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Original question:

AFE7071: Multi-carrier supported ?

AFE7071: What ACLR can be expected for output

XIN LI
Prodigy 180 points
Part Number: AFE7071


Hello,

I want to know what is the ACLR can be achieved (except the phase noise of the external LO) at the output od IQ modulator if the signal BW is 25kHz (so adjacent channel is also 25kHz), I didn't find the info in datasheet. We need -70dBc at 25kHz offset of the fundamental signal. 

Thanks,

XL

  • 0
    TI__Mastermind 18095 points

    XL:

    25 kHz is a very narrow bandwidth.  I recommend to use the published IP3 parameter of 19 dBm to estimate the ACPR in your case.  Working a bit backwards, you can achieve 70 dBc by:

    IP3 = 70 / 2 + Pout  ==> Pout = -16 dBm

    So with the output power reduced to -16 dBm you can achieve 70 dBc; however, that does not take into account thermal noise as well as LO phase noise.  A narrow band output of -16 dBm is on the lower side and I think thermal noise will come into the picture.  My guess is that 70 dBc will not quite be attainable.  If you can shift the signal to a low IF of, say, 5 MHz, then you can escape some of the problem issues related to carrier feedthrough, sideband suppression, and LO phase noise.

    -RJH

  • 0 in reply to RJ Hopper
    Prodigy 180 points

    Hi, 

    Thanks for your help.

    Where is the Low IF exactly ? The Low IF BPF at the output of IQ modulator or using the LPF of AFE7071 ?

    BR,

    XL

  • 0 in reply to XIN LI
    TI__Mastermind 18095 points

    The AFE707x supports a BB bandwidth up to 10 MHz.  You can opt to put your low BW signal anywhere in that range, say 5 MHz offset, which will give you separation from the carrier leakage and unwanted sideband.

    --RJH

  • 0 in reply to RJ Hopper
    Prodigy 180 points

    Thanks a lot !