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AFE7222: Questions about Tx/Rx Path circuit

Nicky Lim
Genius 3195 points
Part Number: AFE7222

Hello,

Make AFE7222 schematic as attached. 

And there are 2 or 3 options for Tx & Rx path.

1. Tx Path :  will use default path(Resistor path) if there is no problem.

                    two other options(RF Transformer path & Capacitor path) will be used if resistor path has problem, and if those options doesn't have problem.

2. Rx Path : will select between  RF transformer path and capacitor path if there is no problem.

Requirements.

1. Please review AFE7222 Tx / Rx path circuit and let me get your result.

2. Please see attached document and schematic.

Regards,

Nicky

Questions about AFE722_20170823.docx

Schemaitc of AFE7222.pdf

  • 0
    TI__Genius 12965 points
    Nicky,

    Someone will get back with you soon.

    Ken.
  • 0 in reply to Ken C
    Genius 3195 points
    Hi Ken,


    When can I get the answer?
    Please let me get it ASAP.

    Regards,
    Nicky
  • 0 in reply to Nicky Lim
    TI__Genius 12965 points
    I have notified the responsible engineers and they will be getting back to you soon.

    Ken.
  • 0
    TI__Mastermind 18095 points

    Nicky:

    First let's focus on the DAC interface.  I do not know what modulator you are interfacing to and hence, I do not know what common mode voltage that you need to achieve.  That said, the passive resistor network appears incorrect.

    You have some system constraints to adhere to.  The DAC voltage (Vd) should be 3.0V.  The full scale current is 20 mA.  I will assume that the modulator common mode voltage is 1.7V.  You have a choice on what to set the Vdd voltage. In your case you chose 3.8V.

    With these parameters I calculate (ideally): R1 = 54 ohms, R2 = 274 ohms, R3 = 359 ohms.  This translates to an insertion loss of the passive network at about 5 dB.

    The receiver schematic looks good.  One suggestion is to replace the transformers with the ADT1-1WT.  This is a change we implemented on our RevC board.

    --RJH

  • 0 in reply to RJ Hopper
    Genius 3195 points

    Hi RJ,

    ▶ The following table shows modulator specifications.

    Modulator spec

    Specification

    Unit

    Min.

    Typ.

    Max.

    Input resistance

     

    >100

     

    Kohm

    Input capacitance

     

    <10

     

    pF

    Input common mode voltage (Common voltage is supplied from external.)

    1.4

    1.5

    1.6

    V

    Input differential peak-to-peak input voltage

     

    1.00

    2.00

    Vppd

    ▶ Ok, AVDD3_DAC of AFE7222 (pin #11, #14 and #17) is 3.0V

    ▶ Common mode voltage of the modulator used is 1.5V and Vdd is 3.8V.

       In this case, what is the value for R1, R2 and R3?

    Please tell me how to calculate the R1, R2 and R3.

    ▶ Please tell me how to calculate the insertion loss of the passive network.

    Regards,

    Nicky

  • 0 in reply to Nicky Lim
    TI__Mastermind 18095 points

    Nicky:

    With Vcm = 1.5V and Vdd = 3.8 V then the network is (ideally): R1 = 54 ohms, R2 = 317 ohm, R3 = 317 ohm.  This is 6 dB insertion loss.  --RJH

    Equations below for reference.