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

[MrAl]

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.

Hi again,


Even with an op amp with 4MHz unity gain bandwidth you can only get an output of roughly 0.7v peak at 4MHz. You need 20 times that so that op amp will NEVER work.

You have to get one point straight here...just because you buy an op amp with gain bandwidth of 3MHz doesnt mean that you can use that op amp at 3Mhz. If your OUTPUT signal goes OVER 0.7 volts peak with this op amp (that is less than one volt) then the op amp STILL limits the frequency response to less than 3MHz.

So the op amp behavior is limited by two most important things, not just the advertised bandwidth, but also by what is called the "Slew Rate".

So the two things you have to consider for a design are:
1. Bandwidth
2. Slew Rate

If you do not consider BOTH of these things the design probably will not work. In the case of a 3MHz bandwidth and a 3MHz signal and a 15v peak output it will definitely NOT work.

The gain bandwidth limits the usable BANDWIDTH right from the start, you cant use too high of a frequency because of that alone.

The slew rate limits the maximum peak output at a given frequency, but because it depends on frequency this too also limits the usable BANDWIDTH indirectly. To calculate the maximum peak output knowing the slew rate in volts per second we can use this:
PeakAmplitude=SlewRate/(2*pi*Frequency)
The PeakAmplitude here is in volts peak and the SlewRate in volts per second and Frequency in Hertz.

So for a slew rate of 13 volts per microsecond (which is 13e6 volts per second) and a frequency of 3Mhz we have:
PeakAmplitude=13e6/(2*pi*3e6)=0.69 volts peak.
This means the maximum output we can get from this op amp is about 0.7 volts even if the gain is only 1 when the frequency is 3MHz. We may not even get that if the op amp slew is actually somewhat below 13v/us.

We can use this to calculate what slew rate we really need then, as a minimum. Starting with:
PeakAmplitude=SlewRate/(2*pi*Frequency)

and solving for the SlewRate we get:
SlewRate=PeakAmplitude*2*pi*Frequency

Now using 15v as the peak amplitude and 3MHz as the frequency, we get a slew rate of 282.74e6 volts per second which is about 283 volts per microsecond, which helps us determine what op amp we need to find.

Next, knowing that we need a gain of 7.5 at a frequency of 3MHz we multiply 7.5 times 3000000 and we get 22.5Mhz as the required gain bandwidth produce for the op amp.

So taking these TWO things into account, we need an op amp with a gain bandwidth of 22.5Mhz and a slew rate of at least 283v/us.

So you see we had to consider TWO things in order to select an op amp, not just one thing.

There is also a third thing that limits the output swing. That's the output stage of the op amp. Many op amps can not put out a voltage that reaches as high as the positive supply rail or as low as the negative supply rail. There could be as much as 1.5v difference or maybe even more. That means if we want a plus and minus 15v output we may have to use a supply voltage that is actually plus and minus 17v or more. The output stage drops some voltage so we loose part of the power supply voltage just for that.
This specification is usually mentioned somewhere on the data sheet too.
A rail to rail output op amp can get closer to the actual supply rails though, but the load current has to be limited sometimes.

 

[unclejed613]

also, you keep quoting a GBW of 4Mhz, but the data sheet clearly says 3Mhz..... what manufacturer is the source of your data sheet? i'm using TI's data sheet. TI is the originator of the chip design, and all other manufacturers have licensed the chip masks and process from TI. this means that all TL082 chips are made the same way, and should have the same characteristics. if you have a data sheet that says 4Mhz, then i suspect that company let some marketing or sales guy add a fudge factor to the data....

 

[Rockzinstruz]

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.

For that I searched high bandwidth op amp.I found two op amp AD811 and THS 4051(THS 4051-U only mentioned in my another link).I had seen the datasheets of these two op amp. I dont have good source for getting components.So that I'm waiting for this.In between duration Iam doing my task with TL082.Soon I will get op amp.
I wants to make the schmitt trigger circuit from the same op amp which one is used as the amplifier part also.
Please suggest anyother good high bandwidth op amp for my requirement.It has to be easily work in practical implementation.



Thanks.

 

[Rockzinstruz]

also, you keep quoting a GBW of 4Mhz, but the data sheet clearly says 3Mhz..... what manufacturer is the source of your data sheet? i'm using TI's data sheet. TI is the originator of the chip design, and all other manufacturers have licensed the chip masks and process from TI. this means that all TL082 chips are made the same way, and should have the same characteristics. if you have a data sheet that says 4Mhz, then i suspect that company let some marketing or sales guy add a fudge factor to the data....

