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Op amp not working out as planned

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Wimberleytech:

--- Quote ---Yes you have missed something: an anti-aliasing filter will theoretically give a pure sine wave, right up to half the sampling frequency. In practise, you'll probably be limited to less than half the sample rate, but it should be possible to get a much higher frequency, than 1MHz and still have a decent sine wave.


--- End quote ---

Did you mean "smoothing filter," and more specifically a "brick wall smoothing filter" would be the only way to get a pure sine up to half the sampling frequency?

StillTrying:
Here's another +/- 12V version. Simply driving the top end R1 in the above schem. with -1V to +8V allows for the 1.2Vpp output to be offset all -Ve, all +Ve or centered on 0V of course, which looks like that.

Amplitude is still fixed at 1.2Vpp, until someone comes up with a good simple idea. :)

LT .asc if someone wants to play with it.

Zero999:

--- Quote from: StillTrying on April 06, 2018, 12:43:10 am ---Here's another +/- 12V version. Simply driving the top end R1 in the above schem. with -1V to +8V allows for the 1.2Vpp output to be offset all -Ve, all +Ve or centered on 0V of course, which looks like that.

Amplitude is still fixed at 1.2Vpp, until someone comes up with a good simple idea. :)

LT .asc if someone wants to play with it.

--- End quote ---
Unfortunately the LT1022 is unsuitable for this application. It's over an order of magnitude too slow. Try a faster amplifier such as the AD818.


--- Quote from: netdudeuk on April 05, 2018, 11:10:47 am ---
The AD9833 has a VOUT Maximum of 0.65V and a VOUT Minimum of 38mV.

So, that's the peak input voltage.

Regarding the peak output voltage, here are the specifications for a branded budget 5MHz arbitrary function generator -

2mVpp~10Vpp (50?, ?10MHz)
4mVpp~20Vpp (high impedance, ?10MHz)

So, maybe something along these lines (Vpp and maximum frequency) looks sensible for my purpose, which is to have a signal generator to experiment with op amps (which I'm now actually doing), filters, etc ?

I'll not be putting the signal down long cables.

I understand that I'm going to have to put in more volts in if I want more volts out.

Thanks


--- End quote ---
What's your budget?

High speed amplifier ICs aren't cheap, especially ones suitable for running off the higher supply voltages required to give 20Vpp. The AD818 I just mentioned above seems to be the best value for money and meets your specification.

You'll need an anti-aliasing filter. I think a passive, LRC design might be the best option here, as it's tricky to design an active filter at these frequencies.

netdudeuk:

--- Quote from: Hero999 on April 06, 2018, 10:57:38 pm ---
--- Quote from: StillTrying on April 06, 2018, 12:43:10 am ---Here's another +/- 12V version. Simply driving the top end R1 in the above schem. with -1V to +8V allows for the 1.2Vpp output to be offset all -Ve, all +Ve or centered on 0V of course, which looks like that.

Amplitude is still fixed at 1.2Vpp, until someone comes up with a good simple idea. :)

LT .asc if someone wants to play with it.

--- End quote ---
Unfortunately the LT1022 is unsuitable for this application. It's over an order of magnitude too slow. Try a faster amplifier such as the AD818.


--- Quote from: netdudeuk on April 05, 2018, 11:10:47 am ---
The AD9833 has a VOUT Maximum of 0.65V and a VOUT Minimum of 38mV.

So, that's the peak input voltage.

Regarding the peak output voltage, here are the specifications for a branded budget 5MHz arbitrary function generator -

2mVpp~10Vpp (50?, ?10MHz)
4mVpp~20Vpp (high impedance, ?10MHz)

So, maybe something along these lines (Vpp and maximum frequency) looks sensible for my purpose, which is to have a signal generator to experiment with op amps (which I'm now actually doing), filters, etc ?

I'll not be putting the signal down long cables.

I understand that I'm going to have to put in more volts in if I want more volts out.

Thanks


--- End quote ---
What's your budget?

High speed amplifier ICs aren't cheap, especially ones suitable for running off the higher supply voltages required to give 20Vpp. The AD818 I just mentioned above seems to be the best value for money and meets your specification.

You'll need an anti-aliasing filter. I think a passive, LRC design might be the best option here, as it's tricky to design an active filter at these frequencies.

--- End quote ---

I've ordered a AD818 thanks.

netdudeuk:
I have the AD818 but TBH, I'm not sure to hook it up for this application.

Here's the data sheet -

http://www.analog.com/media/en/technical-documentation/data-sheets/AD818.pdf

Also, the data sheet states (gain ≥ 2, or gain ≤ –1).  Is this really the limit of how much it can boost the signal from the AD9833 ?

Thanks

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