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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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