AD8188ARUZ Analog Devices Inc, AD8188ARUZ Datasheet - Page 19

• Manufacturer Part Number: AD8188ARUZ
• Description: IC,ANALOG MUX,TRIPLE,2-CHANNEL,TSSOP,24PIN,PLASTIC
• Manufacturer: Analog Devices Inc
• Type: Analog Multiplexerr

Specifications of AD8188ARUZ

• Function: Multiplexer
• Circuit: 3 x 2:1
• On-state Resistance: 350 mOhm
• Voltage Supply Source: Single Supply
• Voltage - Supply, Single/dual (±): 3.5 V ~ 5.5 V
• Current - Supply: 15mA
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 24-TSSOP (0.173", 4.40mm Width)
• Package: 24TSSOP
• Multiplexer Architecture: 2:1
• Maximum Turn-off Time: 17(Typ)@5V ns
• Maximum Turn-on Time: 4(Typ)@5V ns
• Power Supply Type: Single
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

These two techniques can also be combined. Typically, crosstalk
between the RGB signals from the same source is less objectionable
than crosstalk between two different sources. The former can
cause a color or luminance shift, but spatially, everything is
coherent. However, the crosstalk signals from two uncorrelated
sources can create ghost images that are far more objectionable.
A technique for minimizing crosstalk between two different
sources is to create two separate V
from each source can be connected to their own V
minimizing crosstalk between sources.
AD8189
When using the gain-of-two AD8189 in a simple ac-coupled
application, there is a dynamic range limitation at the output
caused by its higher gain. At the output, the gain-of-two
produces a signal swing of 1.4 V, but the ac-coupling doubles
this required amount to 2.8 V. The AD8189 outputs can only
swing from 1.4 V to 3.6 V on a 5 V supply, so there are only
2.2 V of dynamic signal swing available at the output.
A standard means for reducing the dynamic range requirements
of an ac-coupled video signal is to use a dc restore. This circuit
works to limit the dynamic range requirements by clamping the
black level of the video signal to a fixed level at the input to the
amplifier. This prevents the video content of the signal from
varying the black level, as happens in a simple ac-coupled circuit.
DC RESTORE
After ac-coupling a video signal, it is necessary to use a dc
restore to establish where the black level is. Usually, this appears
at the end of a video signal chain. This dc restore circuit needs
to have the required accuracy for the system. It compensates for
all the offsets of the preceding stages. Therefore, if a dc restore
circuit is to be used only for dynamic range limiting, it does not
require great dc accuracy.
A dc restore circuit using the AD8189 is shown in Figure 56.
Two separate sources of RGB video are ac-coupled to the 0.1 μF
2.4V MIN
0.8V MIN
3.48kΩ
1.5kΩ
5V
10µF
1.5V
+
HSYNC
MID
SEL A/B
V
0.1µF
REF
circuits. Then, the inputs
EN A0 A1 A2
D1
D2
D3
GND
ADG786
LOGIC
Figure 56. AD8189 AC-Coupled with DC Restore
V
MID
5V
DD
node,
S1A
S1B
S2A
S2B
S3A
S3B
V
SS
Rev. 0 | Page 19 of 24
GRNA
GRNB
REDA
BLUA
REDB
BLUB
V
REF
0.1µF
0.1µF
0.1µF
0.1µF
0.1µF
0.1µF
input capacitors of the AD8189. The input points of the
AD8189 are switched to a 1.5 V reference by the ADG786,
which works in the following manner:
•
•
There are two considerations for sizing the input coupling
capacitors. One is the time constant during the H-pulse
clamping. The other is the droop associated with the capacitor
discharge due to the input bias current of the AD8189. For the
former, it is better to have a small capacitor, but for the latter, a
larger capacitor is better.
The on resistance of the ADG786 and the coupling capacitor
form the time constant of the input clamp. The ADG786 on
resistance is 5 Ω maximum. With a 0.1 μF capacitor, a time
constant of 0.5 μs is created. Thus, a sync pulse of greater than
2.5 μs causes less than 1% error. This is not critical because the
black level from successive lines is very close and the voltage
changes little from line to line.
A rough approximation of the horizontal line time for a graphics
system is 30 μs. This varies depending on the resolution and the
vertical rate. The coupling capacitor needs to hold the voltage
relatively constant during this time, while the input bias current
of the AD8189 discharges it.
The change in voltage is I
capacitance. With an I
0.1 μF coupling capacitor, the amount of droop is 0.75 mV. This
is roughly 0.1% of the full video amplitude and is not observable
in the video display.
The SEL A/ B signal selects the A or B input to the AD8189. It
also selects the switch positions in the ADG786 such that the
same selected inputs are connected to V
During the horizontal interval, all of the RGB input signals are
at a flat black level. A logic signal that is low during HSYNC is
applied to the EN of the ADG786. This closes the switches and
clamps the black level to 1.5 V. At all other times, the switches
are off and the node at the inputs to the AD8189 floats.
D
IN0A
IN1A
IN2A
IN0B
IN1B
IN2B
V
GND
REF
3V TO 5V 5V
DV
V
EE
CC
V
SEL A/B
CC
B
of 2.5 μA, a line time of 30 μs, and a
×2
×2
×2
B
AD8189
times the line time divided by the
OE
OUT0
OUT1
OUT2
RED
GRN
BLU
AD8188/AD8189
REF
when EN is low.