lmh6584 National Semiconductor Corporation, lmh6584 Datasheet - Page 15

• Manufacturer Part Number: lmh6584
• Description: Lmh6584/lmh6585 32x16 400 Mhz Analog Crosspoint Switches, Gain Of 1, Gain Of 2
• Manufacturer: National Semiconductor Corporation

(Only 4 input and 4 output channels shown for illustration
Input expansion requires more planning is also quite easy, but
there are two different options for arranging the output termi-
nation resistors. As show in Figure 4 and Figure 5 there are
two ways to connect the outputs of the crosspoint switches.
In Figure 4 the crosspoint switch outputs are connected di-
rectly together and share one termination resistor. This is the
easiest configuration to implement and has only one draw-
back. Because the disabled output of the unused crosspoint
(only one output can be active at a time) has a small amount
of capacitance, the frequency response of the active cross-
point will show peaking
As illustrated in Figure 5 each crosspoint output can be given
its own termination resistor. This results in a frequency re-
sponse nearly identical to the non expansion case. There is
one drawback for the gain of 2 crosspoint, and that is gain
error. With a 75Ω termination resistor the 1250Ω resistance
of the disabled crosspoint output will cause a gain error. In
order to counteract this the termination resistors of both cross-
FIGURE 2. Frequency Response for Buffered and
FIGURE 3. Output Expansion no Buffers
Unbuffered Output expansion
purposes.)
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points should be adjusted to approximately 71Ω. This will
provide very good matching, but the gain accuracy of the sys-
tem will now be dependent on the process variations of the
crosspoint resistors which have a variability of approximately
±20%.
(Only 4 input and 4 output channels shown for illustration
(Only 4 input and 4 output channels shown for illustration
FIGURE 5. Input Expansion with Separate Termination
FIGURE 4. Input Expansion with Shared Termination
purposes.)
purposes.)
Resistors
Resistors
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