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OPA859: Driving 1GHz on a coax cable with an OPA859 or BUF802

Bernard Harris70
Prodigy 100 points
Part Number: OPA859
Other Parts Discussed in Thread: BUF802,

Tool/software:

I need to drive a 1GHz signal on a 1m  50ohm coax cable and am considering either OPA859 or BUf802. The OPA859 is in unity gain configuration and is somewhat preferable due to lower input capacitance.

  1. Can both of these amplifiers directly drive a coax cable or is an additional  cable driving buffer preferable?
  2. Is there a need for series termination at the amplifier output? The cable is terminated into 50 Ohms at the far end.
  3. Is there a reference design with layout for driving a cable with low distortion at about 1GHz?

Thanks a lot

  • 0
    TI__Mastermind 25735 points

    Hello Bernard,

      I apologize for missing your thread. 

    1. There is no issue driving a meter long 50ohm coax cable, but it is very critical to match the source and load impedances especially for a 1GHz signal. At these lengths + speed, it would be considered a transmission line. Without impedance matching, signals will be partially reflected back and forth, interfering with incoming signals, until the cable is choppy and noisy. PCB traces should have a characteristic impedance of 50Ohms, and overall layout should be designed with care. A high power buffer is used if you need the high output current (high output signal or heavy load/driving high capacitance at high frequencies).
    2. Yes, this is an example:

      1. Source: www.ti.com/.../sloa046.pdf
    3. I am gathering these resources, and will get back to you by today on high speed layout and driving transmission lines. 

      Also, would you be able to share more details of your design/application to recommend the best suited amplifier?

    Thank you,
    Sima