• State
  • Locked Locked
  • Replies 5 replies
  • Subscribers 50 subscribers
  • Views 211 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Original question:

MSP-EXP430FR2355: Interfacing confirmation

LMH5401: Clarification with the datasheet specifications and potential applicability

Jonathan Geronga
Expert 7930 points
Part Number: LMH5401

Hi Team,

Our customer would like to confirm if  LMH5401 can handle the bandwidth they need for their application with the questions below.

1. What is the true 3 dB small-signal bandwidth for the LMH5401 for a single-ended input and a differential output? Input signal levels are on the order of 6-60 nV/√Hz RMS?

2. What is the gain-bandwidth product for the maximum small-signal bandwidth?

3. Are there any performance issues beyond a 2 MHz bandwidth for small signals?

Please let me know if you have any questions for the customer.

Thanks,

Jonathan

  • 0
    Guru 47535 points

    Without a target gain, these cannot be answered - that is a pretty small signal, noise will be the main issue if this is a broadband app. 

  • 0 in reply to Michael Steffes
    Prodigy 120 points

    Michael Steffes said:

    Without a target gain, these cannot be answered - that is a pretty small signal, noise will be the main issue if this is a broadband app. 

    I'm not worried about the noise if your data sheet is correct. At least not just yet. 

    The game's pretty much over if I can't sustain the bandwidth, and that is a hard 6 GHz. The gain I need is what I can get at 6 GHz (as long as it's more than 1). My concerns now are as follows:

    1. Is there a minimum gain required for stable operation?

    2. Is the 3 dB bandwidth truly 6 GHz?

    3. What is the actual GBP for this part?

    Thanks

  • 0 in reply to Ash LAW
    Guru 47535 points

    So the 6GHz is at a signal gain of 4V/V or a noise gain of 5 about. Gain of 2 is the lowest gain shown in Figure 1, that is noise gain of 3witha bout 2.5dB peaking and 6GHz BW again. it probably would work at gain of 1, noise gain of about 2, but will be peaking more

    GBP is 8GHz but what you actually get over gains is very phase margin dependent, 

  • 0 in reply to Michael Steffes
    Prodigy 120 points

    Michael Steffes said:

    So the 6GHz is at a signal gain of 4V/V or a noise gain of 5 about. Gain of 2 is the lowest gain shown in Figure 1, that is noise gain of 3witha bout 2.5dB peaking and 6GHz BW again. it probably would work at gain of 1, noise gain of about 2, but will be peaking more

    GBP is 8GHz but what you actually get over gains is very phase margin dependent, 

    You have me thoroughly confused now, so I'm guessing there's some definition difference. If the bandwidth is 6 GHz at a gain of 4 I would say the GBP is 24 GHz. If the GBP is 8 GHz and the bandwidth is 6 GHz I'd say the max gain for 6 GHz BW is 8/6 = 1.333. So what am I missing?

    The noise gain isn't an issue because I'm actually trying to maintain a 6 dB SNR for the minimum signal levels, for which there is ample headroom if the input noise voltage and current are as spec'd. Even if that changes by about 3 dB I have enough headroom in my design.

    Do you have any specs on the phase characteristics when you talk about the "Phase Margin". 

    Thanks

  • 0 in reply to Ash LAW
    Guru 47535 points

    So this is a voltage feedback FDA

    GBP is a very simplified model that rarely applies to these higher speed parts, 

    Here is a recent detailed discussion of simulation loop phase margin, parts 6 to 8 then go through VFA, CFA, and FDA examples  - you want part 8

    https://www.planetanalog.com/stability-issues-for-high-speed-amplifiers-introductory-background-and-improved-analysis-insight-5/

    And then, since this gain bandwidth confusion is so pervasive I did this one later, 

    https://www.planetanalog.com/why-is-amplifier-gbp-so-confusing-insight-12/

    The references in these give you pointers to classic developments that were largely simplified (or in error).