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VCA2615: VPP specification

AnBer
Mastermind 29320 points
Part Number: VCA2615
Other Parts Discussed in Thread: VCA2617

Team,

Could you please clarify the below?

VCA261x are differential amplifers:

-VCA2617 specifies both the single ended and differential Maximum Input Voltage specification (see page 3 of SBOS326).

-For VCA2615 only one Maximum Input Voltage specification is given (see page 3 of  SBOS316D).
Is it single ended of differential?

Thanks in advance,

A.

  • 0
    TI__Genius 12025 points
    Hi A.,
    According to the VCA2615 data sheet's spec (ELECTRICAL CHARACTERISTICS) saying,
    "the input to the preamp (LNP) is single-ended;"
    then "Maximum Input Voltage" specification (for LNP) should be single-ended.

    Thank you!
    Have a nice day!

    Best regards,
    Chen
  • 0 in reply to Chen Kung
    Prodigy 220 points

    Hi Chen,

    Shall I assume that your answer also applies to output and input refered noise curve (fig 17 and 18)?

    Noise density have to be considered as single ended measurement?

    Different question:

    - which consideration/parameter let TI state that this device is "Suitable for 10-Bit and 12-Bit Systems" ?

    Regards,

    Pierre

  • 0 in reply to Pierre Lieutaud
    TI__Genius 12025 points

    Hi Pierre,

    How are you?

    Please take a look at the following 2 plots (one is from the VCA2615 data sheet,

    the other one is from the VCA2615 user's guide).

    briefly speaking, these two plots show the same thing:

    Input signal is single-ended to LNP input pin (LNP_IN+ only).

    VGA generates the differential output signals at these two both pins (VCA_out+ and VCA_out1-).

    1) from the VCA2615 Data Sheet:

    2) From the VCA2615 User's Guide:

    Therefore the Noise density should be calculated (for Input-referred Noise => by LNP single-ended input + VGA input

    and for output-referred Noise=> by VGA differential output).

    Thank you!

    Best regards,

    Chen

  • 0 in reply to Pierre Lieutaud
    TI__Genius 12025 points
    Hi Pierre,
    How are you?
    Thanks for using VCA2615 device.
    For your concern about saying:
    this device is "Suitable for 10-Bit and 12-Bit Systems"
    That is because for example,
    while Vcntl is used to increase the Gain
    at the same time the output Noise would be increased as well.
    Therefore for the overall system conditions,
    the VCA2615 data sheet explains it suitable for 10-bit (needs very high Gain)
    and 12-bit (needs middle Gain) system.

    Thank you very much!
    Have a nice day!

    Best regards,
    Chen
  • 0 in reply to Chen Kung
    TI__Genius 12025 points
    Hi Pierre,

    VCA2615 has both LNP and VGA structures together inside the device.
    Total two inside one VCA2615.
    Please take a look:
    (Note: the LNP circuitry has single-ended input and differential output
    VGA circuitry has differential input and differential output)


    And VCA2617 has only VGA inside the device.
    Total two VGAs inside one VCA2617.
    Please take a look:
    (Note: this VGA circuitry has differential input and differential output)


    Thank you!
    Have a nice day!

    Best regards,
    Chen
  • 0 in reply to Chen Kung
    Prodigy 220 points

    Hi Chen,

    Got it.

    The SNR of the device decreases while the gain increases.

    Regards,

    Pierre

  • 0 in reply to Pierre Lieutaud
    Prodigy 220 points
    Hi Chen,

    One way to improve the SNR would be to use band pass filtering, right?
    Instead of using the whole 50MHz bandwith of the device, only limit the bandwith to the usefull signal of my system.

    I'm aware of the VCA2617 but in our systems, we use LNA.
    Usually, we use very low noise OP AMPS in front of the VCA.
    Embedded LNA could be an option.

    Regards,

    Pierre
  • 0 in reply to Pierre Lieutaud
    TI__Genius 12025 points
    Hi Pierre,

    How are you?
    Yes, you are right.
    You can add the differential filter between VCA2617 VCA's outputs and your next device's inputs.
    Then you can improve the VCA2617's SNR performance for your application.

    Thank you!
    Happy New Year!

    Best regards,
    Chen
  • 0 in reply to Chen Kung
    Prodigy 220 points

    Thanks Chen,

    Happy new year to you too.

    Regards,

    Pierre