• State TI Thinks Resolved
  • Locked Locked
  • Replies 2 replies
  • Answers 1 answer
  • Subscribers 49 subscribers
  • Views 204 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.

BAND PASS FILTER PROJECT

Stas Kogan
Prodigy 125 points
Other Parts Discussed in Thread: OPA637

HI everyone,

I will be happy to get some help with a simulation from pspice project I am doing.

I assembled a scheme witch gives me gain of approx. 40DB 
My FL is approx.. 6KHZ and FH approx. 600KHZ.

But i have a problem that i nedd the slope at the ene to be -20db/dec and it is -40db/dec 

and my ROUT to be 13K ohm and it is 3Kohm.

the scheme is:

and the sym is



plese help me to find my mistake

much regards.

  • 0
    TI__Guru 51701 points

    Hi Stas,

    Stas Kogan said:
    But i have a problem that i nedd the slope at the ene to be -20db/dec and it is -40db/dec 
    Stas Kogan said:
    I assembled a scheme witch gives me gain of approx. 40DB 
    My FL is approx.. 6KHZ and FH approx. 600KHZ.

    Here is an option with OPA637 (using the op amp's BW for the attenuation at higher frequency), where the slope is approx. -20dB/decade. The zero is also rising at +20dB/dec.. The gain is 101 V/V. 

    OPA637 BPF 06192023.TSC

    I see that you are trying building your own op amp with LTSpice. The issues are that you may be able to simulate one, but you are going to have current matching and parasitic capacitance issues when you are trying to construct the circuit. It is going to have issues as you have observed.  

    If you want to simulate the mosfet op amp in LTSpice, you may have to use the NMOS4 to have the complete control of mosfet models, and take into account of all the parasitics, zeros and poles in the op amp. I am unable to support a customer with the LTSpice due to the competitor's license requirements.  Also, the cmos model seems to be operating in open loop configuration. 

    Below is the TI FilterPro tool online. You may configure your BPF using the tool, but the tool is typically used for higher order filter design, and you just want to have simple one order filter for your application or simulation. 

    https://webench.ti.com/filter-design-tool/filter-type

    If you have additional questions, please let me know. 

    Best,

    Raymond

  • 0 in reply to Raymond Zhang1
    TI__Guru 51701 points

    Hi Stas,

    I hope that your issues are resolved. To construct a discrete op amp circuit, you would need to verify the op amp has the required bandwidth. Since your gains are 100V/V and the filter has be operated up to 600kHz, you would need minimum 60MHz op amp BW for the filtering application (GBP or Gain Bandwidth Product). So I picked OPA637 to construct the filter application. 

    I am going to close this inquiry. If you have additional questions, please let us know. 

    Best,

    Raymond