AD8302 impedance and output

I just have several questions about AD8302.

1. What is the input impedance of the chip when it is connected to the circuit but without a power supply?

2. I got an output from AD8302 voltage larger than 1.8V. What should be the problem, I just design the measurement board same as its datasheet.

Thank you so much for the help.

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  • 0
    •  Analog Employees 
    on Nov 14, 2020 1:25 AM 2 months ago

    Hi YZang92,

    1. Z_in without power is not something we normally check, but it's likely to be rather high Z for small signal, but low Z for large signal, as the ESD protection diodes begin to conduct. Such large signals are not where anyone should be using the device.

    2. Perhaps the feedback connection was not connected. You'll notice each of the two outputs has a feedback connection to the MSET or PSET pin. Without that connection, the output will rail one way or the other.

    -Bruce H.

  • Thanks for the reply.

    Actually I was measuring the S-paras of a whole circuit with AD8302 connected with a voltage divider to a microcontroller by VNA. My problem is when I add power supply to the AD8302, the S-para of my whole circuit changes. Thus, I am wondering if the Z_in of AD8302 changes a lot which causes the RF signal changes.

    For the second one, I connect MSET and PSET to the two outputs directly as the datasheet(basic connection), is that right? Is there anything else that I need connect to?

  • +1
    •  Analog Employees 
    on Nov 20, 2020 5:59 PM 1 month ago in reply to YZang92

    Hi YZang92,

    1)  Have a look at datasheet Figure 1, Circuit A. With VPOS= 0 volts, the range of input RF voltage will be less before the ESD diodes conduct. You might want to double check your RF input drive levels. Datasheet page 2 specs input RF level as -13dBV max, which is 224mV rms.

    2)  Datasheet Figures 4 and 14 both convey the basic hookup. If any doubt, you could try out and compare to a factory eval board to confirm proper operation.

Reply
  • +1
    •  Analog Employees 
    on Nov 20, 2020 5:59 PM 1 month ago in reply to YZang92

    Hi YZang92,

    1)  Have a look at datasheet Figure 1, Circuit A. With VPOS= 0 volts, the range of input RF voltage will be less before the ESD diodes conduct. You might want to double check your RF input drive levels. Datasheet page 2 specs input RF level as -13dBV max, which is 224mV rms.

    2)  Datasheet Figures 4 and 14 both convey the basic hookup. If any doubt, you could try out and compare to a factory eval board to confirm proper operation.

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