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ADG936 RF switch and DC Bias

I am planning to use AD9122 DAC outputs with 0.5V bias as inputs to ADG936 (at A and B inputs), for DC-100MHz signals. I want to make sure that the 0.5V dc bias on the DAC signal is available and not blocked (except for insertion loss at DC) at the RFC outputs of the ADG936. I will need this bias level to drive the ADL5375 IQ modulator.

  • Hi arvabj,

    The ADG936 can pass DC signals so you will have no problem with using the DC bias at the output. 

    Regards,

    Eric.

  • Hi Arvabj,

    I think bandwidth will be important to you here.  The ADG9xx family of switches are our highest bandwidth switches but the CM voltage you need is too much for them.  So, with regards our regular CMOS options, perhaps the ADG772 could be an option for you. It will depend on the frequency and amplitude of your IQ signals.  Here is a link to the ADG772 product page on analog.com .  http://www.analog.com/en/switchesmultiplexers/analog-switches/adg772/products/product.html .  You can check its performance data using the datasheet. 

    On your demodulator questions, I think it best for you to post that in the RF Components of EZone to get a comment from that group. 

    Regards,

    Eric.

  • Hi AB,

    I think the ADG772 should be considered for this application.  Looking at your specifications, if you use a Vdd in the region of 3.3V it will work from DC-100MHz with a 0dBm signal on a 2.5V CM.  The Insertion loss is good and flat up to 100MHz.

    Regards,

    Eric.

  • Hi Eric,

    Thanks very much for your response. I have another question regarding these switches. I have an application as shown in attached image. I need a switch/ mux solution to select between IQ signals out of two IQ demodulators in the RF receive chain. The selected IQ is provided to the AD8366 VGA. I was hoping that using 2 ADG936 switches will be a good solution. But the output common mode DC bias levels from the AD demodulators (2.5V typical) and input DC bias requirements to the AD8366 (1.5V minimum) are quite high for the ADG936. Could you please recommend a switch/mux solution from AD that would work for this application ?

    I do have the provision to completely turn of the power supply to the demodulators. So i can turn-on one demodulator only at a time and cut-off supply to the other. With this provision, can i simply tie the IQ signals of the two demodulators together without the need for switch/ muxes ?

  • Eric,

    Thanks ... I looked at the ADG772 datasheet. Our requirements for the IQ signal inputs are:

    DC-100 MHz

    0dBm differential swing (I and Q) is maximum input amplitude to the switches

    Input common mode of 2.5V

    The ADG772 has 630MHz 3dB BW and maximum analog input is Vdd. So looks like with Vdd of  3.3V, our requirements should be met. Is my analysis correct ?

    Thanks,

    AB

  • Hi Eric,

    Sorry to bother you again. Can you please let me know if the ADG772 solution will work, based on the requirements that i mentioned in my previous post ? the key question is the ability to pass DC-100 MHz with 2.5V DC bias on input signal and 0dBm peak input amplitudes.

    Thanks again,

    AB