AD9680 input impedance matching questions

good day

I have several questions regarding the input interface of the AD9680.

I would like to design a matching network using Snp file. Firstly I don't understand why S2p are provided whereas I expect only file having S11 parameter since the purpose is to provide matching impedance. In addition several files are provided, I don't know which one to use. Could you please clarify which context for each file?

In the datasheet page 36 at table 9 parameter values are provided for the components shown in figure 115, I was wondering if these values are still ok whatever differential input impedance value is set (see figure 116 where different resistors can be selected via registers). Is it possible to attach a drawing of an example of matching specifying the context ( frequency range...)

Thank you in advance for your reply

Best regards

Raphael

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    •  Analog Employees 
    on Oct 18, 2016 4:21 PM

    Hello Raphael

    I used the ideal balun component in ADS to simulate my circuit. I could not find an equivalent in QUCS. However, I can get the same response by running single ended s-parameter simulation and then using the following equation

    SDD11 = 0.5*(S[1,1]-S[1,2]-S[2,1]+S[2,2])

    See below for schematic

    See below for results

    See below for the same simulation using ADS.

    Thanks

    Umesh

  • Hi Umesh,

    I believe the S2P file is the input impedance of the ADC when it is configured for 200Ohms. The ADS simulation shows a large variation in the impedance from 1 MHz to 2GHz. Since the balun used here is ideal, it must be the impedance of the ADC itself. I intend to use this for digitising a signal bandwidth from 200MHz to 500MHz. I plan to use a 1:4 transformer to translate the 200Ohm to 50Ohm and avail benefit from the voltage gain. Should I use impedance matching networks in between to further match it for this wide variation?

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  • Hi Umesh,

    I believe the S2P file is the input impedance of the ADC when it is configured for 200Ohms. The ADS simulation shows a large variation in the impedance from 1 MHz to 2GHz. Since the balun used here is ideal, it must be the impedance of the ADC itself. I intend to use this for digitising a signal bandwidth from 200MHz to 500MHz. I plan to use a 1:4 transformer to translate the 200Ohm to 50Ohm and avail benefit from the voltage gain. Should I use impedance matching networks in between to further match it for this wide variation?

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