Need filter design TLO82 1Hz to 3MHz frequency range with the gain 10

[Rockzinstruz]

Hi...

I need the design of filter using TL082.The operating frequency range 1Hz to 3MHz with gain 10.but the band width of the op amp Wide bandwidth 4MHz mentioned in the datasheets. Is it possible to design the filter circuit?Plz help me.





Thanks.

 

[Winterstone]

Hi...

I need the design of filter using TL082.The operating frequency range 1Hz to 3MHz with gain 10.but the band width of the op amp Wide bandwidth 4MHz mentioned in the datasheets. Is it possible to design the filter circuit?Plz help me.
Thanks.

It would be helpful for us to know what kind of "filter": Lowpass, bandpass, highpass, notch, allpass ?
More than that, what means "operating range"? Tunable? Which order? Selectivity? Bandwidth?

 

[Rockzinstruz]

band pass filter .band width 4Mhz

 

[Winterstone]

band pass filter .band width 4Mhz

That means: You ask for a band pass (BW=4 MHz) in the operating range (your first posting) between 1Hz and 3 MHz.
Sounds a bit confusing, does it not?

 

[Rockzinstruz]

need the filter design ,which has to pass the signal in the frequency range of 1Hz to 3MHz with gain 10.

 

[Winterstone]

need the filter design ,which has to pass the signal in the frequency range of 1Hz to 3MHz with gain 10.

OK, this sounds better.
That means: You need a lowpass with a gain of 20 dB and cut-off of 3 MHz, right? (And the mentioned 4 MHz are a typing error or so?).
And what about sigmnals at 3.5 MHz or 4 MHz ? How much attenuation? This is necessary to fix the order of the filter.

 

[Rockzinstruz]

right ...cut-off frequency 3MHz of signal with 0 db attenuation

 

[Nigel Goodwin]

Perhaps you should try telling us EXACTLY what you're trying to do (and why), you don't seem to understand anything about filters or opamps.

You would NEVER use a bandpass filter from 1Hz to 3MHz - you would just use a lowpass at 3MHz, assuming there's any need for a filter in the first place? - there's no need to filter DC out.

You also wouldn't really use an opamp for a 3MHz filter, as it would be an expensive device, and probably not needed anyway.

 

[MrAl]

Hi,

If the op amp you have chosen only has a bandwidth of 4MHz then you can not use it for anything that requires a bandwidth of 3MHz with a gain of 10 because the limit for a 4MHz amplifier at a gain of 10 is 400kHz. That's even without considering other factors like slew rate.
If you have a low level signal you are working with you might get away with a 30MHz op amp. That's if you want to do it in one stage. If you can use two stages then you can split the gain between the two stages as the square root of 10. Since sqrt(10) equals 3.16 that means you'll need two op amps each with a bandwidth of 10MHz, and set the gain of each stage to 3.16 . To do this in a filter application, you could do part of the filtering in one stage and part in the other stage. You still have to check with the slew rate to make sure it will work with your level of output signal required.
If you can split the gain between four stages you can make the gain of each stage 1.78 and that would provide the overall gain you need too. Each op amp would then have to have a bandwidth of about 5 or 6MHz. Still have to see if the op amp slew rate is fast enough for your signal level though.

If you state your output signal level this would help determine a suitable op amp.

 

[Rockzinstruz]

Actually ,I need a opamp circuit which has to increase the voltage of wave forms square,sine,triangular from 2V to 15V.At the same time the opamp has to pass the signal in the frequency of 1Hz to 3MHz.

I built the amplifier circuit with gain of 15 using TL082,but it passes the signal upto 200KHz.After 200KHz it makes the attenuated output signal.this is my problem.

 

[MrAl]

Hi,

If you calculate the gain bandwidth product required for your app you can tell right away that an amplifier might not work in this app, at least in a single stage.

I see the data sheet for the TL082 as spec'ing a GBW (gain bandwidth) of 3MHz, not 4MHz. That means with a gain of 1 we might be able to pass a sine signal at 3MHz assuming the output amplitude is not too high (less than 0.7 volts peak). But a gain of 1 doesnt help at all here, and an output of 0.7 volts certainly doesnt help either.

Also, with a gain of 7 and an output of 14v peak the TL082 bandwidth would be limited to about 150kHz, so yes it will attenuate after that.

So what does it take...

To get a gain of 7 at 3MHz and produce a sine signal at the output that goes up to 14v peak we would need an op amp that has a minimum gain bandwidth of 21MHz, and a slew rate minimum of 264 volts per microsecond. That's to do it all in one op amp section.

But that is just the op amp specification to handle a sine wave. Luckily, the triangle wave has a rate of rise with time less than the max for the sine wave, so we'd be covered for the triangle wave too.

However, now we come to the square wave. An ideal square wave has to have a rise time that is infinitesimal, and that is impossible to reproduce. Going slightly non ideal, we can use a rise and fall time that is just much faster than the pulse width. If we agree that a rise and fall time of one-tenth of the pulse width is good enough at the max frequency of operation, then the rise time has to be 33ns. To rise to 14 volts in 33ns we would need an op amp that has a slew rate of at least 420 volts per microsecond.
However, that's not the best way to do it. The best way would be to use a different circuit for the square wave and use a transistor output stage like maybe a MOSFET. The op amp would handle the sine and triangle, and the transistor(s) would handle the square wave output.

