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LMH6505 about clock

hisakichi kobayashi
Intellectual 950 points
Other Parts Discussed in Thread: LMH6505

hiall,

And AvMax=100V/V is usefull, see snosat4e.pdf and pabe 6 Fregaurecy
Rseponse for Various VG(AVMAV = 100) .
In a reference example, they are RF=2.32komega and RG=18ohm.

>RG=18ohm was not able to be chosen from Vin (MAX) regulation.
> 1) RG=180ohm from Vin(MAX) =0.9V.
> 2) AvMax = 100times it is RF=20komega.

Figure8 is 2.32komega f3dB=40 MHz.
From an inverse proportion rule, it is set to f3dB=4.64MHz by RF=20komega.
If there is no "feedback current to some extent, it will not operate normally." Although it is ,
How doesn't it operate?
Although it is not high bandwidth, may I think that it operates as 4 MHz of zones?

Regards,
Hisa Kobayashi.

 

  • 0
    TI__Mastermind 22825 points

    Hello Kobayashi-san,

    If I understand your question correctly.

    You like to operate the LMH6505 Variable Gain Amplifier at a gain of 100V/V but also like to increase the value of RG from the nominal 18ohm shown in Figure 8 for maximum input voltage condition of 0.9V (limited by IRG_Max = 5mA).

    I agree that the expected -3dB bandwidth should be close to 4.6MHz (from 40MHz with RF= 2.32k in Figure 8) or lower when you raise RF to ~20kohm. I say lower as, with this high value of RF, your output amplifier closed loop should approach a single pole (90 deg. phase margin) type response and speed may be lower than the ratio of feedback resistors may suggest. But, I agree in principle with your proposal to make sure you can accommodate and input of 0.9V maximum.

    Regards,

    Hooman