AD831 OUT Pin AC-coupled

Can anyone tell me what is RT and CC for as shown in Figure. 10 of AD831 datasheet? I read it said output pin must be "ac-coupled to the load", so is this a high-pass filter network?

Besides, I am inputting 50kHz signal monotone into LO, should I consider the impedance matching as suggested? Will removing it a big problem for my signal?



  • 0
    •  Analog Employees 
    on Jan 9, 2016 7:05 AM

    Hi, x-mengao,

        In Fig. 10, the device's IF output is sitting at 1/2 of dc supply, so Cc is needed to block the flow of DC current into the load, and the value depends on the high-pass cutoff frequency desired.  If dc coupling is needed, then the load should be sitting at the same nominal dc level to prevent excess dc current to flow.

        Since the IF pin has a near zero output impedance, RT is added in series to present a finite output impedance, e.g., to drive filters that want to see a source impedance (say, 50-ohm).


  • 0
    •  Analog Employees 
    on Aug 2, 2018 3:19 PM
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