 

[Winterstone]

Actually ,I need a opamp circuit which has to increase the voltage of wave forms square,sine,triangular from 2V to 15V.At the same time the opamp has to pass the signal in the frequency of 1Hz to 3MHz.
I built the amplifier circuit with gain of 15 using TL082,but it passes the signal upto 200KHz.After 200KHz it makes the attenuated output signal.this is my problem.

OK, from the above I derive that you do not need a filter but simply an amplifier that has a gain of approx. 7.5 for frequencies up to 3 MHz.
Is this the only requirement ? Or are there some other restrictions regarding attenuation beyond 3 MHz?

 

[Rockzinstruz]

Ok..I've one doubt.That 21MHz bandwidth opamp.Is it suitable for low frequency signal? I mean will the amplifier circuit allows to pass the Hz range of frequency signal?

 

[Rockzinstruz]

Hi,

If you calculate the gain bandwidth product required for your app you can tell right away that an amplifier might not work in this app, at least in a single stage.

I see the data sheet for the TL082 as spec'ing a GBW (gain bandwidth) of 3MHz, not 4MHz. That means with a gain of 1 we might be able to pass a sine signal at 3MHz assuming the output amplitude is not too high (less than 0.7 volts peak). But a gain of 1 doesnt help at all here, and an output of 0.7 volts certainly doesnt help either.

Also, with a gain of 7 and an output of 14v peak the TL082 bandwidth would be limited to about 150kHz, so yes it will attenuate after that.

So what does it take...

To get a gain of 7 at 3MHz and produce a sine signal a the output that goes up to 14v peak we would need an op amp that has a minimum gain bandwidth of 21MHz, and a slew rate minimum of 264 volts per microsecond. That's to do it all in one op amp section.

But that is just the op amp specification to handle a sine wave. Luckily, the triangle wave has a rate of rise with time less than the max for the sine wave, so we'd be covered for the triangle wave too.

However, now we come to the square wave. An ideal square wave has to have a rise time that is infinite, and that is impossible to reproduce. Going slightly non ideal, we can use a rise and fall time that is just much faster than the pulse width. If we agree that a rise and fall time of one-tenth of the pulse width is good enough at the max frequency of operation, then the rise time has to be 33ns. To rise to 14 volts in 33ns we would need an op amp that has a slew rate of at least 420 volts per microsecond.
However, that's not the best way to do it. The best way would be to use a different circuit for the square wave and use a transistor output stage like maybe a MOSFET. The op amp would handle the sine and triangle, and the transistor(s) would handle the square wave output.

Okay..Now I understood this problem.Thanks for your replies Mr.MrAl.

 

[unclejed613]

you will need an op amp with a unity gain bandwidth of at least 30Mhz to amplify a 3Mhz signal with a gain of 10. unity gain bandwidth is also known as Gain-Bandwidth Product (which means you MULTIPLY the operating frequency by the gain required to find the required unity gain bandwidth). a TL082 or 072 will not work for this. two TLE2072 op amps cascaded with a gain of 3.16 might work, but the second stage's slew rate will be a limiting factor and you will end up severely distorting the signal.

 

[MrAl]

Hi,

You're welcome. BTW, i had to edit the section you quoted because i had mistyped the rise time as being "infinite" instead of "infinitesimal". Obviously the rise time has to be very fast not infinite <big chuckle here>

 

[unclejed613]

rise time IS very finite.... when i was in Army calibration school we had to measure the rise time of a tunnel diode pulse generator. it was supposed to be about 25pS. one of the tunnel diode pulsers had a problem and the best it would do for rise time was about 5nS.... and it changed a lot as well. the fastest an op amp can do for rise time will be determined by it's slew rate (usually measured in volts per microsecond). and some op amps don't have equal positive-going and negative-going slew rates.

 

[MrAl]

Hi,

Yes rise time is very finite in the real world, but in the theoretical world (which i referred to clearly in my other post) it can be infinitesimal. What i had typed wrong was that the rise time could be infinite. Clearly if the rise time was infinite it would take forever to move 1 volt (ha ha). It was supposed to read "infinitesimal" because a theoretical square wave has no rise or fall time. It if is down at t=0 and it goes up right after that, it goes up at t=0+ and there is no real number that can express that because it is just not there

 

[Rockzinstruz]

you will need an op amp with a unity gain bandwidth of at least 30Mhz to amplify a 3Mhz signal with a gain of 10. unity gain bandwidth is also known as Gain-Bandwidth Product (which means you MULTIPLY the operating frequency by the gain required to find the required unity gain bandwidth). a TL082 or 072 will not work for this. two TLE2072 op amps cascaded with a gain of 3.16 might work, but the second stage's slew rate will be a limiting factor and you will end up severely distorting the signal.

Mr.Unclejed613 , I tried amplifier circuits with TL082CP and I faced the frequency response problem with gain 1 also.
But here have one doubt.In the datasheet of TL082CP is mentioned wide bandwidth 4MHz with condition of Vs=+/- 15V ,Ambient temperature=25 celcius.
I tried the amplifier design with different gain values from 1 to 10.but I didnt get the 4MHz band width response even anyone gain value.So that I confused then, why mentioned wide band width range in the datasheet?I need clarification.


Thanks.

 

[unclejed613]

you won't get any gain at 4Mhz (the data sheet says 3Mhz is the unity gain bandwidth), and the slew rate limiting will only allow very small signals at that frequency. why are you still trying this with TL082 op amps after all you've been told about bandwidth limitations? you really need an op amp with 30Mhz bandwidth for what you are trying to do.