Before you can make a 1kHz sinewave oscillator with constant output level and better than 120dB harmonic distortion you'll need an
oscillator which does better than that when it passes through the required output level.
The circuit below was simulated in LTSpice 24.1.0 with all updates.
There are reasons why I'm not sure I'd trust version 17.x of LTSpice to give the most accurate results but I haven't tested this
circuit in any other version.
After starting the simulation, wait until it has simulated about 7 seconds and then stop the simulation. Close the annoying log
window which 24.1.0 will produce.
You can now select a sample of about 100ms when it passes through 0dB (just under 2V) and run an FFT on it with Blackman-Harris
window.
This will show that this circuit is approaching 120dB down on harmonics.
So if you want to do better than that then you'll need an oscillator circuit which has better performance to begin with. You can
then add gain control for constant level.
I've not so far found an oscillator circuit in LTSpice with better harmonic distortion performance than this one.
You can, of course, try to use filtering to reduce the unwanted harmonics. Removing the first four harmonics produced by this
circuit will get it approaching 130dB but don't ask me how that would be measured in reality or what it would cost to do so even if
it can be measured.
On 24/01/2025 11:14 am, Edward Rawde wrote:
Before you can make a 1kHz sinewave oscillator with constant output level and better than 120dB harmonic distortion you'll need
an
oscillator which does better than that when it passes through the required output level.
This is obviously true. Why do you think you need to tell us about it?
This will show that this circuit is approaching 120dB down on harmonics.
So if you want to do better than that then you'll need an oscillator
circuit which has better performance to begin with. You can
then add gain control for constant level.
I've not so far found an oscillator circuit in LTSpice with better
harmonic distortion performance than this one.
You can, of course, try to use filtering to reduce the unwanted
harmonics. Removing the first four harmonics produced by this
circuit will get it approaching 130dB but don't ask me how that would be >measured in reality or what it would cost to do so even if
it can be measured.
Before you can make a 1kHz sinewave oscillator with constant output level and better than 120dB harmonic distortion you'll need an
oscillator which does better than that when it passes through the required output level.
The circuit below was simulated in LTSpice 24.1.0 with all updates.
There are reasons why I'm not sure I'd trust version 17.x of LTSpice to give the most accurate results but I haven't tested this
circuit in any other version.
After starting the simulation, wait until it has simulated about 7 seconds and then stop the simulation. Close the annoying log
window which 24.1.0 will produce.
You can now select a sample of about 100ms when it passes through 0dB (just under 2V) and run an FFT on it with Blackman-Harris
window.
This will show that this circuit is approaching 120dB down on harmonics.
So if you want to do better than that then you'll need an oscillator circuit which has better performance to begin with. You can
then add gain control for constant level.
I've not so far found an oscillator circuit in LTSpice with better harmonic distortion performance than this one.
You can, of course, try to use filtering to reduce the unwanted harmonics. Removing the first four harmonics produced by this
circuit will get it approaching 130dB but don't ask me how that would be measured in reality or what it would cost to do so even if
it can be measured.
"john larkin" <JL@gct.com> wrote in message news:jei7pjt2pc35osipchs2891gqtavk25a7k@4ax.com...
On Thu, 23 Jan 2025 19:14:24 -0500, "Edward Rawde"
<invalid@invalid.invalid> wrote:
Before you can make a 1kHz sinewave oscillator with constant output level and better than 120dB harmonic distortion you'll need
an
oscillator which does better than that when it passes through the required output level.
The circuit below was simulated in LTSpice 24.1.0 with all updates.
There are reasons why I'm not sure I'd trust version 17.x of LTSpice to give the most accurate results but I haven't tested this
circuit in any other version.
After starting the simulation, wait until it has simulated about 7 seconds and then stop the simulation. Close the annoying log
window which 24.1.0 will produce.
You can now select a sample of about 100ms when it passes through 0dB (just under 2V) and run an FFT on it with Blackman-Harris
window.
This will show that this circuit is approaching 120dB down on harmonics. >>>So if you want to do better than that then you'll need an oscillator circuit which has better performance to begin with. You can
then add gain control for constant level.
I've not so far found an oscillator circuit in LTSpice with better harmonic distortion performance than this one.
You can, of course, try to use filtering to reduce the unwanted harmonics. Removing the first four harmonics produced by this
circuit will get it approaching 130dB but don't ask me how that would be measured in reality or what it would cost to do so even
if
it can be measured.
Open LT Spice and make a 1 KHz sinewave voltage source. Run for 10
seconds and FFT. The 3rd harmonic is down 48 dB.
So Spicing low distortion oscillators might not be an exercize in
reality.
The following circuit was simulated in LTSpice 24.1.0 ...
