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LMH6559: LMH6559 circuit structure

Part Number: LMH6559
Other Parts Discussed in Thread: OPA656, OPA2837

Hello everyone

I use LMH6559  to assure that the excitation signals have low impedance.But refer to LMH6559 datasheet ,I still can't determine the circuit structure. I hope you can give me some suggestions. Thank you.

The following is my confusion and the current design of the circuit.  

                                                       Fig 1.  The  current design of circuit

                                                  Resister value of  R5

                                                     Fig2 DC simulation results

confusion:  (1) LMH6559 is a close loop buffer so it does not require any external components ? So, can I use the above circuit structure ?

                                                   Fig3 Use one buffer to drive one transmission line

                   (2)Why is the voltage simulation negative? How can I turn the voltage into a positive value?

                   (3)If the above circuit structure is wrong,then how should I design it with the above component .(LMH6559 OPA656)

                       And refer to the datasheet,how do I choose the value of  R and C (input and output).

                                            Fig 4.LMH6559 Typical Schematic

  • This sure looks confused

    1. The LMH6559 is a low output impedance voltage source - why are you using such large R's in the OPA656 - is this like a a test circuit for an eventual transimpedance design,

    2. When you switch to 100Mohm on the buffer input, it is going to go to the supply rail due to bias current times that 100Mohm, 

    If you want to switch between two sources, and the OPA2837 is fast enough, it handles wired or mux operations using the disable lines.