adg790 Analog Devices, Inc., adg790 Datasheet - Page 13

• Manufacturer Part Number: adg790
• Description: Low Voltage, Cmos Multimedia Switch
• Manufacturer: Analog Devices, Inc.

THEORY OF OPERATION
The ADG790 is a single-chip, CMOS switching solution that
comprises four SPDT switches and two 4:1 multiplexers. The
internal architecture used by the device groups the switches into
two sections, each optimized to provide the best performance in
terms of bandwidth and distortion. The on-chip parallel
interface controls the operation of all switches, allowing the
user to control switches from both sections simultaneously.
WIDE BANDWIDTH SECTION
The wide bandwidth section contains three SPDT switches
S1A/S1B-D1, S2A/S2B-D2, and S3A/S3B-D3. These switches
use a CMOS topology that ensures, besides low on resistance
and excellent flatness, the ability to switch signals up to the
supply rails. This, combined with the low switch capacitance,
provides the wide bandwidth required when switching high
frequency signals. The three SPDT switches are also optimized
to provide low propagation delay and excellent matching
between the channels, making the ADG790 ideal for applica-
tions that use multiple signals, such as universal USB switches
(full and high speed), or RGB video signals, such as VGA.
LOW DISTORTION SECTION
The low distortion section contains a single SPDT switch
(S4A/S4B-D4) and two 4:1 multiplexers (S5A/S5B/S5C/S5D-D5
and S6A/S6B/S6C/S6D-D6, respectively). The switches from
this section also use a CMOS topology that exhibits very low on
Table 4. Truth Table
S/D
1
0
0
0
0
0
0
0
0
1
X = logic state doesn’t matter.
Logic Control Inputs
IN1
X
0
0
0
0
1
1
1
1
1
IN2
X
0
0
1
1
0
0
1
1
1
IN3
X
0
1
0
1
0
1
0
1
1
S1A-D1
S2A-D2
S3A-D3
S5D-D5
S6D-D6
Off
Off
On
Off
Off
Off
On
Off
Off
S1B-D1
S2B-D2
S3B-D3
Off
On
Off
On
On
On
Off
On
On
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S4A-D4
Off
Off
On
On
On
On
Off
Off
Off
resistance and flatness while maintaining a wide bandwidth that
makes them suitable for a wide range of applications, including
low distortion audio and standard definition video signals. The
channels from the 4:1 multiplexers are matched to provide
optimal performance when used with differential signals such
as S-Video.
CONTROL INTERFACE
The operation of the ADG790 is controlled via a 4-wire parallel
interface. The logic levels applied to the IN1, IN2, and IN3 pins
control the operation of the switches from both the wide band-
width and low distortion sections, as shown in Table 4. The
shutdown pin (S/D) allows the user to disable all four SPDT
switches and force the 4:1 multiplexers into the S5B and S6B
positions, respectively. This function can be used to set up a low
speed communication protocol between the circuitry from both
sides of the device, which allows automatic configuration of the
switching function.
For example, in modern handset applications, where a single
connector is used as a multifunction communication port, the
S5B-D5 and S6B-D6 configuration obtained by setting the S/D
pin high can be used to detect the type of peripheral device
connected to the handset. The ADG790 then automatically routes
the required signals to the communication port connector.
Switch Status
S4B-D4
Off
On
Off
Off
Off
Off
On
On
On
S5A-D5
S6A-D6
Off
Off
Off
Off
Off
On
Off
On
Off
S5B-D5
S6B-D6
On
Off
Off
On
Off
Off
Off
Off
On
ADG790
S5C-D5
S6C-D6
Off
On
Off
Off
On
Off
Off
Off
Off