On Thu, 23 Jan 2025 19:14:24 -0500, "Edward Rawde"
<invalid@invalid.invalid> wrote:
Before you can make a 1kHz sinewave oscillator with constant output level and better than 120dB harmonic distortion you'll need an
oscillator which does better than that when it passes through the required output level.
The circuit below was simulated in LTSpice 24.1.0 with all updates.
There are reasons why I'm not sure I'd trust version 17.x of LTSpice to give the most accurate results but I haven't tested this
circuit in any other version.
After starting the simulation, wait until it has simulated about 7 seconds and then stop the simulation. Close the annoying log
window which 24.1.0 will produce.
You can now select a sample of about 100ms when it passes through 0dB (just under 2V) and run an FFT on it with Blackman-Harris
window.
This will show that this circuit is approaching 120dB down on harmonics.
So if you want to do better than that then you'll need an oscillator circuit which has better performance to begin with. You can
then add gain control for constant level.
I've not so far found an oscillator circuit in LTSpice with better harmonic distortion performance than this one.
You can, of course, try to use filtering to reduce the unwanted harmonics. Removing the first four harmonics produced by this
circuit will get it approaching 130dB but don't ask me how that would be measured in reality or what it would cost to do so even
if
it can be measured.
Open LT Spice and make a 1 KHz sinewave voltage source. Run for 10
seconds and FFT. The 3rd harmonic is down 48 dB.
So Spicing low distortion oscillators might not be an exercize in
reality.
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vmv6ac$22ufe$1@dont-email.me...
On 24/01/2025 11:14 am, Edward Rawde wrote:
Before you can make a 1kHz sinewave oscillator with constant output level and better than 120dB harmonic distortion you'll need
an
oscillator which does better than that when it passes through the required output level.
This is obviously true. Why do you think you need to tell us about it?
You do make me laugh sometimes Bill.
Your circuit doesn't come anywhere close to 120dB but it does depend on which simulator you ask.
Adding a FET gain stabilizer to the circuit I posted seems to have negligible effect on the distortion.
So I'd concentrate on the oscillator distortion level rather than the gain controller contribution if I wanted to attempt better
than 120dB.
On 24/01/2025 5:02 pm, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vmv6ac$22ufe$1@dont-email.me...
On 24/01/2025 11:14 am, Edward Rawde wrote:
Before you can make a 1kHz sinewave oscillator with constant output level and better than 120dB harmonic distortion you'll need
an
oscillator which does better than that when it passes through the required output level.
This is obviously true. Why do you think you need to tell us about it?
You do make me laugh sometimes Bill.
Your circuit doesn't come anywhere close to 120dB but it does depend on which simulator you ask.
I never said it did.
I was looking for comments on the way the current mirrors might screw up the waveform. I didn't get any.
Adding a FET gain stabilizer to the circuit I posted seems to have negligible effect on the distortion.
Then you haven't looked at the current waveform going through the the FET.
So I'd concentrate on the oscillator distortion level rather than the gain controller contribution if I wanted to attempt better
than 120dB.
And you'd probably better dump LTSpice 24.1 - it has been claimed that it has a serious bug.
That might explain why your simulations of my circuit run a thousand times slower for you than they do for me and a couple of
other people.
--
Bill Sloman, Sydney
On 24/01/2025 5:02 pm, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vmv6ac$22ufe$1@dont-email.me...
On 24/01/2025 11:14 am, Edward Rawde wrote:
Before you can make a 1kHz sinewave oscillator with constant output level and better than 120dB harmonic distortion you'll need
an
oscillator which does better than that when it passes through the required output level.
This is obviously true. Why do you think you need to tell us about it?
You do make me laugh sometimes Bill.
Your circuit doesn't come anywhere close to 120dB but it does depend on which simulator you ask.
I never said it did. I was looking for comments on the way the current mirrors might screw up the waveform. I didn't get any.
Adding a FET gain stabilizer to the circuit I posted seems to have negligible effect on the distortion.
Then you haven't looked at the current waveform going through the the FET.
So I'd concentrate on the oscillator distortion level rather than the gain controller contribution if I wanted to attempt better
than 120dB.
And you'd probably better dump LTSpice 24.1 - it has been claimed that it has a serious bug. That might explain why your
simulations of my circuit run a thousand times slower for you than they do for me and a couple of other people.
--
Bill Sloman, Sydney
On 24/01/2025 5:02 pm, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vmv6ac$22ufe$1@dont-email.me...
On 24/01/2025 11:14 am, Edward Rawde wrote:
Before you can make a 1kHz sinewave oscillator with constant output level and better than 120dB harmonic distortion you'll need
an
oscillator which does better than that when it passes through the required output level.
This is obviously true. Why do you think you need to tell us about it?
You do make me laugh sometimes Bill.
Your circuit doesn't come anywhere close to 120dB but it does depend on which simulator you ask.
I never said it did. I was looking for comments on the way the current mirrors might screw up the waveform. I didn't get any.
