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LMH32401: LMH32401 transimpedance amplifier for high BW

Yorgos Stratakos
Prodigy 10 points
Part Number: LMH32401
Other Parts Discussed in Thread: OPA856, LMH34400

Tool/software:

I want to use the LMH32401 as a transimpedance amplifier with analog bandwidth of at least 250MHz. I prefer to have single ended output at 50 Ohms load. What is the most proper ciruitry I should use at the Out+ and Out- in order to get single output at 50 Ohms. What is the maximum output voltage level I can get at 50 Ohms ? I am going to implement the whole circuit on FR4 20mils thick material. Should I take special care on the bottom layer ground ? (e.g have ground voids beneath certain components in order to reduce parasitic capacitances. It would be also nice to provide me a TINA circuit model to test myself the behaviour of the proposed circuit.

Thanks,

Yorgos

  • 0
    TI__Prodigy 260 points

    Hi Yorgos, 

    Thanks for your interest in our integrated TIAs. 

    For differential to single ended conversion of LMH32401 output, consider a difference amplifier using the low noise unity gain stable OPA856. 

    The LMH32401 supports a total differential output swing of approximately 4Vpp at VOCM set to mid supply. 

    The OPA856 can support a single ended swing of approximately 2.5Vpp and can drive upto 80 mA of output current linearly. This would be sufficient to driving a 50 Ohms load. 

    We also have the LMH34400 which is an integrated TIA with single ended output with 40 kOhm transimpedance gain, can achieve 240MHz of bandwidth and can drive a 100 ohm load. 

    For Layout guidelines, please refer to the layout guidelines session of the datasheets of both LMH32401 and OPA856. If the lengths of the traces are long, please use matched transmission lines to reduce reflections. Its recommended to reduce the input capacitance at the inverting input pin by cutting out the ground plane below the traces connected to the inverting input. 

    The TINA models for both the LMH32401 and OPA856 are available at the product folder. 

    https://www.ti.com/product/LMH32401#design-tools-simulation

    https://www.ti.com/product/OPA856#design-tools-simulation

    Regards,

    Eldho