I reffered National semiconductor datasheet.

 

[Rockzinstruz]

Hi again,


Even with an op amp with 4MHz unity gain bandwidth you can only get an output of roughly 0.7v peak at 4MHz. You need 20 times that so that op amp will NEVER work.

You have to get one point straight here...just because you buy an op amp with gain bandwidth of 3MHz doesnt mean that you can use that op amp at 3Mhz. If your OUTPUT signal goes OVER 0.7 volts peak with this op amp (that is less than one volt) then the op amp STILL limits the frequency response to less than 3MHz.

So the op amp behavior is limited by two most important things, not just the advertised bandwidth, but also by what is called the "Slew Rate".

So the two things you have to consider for a design are:
1. Bandwidth
2. Slew Rate

If you do not consider BOTH of these things the design probably will not work. In the case of a 3MHz bandwidth and a 3MHz signal and a 15v peak output it will definitely NOT work.

The gain bandwidth limits the usable BANDWIDTH right from the start, you cant use too high of a frequency because of that alone.

The slew rate limits the maximum peak output at a given frequency, but because it depends on frequency this too also limits the usable BANDWIDTH indirectly. To calculate the maximum peak output knowing the slew rate in volts per second we can use this:
PeakAmplitude=SlewRate/(2*pi*Frequency)
The PeakAmplitude here is in volts peak and the SlewRate in volts per second and Frequency in Hertz.

So for a slew rate of 13 volts per microsecond (which is 13e6 volts per second) and a frequency of 3Mhz we have:
PeakAmplitude=13e6/(2*pi*3e6)=0.69 volts peak.
This means the maximum output we can get from this op amp is about 0.7 volts even if the gain is only 1 when the frequency is 3MHz. We may not even get that if the op amp slew is actually somewhat below 13v/us.

We can use this to calculate what slew rate we really need then, as a minimum. Starting with:
PeakAmplitude=SlewRate/(2*pi*Frequency)

and solving for the SlewRate we get:
SlewRate=PeakAmplitude*2*pi*Frequency

Now using 15v as the peak amplitude and 3MHz as the frequency, we get a slew rate of 282.74e6 volts per second which is about 283 volts per microsecond, which helps us determine what op amp we need to find.

Next, knowing that we need a gain of 7.5 at a frequency of 3MHz we multiply 7.5 times 3000000 and we get 22.5Mhz as the required gain bandwidth produce for the op amp.

So taking these TWO things into account, we need an op amp with a gain bandwidth of 22.5Mhz and a slew rate of at least 283v/us.

So you see we had to consider TWO things in order to select an op amp, not just one thing.

There is also a third thing that limits the output swing. That's the output stage of the op amp. Many op amps can not put out a voltage that reaches as high as the positive supply rail or as low as the negative supply rail. There could be as much as 1.5v difference or maybe even more. That means if we want a plus and minus 15v output we may have to use a supply voltage that is actually plus and minus 17v or more. The output stage drops some voltage so we loose part of the power supply voltage just for that.
This specification is usually mentioned somewhere on the data sheet too.
A rail to rail output op amp can get closer to the actual supply rails though, but the load current has to be limited sometimes.

Thanks for your explanation Mr.MrAl.

The third thing,supply voltage consideration on output voltage.
Previously I tried with TL082 ,got the output voltage 25Vp-p with gain 15 at 10KHz frequency with postive clipped waveform of sine and triangular wave.
But in the datasheet of TL082 mentioned the output voltage swing 13.5V at +/-15 supply voltage(Referred TL082 from National semiconductor datasheet).I little confused in this.Is not a good way to obtain the output voltage more than the supply voltage?


Thanks.

 

[Rockzinstruz]

Hi again,


Even with an op amp with 4MHz unity gain bandwidth you can only get an output of roughly 0.7v peak at 4MHz. You need 20 times that so that op amp will NEVER work.

You have to get one point straight here...just because you buy an op amp with gain bandwidth of 3MHz doesnt mean that you can use that op amp at 3Mhz. If your OUTPUT signal goes OVER 0.7 volts peak with this op amp (that is less than one volt) then the op amp STILL limits the frequency response to less than 3MHz.

So the op amp behavior is limited by two most important things, not just the advertised bandwidth, but also by what is called the "Slew Rate".

So the two things you have to consider for a design are:
1. Bandwidth
2. Slew Rate

If you do not consider BOTH of these things the design probably will not work. In the case of a 3MHz bandwidth and a 3MHz signal and a 15v peak output it will definitely NOT work.

The gain bandwidth limits the usable BANDWIDTH right from the start, you cant use too high of a frequency because of that alone.

