GX214A Просмотр технического описания (PDF) - Gennum -> Semtech
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GX214A Datasheet PDF : 5 Pages
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APPLICATION INFORMATION
The circuit layout of any wideband circuit is critical. Good
high frequency design practice, proper lead dress and
PCB component placement along with a well regulated and
decoupled power supply will assure optimum performance
of the crosspoint.
The GX214A is non-inverting. The inputs are buffered and
require 75Ω line terminating resistors when driven from 75Ω
cable. The inputs may be driven directly from an amplifier
which has low output impedance.
The output of the GX214A must be buffered to drive 7 Ω
lines. The addition of an amplifier/buffer also allows adjustments
to be made to the gain, offset and frequency response of
the circuit.
An external load current of 2 to 8mA should be supplied
from each output bus to negative supply. For most applications
a load resistor of 2.67kΩ, 1% is recommended to minimize
offset drift with temperature. In order to improve differential
phase and tighten the insertion loss tolerance, an external
constant current active load may be substituted for the
load resistor. Note however, that since only one GX214A
output drives the output bus at any one time, only one
external load is needed for the bus.
A typical application is shown below. Two GX214A ICs are
paralleled to form an 8x1 crosspoint matrix. The three
address lines make use of the A0, A1 and CS inputs. If more
than two devices are used in parallel, a decoder is necessary
in order to generate the extra address inputs.
Signal Ground (SG) pins 2, 4 and 6 must be joined together
and preferably form part of a ground plane. The Signal
Ground must also be connected to the ±8V power supply
ground. The potential of the Logic Ground (LG) pin 9 can
deviate from the Signal Ground by ±0.5V maximum. Alternatively,
the signal and logic grounds can be joined together at one
point only.
Depending on the application and the speed of the logic
family used, latches may be required for synchronization
where timing delays are critical. The active switching
circuitry of the GX214A ensures low crosstalk and high per-
formance over an input voltage range of -1.2 to +5.0 volts.
INPUTS
V0
V1
V2
V3
75
75 75 75
VIDEO SWITCHES
0.1
+8V
1 IN 0
2 SG
3 IN 1
4 SG
5
IN 2
6 SG
7
IN 3
+V 14
13
A0
A 1 12
CS 11
10
OUT
9
LG
-V 8
0.1
-8V
+8V
0.1
A0
A 1 ADDRESS
A2
V4
V5
V6
V7
75 75
75
75
1 IN 0
2 SG
3 IN 1
4 SG
5 IN 2
6 SG
7 IN 3
+V 14
A 0 13
A 1 12
11
CS
OUT 10
9
LG
-V 8
0.1
-8V
2.67 K
GAIN, OFFSET, FREQUENCY
RESPONSE ADJUSTMENTS
75
AMPLIFIER/BUFFER
All resistors in ohms, all capacitors
in microfarads, unless otherwise stated
V OUT
Fig. 1 8x1 Video Multiplexer Incorporating Two GX214A Devices
3
520 - 5 - 1
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