LMH6583_14 Datasheet, PDF (12/24 Pages) Texas Instruments – LMH6583 16x8 550 MHz Analog Crosspoint Switch, Gain of 2

LMH6583
SNOSAP5E – APRIL 2006 – REVISED MARCH 2013
www.ti.com
2
OUTPUT CONNECTED DIRECTLY
1
0
-1
NO EXPANSION
-2
-3
-4
-5
-6 ^{VS = ±3.3V}
V_OUT = 2 V_PP
-7
R_L = 150:
-8
1
10
100
FREQUENCY (MHz)
1000
Figure 36. Input Expansion Frequency Response
2
OUTPUT CONNECTED DIRECTLY
1
0
-1
NO EXPANSION
-2
-3
-4
-5
-6 ^{VS = ±5V}
V_OUT = 2 V_PP
-7
R_L = 150:
-8
1
10
100
FREQUENCY (MHz)
1000
Figure 37. Input Expansion Frequency Response
DRIVING CAPACITIVE LOADS
Capacitive output loading applications will benefit from the use of a series output resistor R_OUT. Capacitive loads
of 5 pF to 120 pF are the most critical, causing ringing, frequency response peaking and possible oscillation. For
applications where maximum frequency response is needed and some peaking is tolerable, the value of R_OUT
can be reduced slightly from the recommended values. When driving transmission lines the 50Ω or 75Ω
matching resistor makes the series output resistor unnecessary.
USING OUTPUT BUFFERING TO ENHANCE BANDWIDTH AND INCREASE RELIABILITY
The LMH6583 crosspoint switch can offer enhanced bandwidth and reliability with the use of external buffers on
the outputs. The bandwidth is increased by unloading the outputs and driving a higher impedance. The 1 kΩ load
resistor was chosen to provide the best performance on our evaluation board. See Figure 9 in Typical
Performance Characteristics for an example of bandwidth achieved with less loading on the outputs. For this
technique to provide maximum benefit a very high speed amplifier such as the LMH6703 should be used, as
shown in Figure 38.
Besides offering enhanced bandwidth performance using an external buffer provides for greater system
reliability. The first advantage is to reduce thermal loading on the crosspoint switch. This reduced die
temperature will increase the life of the crosspoint. The second advantage is enhanced ESD reliability. It is very
difficult to build high speed devices that can withstand all possible ESD events. With external buffers the
crosspoint switch is isolated from ESD events on the external system connectors.
LMH6583
OUTPUT
BUFFER
R_L
1 k:
LMH6703
+
-
560:
560:
V_OUT
Figure 38. Buffered Output
12
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