• State
  • Locked Locked
  • Replies 3 replies
  • Subscribers 49 subscribers
  • Views 1124 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.

OPA1641 & THS4601 GBW for SVF

Temmy Soesanto
Prodigy 40 points
Other Parts Discussed in Thread: OPA1641, OPA827, LME49860, THS4601

Hi,

I have seen in one post about minimum GBW for a filter, right now I have an audio filter project base on state variable filter using LME49860 & OPA1641 or OPA827 with:

F: 665Hz - 30475Hz

Q:  0.7 - 3.3

Integrator Gain: 5

but from the post http://e2e.ti.com/support/amplifiers/etc_amplifiers__other_linear/f/18/t/164098.aspx

minimum GBW requirement is so high and OPA1641 or OPA827 for the integrator  is not suitable?

And after the search THS4601 looks like a promising replacement but not designed for audio.

Can someone confirm that the calculation for GBW is valid for my application?

TI Tina tsc is attached.

Thank You.

SVF Filter.TSC
  • 0
    TI__Guru**** 189399 points

    Hi, Temmy,

    I am going to move your post to the Precision Amplifier forum where the op amp people hang out.

    -d2

  • 0 in reply to Don Dapkus
    Prodigy 40 points

    Hi Don,

    Thank You for taking care my post.

    Temmy

  • 0
    TI__Guru* 93105 points

    Hello Temmy,

    I haven't seen anything written about the amplifier gain-bandwidth needed for a state variable filter, but I expect that it is similar to the GBW requirements for the more common Sallen-Key and Multiple Feedback topologies. You would want to use the worst case requirements; the highest Q, highest frequency, and highest gain for determining the GBW.

    Using the formula presented in the other E2E forum post:

    GBW(min) = Fn x Q x ACL x 100

    The GBW(min) for your application would be:

    GBW(min) = (30475 x 3.3 x 5 x 100) = 50 MHz

    Note that this is a conservative estimation of the GBW. You may find that amplifiers having somewhat lower GBW work satisfactorily in the application. The LME49860 would be a fine choice, but the OPA827 and OPA1641 would have too low of GBW. The bandwidth of the THS4601 is in excess of what is needed.

    Actually, I expect there may be some leeway regarding the GBW requirement of the individual stages in a state variable filter. It would depend on the bandwidth, gain and Q that each individual amplifier is serving in the filter. It would be a matter of  the calculating the GBW(min) for each stage and selecting an amplifier that supports it.

    Regards, Thomas

    PA - Linear Applications Engineering