Adding a FET gain stabilizer to the circuit I posted seems to have negligible effect on the distortion.
Then you haven't looked at the current waveform going through the the FET.
So I'd concentrate on the oscillator distortion level rather than the gain controller contribution if I wanted to attempt better
than 120dB.
And you'd probably better dump LTSpice 24.1 - it has been claimed that it has a serious bug. That might explain why your
simulations of my circuit run a thousand times slower for you than they do for me and a couple of other people.
On 24/01/2025 5:02 pm, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vmv6ac$22ufe$1@dont-email.me...
On 24/01/2025 11:14 am, Edward Rawde wrote:
Before you can make a 1kHz sinewave oscillator with constant output level and better than 120dB harmonic distortion you'll need
an
oscillator which does better than that when it passes through the required output level.
This is obviously true. Why do you think you need to tell us about it?
You do make me laugh sometimes Bill.
Your circuit doesn't come anywhere close to 120dB but it does depend on which simulator you ask.
I never said it did. I was looking for comments on the way the current mirrors might screw up the waveform. I didn't get any.
Adding a FET gain stabilizer to the circuit I posted seems to have negligible effect on the distortion.
Then you haven't looked at the current waveform going through the the FET.
So I'd concentrate on the oscillator distortion level rather than the gain controller contribution if I wanted to attempt better
than 120dB.
And you'd probably better dump LTSpice 24.1 - it has been claimed that it has a serious bug. That might explain why your
simulations of my circuit run a thousand times slower for you than they do for me and a couple of other people.
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vnck1i$295d5$1@dont-email.me...
On 24/01/2025 5:02 pm, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vmv6ac$22ufe$1@dont-email.me...
On 24/01/2025 11:14 am, Edward Rawde wrote:
Before you can make a 1kHz sinewave oscillator with constant output level and better than 120dB harmonic distortion you'll need
an
oscillator which does better than that when it passes through the required output level.
This is obviously true. Why do you think you need to tell us about it? >>>>
You do make me laugh sometimes Bill.
Your circuit doesn't come anywhere close to 120dB but it does depend on which simulator you ask.
I never said it did. I was looking for comments on the way the current mirrors might screw up the waveform. I didn't get any.
Adding a FET gain stabilizer to the circuit I posted seems to have negligible effect on the distortion.
Then you haven't looked at the current waveform going through the the FET. >>
So I'd concentrate on the oscillator distortion level rather than the gain controller contribution if I wanted to attempt better
than 120dB.
And you'd probably better dump LTSpice 24.1 - it has been claimed that it has a serious bug. That might explain why your
simulations of my circuit run a thousand times slower for you than they do for me and a couple of other people.
If U3 and U8 (LT1115) in your circuit are replaced with LT1678 then on my computer with LTSpice 24.1.1 and all component updates,
the simulation completes almost as fast as I can start it, at about 55 ms/s. A sample near 10s is not quite 60dB down at 3kHz and 5kHz and 70dB down at 7kHz, approaching 80dB down everywhere else.
The parasitic 23MHz signal has gone.
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vnck1i$295d5$1@dont-email.me...
On 24/01/2025 5:02 pm, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vmv6ac$22ufe$1@dont-email.me...
On 24/01/2025 11:14 am, Edward Rawde wrote:
Before you can make a 1kHz sinewave oscillator with constant output level and better than 120dB harmonic distortion you'll need
an
oscillator which does better than that when it passes through the required output level.
This is obviously true. Why do you think you need to tell us about it? >>>>
You do make me laugh sometimes Bill.
Your circuit doesn't come anywhere close to 120dB but it does depend on which simulator you ask.
I never said it did.
I never said you said it did.
Facts are still facts whether anyone says them or not.
I was looking for comments on the way the current mirrors might screw up the waveform. I didn't get any.
Adding a FET gain stabilizer to the circuit I posted seems to have negligible effect on the distortion.
Then you haven't looked at the current waveform going through the the FET.
But I have looked at the distortion level both with and without the FET stabilizer and I have not found any difference worth having
in an LTSpice simulation.
should be as small as possible.
Perhaps JL would like to elaborate on what he means by two FETs in anti-parallel. How would you drive the gate of the other FET?
So I'd concentrate on the oscillator distortion level rather than the gain controller contribution if I wanted to attempt better
than 120dB.
And you'd probably better dump LTSpice 24.1 - it has been claimed that it has a serious bug.
Could you please provide a reference to this claim.
Who has claimed that it has a serious bug and is there an online discussion anywhere?
Exactly what is this serious bug other than the fact that your circuit gets completely different results?
That might explain why your simulations of my circuit run a thousand times slower for you than they do for me and a couple of
other people.
There is obviously a big difference but I have not so far seen any evidence to confirm that it is a serious bug.
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