Questions bout the intput and output of the AD8302?

HI!

My purpose is to detect the impedance information of two signals. And the two input signal are about 2v, 100KHz, then it pass a resistance attenuation network(refer to the Datasheet in page 19). Now, the signal attenuates to about 200mV,The schematic as follow.

Q:

1. the formal input signal is shaken and distorted by the attenuation network, how can I eliminate the distort?

2. I have change the value of R167 and R178 to 1KΩ, what is  the influence of this changes?(If I set the two resistors to 52Ω , the input signal will disappear )   

3. no matter I change the input signal, the average of VMAG stays at about 1V and VPHS stays at about 1.04V, where is the problem?

looking  forward your reply!

Parents
  • 0
    •  Analog Employees 
    on Jul 10, 2018 8:17 PM
    • C16 and C17 need to be AC grounded
    • The signal being distorted and shaky could be a lot of things.  I would remove C15 and C18 and probe R13 and R15.  Is the signal still distorted?  I would work my way towards the ADG836, probing at various points, checking the signal to see if its distorted. 
    • Is it distorted at the inputs of the ADG836?
    • How are you changing the signal amplitudes?  For best behavior and the greatest measurement range, one of the two signals needs to be set at -30 dBm (7.07mVrms), while the other can range from -60 dBm (223 uVrms) to 0 dBm  (223 mVrms); equivalent voltages are assuming 50 Ohm terminations.
Reply
  • 0
    •  Analog Employees 
    on Jul 10, 2018 8:17 PM
    • C16 and C17 need to be AC grounded
    • The signal being distorted and shaky could be a lot of things.  I would remove C15 and C18 and probe R13 and R15.  Is the signal still distorted?  I would work my way towards the ADG836, probing at various points, checking the signal to see if its distorted. 
    • Is it distorted at the inputs of the ADG836?
    • How are you changing the signal amplitudes?  For best behavior and the greatest measurement range, one of the two signals needs to be set at -30 dBm (7.07mVrms), while the other can range from -60 dBm (223 uVrms) to 0 dBm  (223 mVrms); equivalent voltages are assuming 50 Ohm terminations.
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