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MPC506 Crosstalk

Toshio Ushikubo
Mastermind 9620 points
Other Parts Discussed in Thread: MPC508

Hello, 

MPC508 datasheet has “CROSSTALK vs SIGNAL FREQUENCY” characteristics on page4, but does not have test circuit information.

Please let me known test circuit information and what is “Rs” in the Figure.

Regards.

  • 0
    TI__Guru* 93105 points

    Ushikubo-san,

    The MPC508 is a legacy product about 25 years old and we do not have any of its original documentation. I searched but nothing was found. Thus, I can only provide some ideas I have about how the crosstalk vs. frequency test was performed.

    I think the test might have been set up in a similar manner as is shown Fig. 4, for another legacy multiplexer product,the  MPC100:

    http://www.ti.com/product/mpc100

    The RF generator is terminated in that example with two 50 Ohm resistors in series, to ground. A series resistance - which I presume is Rs for the MPC508 - is connected to the divider point of the two 50 Ohm resistors. One Rs is added in series from the divider point to each multiplexer input.

    The MPC100 shows an RC filter at the multiplexer output, followed by buffer amplifier stage. This stage's purpose is to buffer the multiplexer output from the 50 Ohm input impedance of a spectrum analyzer. The MPC508 is a much lower bandwidth than the MPC100 and I suspect the measurement was made using a high input impedance, 6 1/2 digit DVM, instead of a spectrum analyzer. Such DVMs usually have sufficient bandwidth for a 10 kHz measurement.

    I would terminate each of the multiplex outputs with a high resistance load resistor (~100 k) to ground. One input would be turned ON and driven with the input signal. Then, the DVM would be connected to each of the OFF channels one at a time. The DVM would be used to measure the low level signal at the output of the OFF channels.

    Since we do not know for certain how this was originally measured all I can offer is my proposal.

    Regards, Thomas

    PA - Linear Applications Engineering