The slew rate limits the maximum peak output at a given frequency, but because it depends on frequency this too also limits the usable BANDWIDTH indirectly. To calculate the maximum peak output knowing the slew rate in volts per second we can use this:
PeakAmplitude=SlewRate/(2*pi*Frequency)
The PeakAmplitude here is in volts peak and the SlewRate in volts per second and Frequency in Hertz.

So for a slew rate of 13 volts per microsecond (which is 13e6 volts per second) and a frequency of 3Mhz we have:
PeakAmplitude=13e6/(2*pi*3e6)=0.69 volts peak.
This means the maximum output we can get from this op amp is about 0.7 volts even if the gain is only 1 when the frequency is 3MHz. We may not even get that if the op amp slew is actually somewhat below 13v/us.

We can use this to calculate what slew rate we really need then, as a minimum. Starting with:
PeakAmplitude=SlewRate/(2*pi*Frequency)

and solving for the SlewRate we get:
SlewRate=PeakAmplitude*2*pi*Frequency

Now using 15v as the peak amplitude and 3MHz as the frequency, we get a slew rate of 282.74e6 volts per second which is about 283 volts per microsecond, which helps us determine what op amp we need to find.

Next, knowing that we need a gain of 7.5 at a frequency of 3MHz we multiply 7.5 times 3000000 and we get 22.5Mhz as the required gain bandwidth produce for the op amp.

So taking these TWO things into account, we need an op amp with a gain bandwidth of 22.5Mhz and a slew rate of at least 283v/us.

So you see we had to consider TWO things in order to select an op amp, not just one thing.

There is also a third thing that limits the output swing. That's the output stage of the op amp. Many op amps can not put out a voltage that reaches as high as the positive supply rail or as low as the negative supply rail. There could be as much as 1.5v difference or maybe even more. That means if we want a plus and minus 15v output we may have to use a supply voltage that is actually plus and minus 17v or more. The output stage drops some voltage so we loose part of the power supply voltage just for that.
This specification is usually mentioned somewhere on the data sheet too.
A rail to rail output op amp can get closer to the actual supply rails though, but the load current has to be limited sometimes.

I found AD811 Video amplifier.In this datasheet 140 MHz bandwidth at gain 1 and slew rate 2500V/us.
According to the Peak amplitude calculation,I calculated slewrate and bandwidth values for my spec.I need the slewrate 376.7V/us and bandwidth 30MHz.

But in this datasheet it mentioned 35MHz bandwidth at Gain 2.
Is this satisfy for my requirements ,Is it suitable or not?Plz explain this.


Thanks.

 

[Winterstone]

But in this datasheet it mentioned 35MHz bandwidth at Gain 2.
Is this satisfy for my requirements ,Is it suitable or not?Plz explain this.

When you read the data sheet carefully, you will see that the 3-dB bandwidth for a gain of 2 is given with 120 MHz.
The other value (35 MHz) applies to another specification (gain drop of only 0.1 dB rather than 3 dB).

 

[Rockzinstruz]

Thanks to all ' Electrotech on line' people.
As per all your ideas and suggestions I designed the amplifier part which is suitable for high frequency.For that I selected AD811 opamp.




With thanks,
Rockzinstruz

 

[Rockzinstruz]

Hi.....

I am going to design the input amplifier for the PIC microcontroller.
The circuit has to produce the 3.5 to 4 V square wave at the input of 2V sine /triangular/Square wave without any frequency changes between input and output wave forms and It has to work from 10Hz to 3 MHz frequency range.
Please Convey all your ideas related on this topic.



With thanks,
Rockzinstruz

 

[unclejed613]

use a schmitt trigger like a 74LS14 (you can substitute whatever appropriate TTL family you want for the "LS").

 

[Rockzinstruz]

use a schmitt trigger like a 74LS14 (you can substitute whatever appropriate TTL family you want for the "LS").

I built the 74LS14 schmitt trigger circuit and obtained the square wave output at the input of sine,triangular & square waveforms.But while varying the frequency from Hz to MHz range ,some changes occurs in output wave form shape and the frequency also.
Can we use the single schmitt trigger design for various frequency range?

 

[unclejed613]

are you looking at the output of the schmitt trigger with just an oscope (essentially open circuit) or with a terminating resistor (usually 470 ohms from the output to ground). what type of construction are you using? a plug-in breadboard doesn't work well above 500khz or so. there are many things that can mess up the waveforms. a schematic of what you have built would be helpful.

 

[Rockzinstruz]

I am making a circuit in bread board connections