUT00
OUT00
Rev. 0 | Page 14 of 20
Each input to the ADV3202/ADV3203 is buffered by a receiver.
The purpose of this receiver is to provide overvoltage protection
for the input stages by limiting signal swing. In the ADV3202,
the output of the receiver is limited to ±1.2 V about VREF,
while in the ADV3203, the signal swing is limited to ±1.2 V
about midsupply. This receiver is configured as a voltage
feedback unity-gain amplifier. Excess loop gain bandwidth
product reduces the effect of the closed-loop gain on the
bandwidth of the device. In addition to a receiver, each input
also has a sync-tip clamp for use in ac-coupled applications.
This clamp is either enabled or disabled according to the 193
serial data bit. When enabled, the clamp forces the lowest video
voltage to the voltage on the VCLAMP pin. The VCLAMP pin
is common for the entire chip and needs to be driven with a low
impedance to avoid crosstalk.
The output stage of the ADV3202/ADV3203 is designed for low
differential gain and phase error when driving composite video
signals. It also provides slew current for fast pulse response
when driving component video signals.
The outputs of the ADV3202/ADV3203 can be disabled to
minimize on-chip power dissipation. When disabled, a series of
internal amplifiers drive internal nodes such that a wideband
high impedance is presented at the disabled output, even while
the output bus is under large signal swings. (In the ADV3203,
there is 4 kΩ of resistance terminated to the VREF voltage by
the reference buffer). This high impedance allows multiple ICs
to be bussed together without additional buffering. Care must
be taken to reduce output capacitance, which results in more
overshoot and frequency domain peaking. In addition, when
the outputs are disabled and driven externally, the voltage
applied to them should not exceed the valid output swing range
for the ADV3202/ADV3203 to keep these internal amplifiers in
their linear range of operation. Applying excess voltage to the
disabled outputs can cause damage to the ADV3202/ADV3203
and should be avoided (see the Absolute Maximum Ratings
section for guidelines).
Figure 21. Conceptual Diagram of Sync-Tip Clamp in an
VCLAMP
IN00
CAPACITOR
OFF-CHIP
AC-Coupled Application
VPOS
VNEG
5µA
VPOS
TO INPUT
RECEIVER
rd