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OPA692: OPA692

Richard Jenkins
Prodigy 30 points
Part Number: OPA692
Other Parts Discussed in Thread: THS3491

Tool/software:

Technical Support,

I'm considering using the OPA692 to split a pulsed signal, into two equal signals. However the supplies will be: 0 and 12V and the output pulsed signals are 0V(low) and 11V (high), all into 50ohm loads. Is this possible? Thanks

  • 0
    TI__Genius 16245 points

    Hi Richard,

    If the goal is to output a 0V to 11V signal, regardless of device, will not be possible as there are no amplifiers that can truly output 0V with a single supply configuration. You would have to apply a small negative supply to truly swing to 0V irrespective of device. However, for this device specifically, the output can swing ~1.3V from the rails. Meaning it can output 1.3V to 10.7V using a 0V to 12V rail.  One option would be to adjust your supplies to account for headroom concerns. The other option would be to use a rail-to-rail device which usually swing 100mV (or less) from the rails. You would still not swing to 0V but would be able to swing to 11V. However, most of our rail-to-rail output devices will not have the slew rate and bandwidth performance the OPA692 has. With everything mentioned you still need to consider the input-common-mode range of a given device, but this would depend on the configuration being used.

    Best Regards,

    Ignacio

  • 0
    Prodigy 30 points

    Thanks for your response. As mentioned I'm splitting a video signal 0 to 10V  into two paths in a  50ohm impedance system, similar to Fig 5 (datasheet) but with 50ohm resistors. For a gain of 2, would it provide a direct copy of the input pulsed signal. The power supplies are +12V and -1.3V and the input signal is 0 to 10V?

    Much appreciated.

    Richard

  • 0 in reply to Richard Jenkins
    TI__Genius 16245 points

    Hi Richard,

    I was able to look over the device with your requirements and I do not think this device would work. The recommended supply for this device is 12V. In order to not violate you common-mode input range, you would need a negative supply below -1.5V and to get 10V at the output of the amplifier you would also need above 11V, which would be a total supply greater than 12V. I would like to ask, for this application, is it one input going into two amplifier devices, where each drives a single 50-ohm resistive network, like Figure 5, or is the goal one amplifier driving two individual 50-ohm resistive networks? If it's the latter, one other consideration is the output current drive of the amplifier as it would be a max current of ~200mA the amplifier is outputting.

    Best Regards,

    Ignacio

  • 0 in reply to Ignacio Vazquez Lam1
    Prodigy 30 points

    I was going  for the fig 5 configuration.

    Would you recommend a different approach with this splitter network or a different device that would work. We have supplies of 12V and -5V and our pulsed signal is 0 to 10V (input) where we would like a copy of this at the output of at least one of the ports. The other output port can be half this voltage. The bandwidth would need to be >200MHz..

    Thanks

    Richard

  • 0 in reply to Richard Jenkins
    TI__Genius 16245 points

    Hi Richard,

    I will be looking through our portfolio and see if there is a device that could work with these supplies, however options might be limited. I would like to ask for the input signal can you share what the input is expected to be at the non-inverting pin. Is it a 0V to 10V signal going through 50-ohms which would be terminated at the input of this device? Meaning the signal at the non-inverting node will actually be 0V to 5V, which would then be gained up 2V/V to get 0V to 10V at the output? This will help get a common-mode input range to further filter through devices.

    Best Regards,

    Ignacio

  • 0 in reply to Ignacio Vazquez Lam1
    Prodigy 30 points

    Hi Ignacio,

    Yes it's 0 to 10V into a 50ohm system, so your description is correct: the non-inverting pin would be 0 to 5V, and 0 to 10V at the output.

    I presume the schematic would show a 50ohm resistor to ground at the input while, at the output, it would it would have 50ohms in series to the output port. The pulsed signal is a square wave with short rise time < 15ns, ideally 10ns.

  • 0 in reply to Richard Jenkins
    TI__Genius 16245 points

    Hi Richard,

    I was able to look through our portfolio and a device I believe will work for your application is the THS3491. This is a very fast device and might be a little overkill for your application, but our other devices either did not have enough headroom at the output or were not able to go beyond 12V supplies. For this device, you would need 12V and -5V supplies as the input range requires 4.1 from the rails, so to allow 0V input you would need -4.1V and below. This device has great slew rate performance, which would be needed to swing the output 10V in 10ns. It also has the output current required to drive a 100ohm load. We also have an EVM available for this device, which is recommended to ensure this device is performing as expected for your application.

    Best Regards,

    Ignacio