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From: "Edward Rawde" <invalid@invalid.invalid>
Newsgroups: sci.electronics.design
Subject: Re: Sinewave oscillator without gain control.
Date: Wed, 29 Jan 2025 15:35:17 -0500
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"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.

LTSpice 24.1.1 is now available.
The circuit below produces a 24mV pk-pk sineish wave at 23 MHz on my installation of LTSpice 24.1.1 with all component updates.
FFT shows 23 MHz at -40dB
Simulation speed is about 115 us/s
I didn't simulate beyond 2.5 ms

Simulation in LTSpice 24.0.12 shows pretty much identical behaviour but the simulation speed is slower at about 75us/s.

Version 4.1
SHEET 1 3608 920
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FLAG 16 -1520 Vout
FLAG -1088 -1504 Vee
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FLAG -624 -1472 Vcc
FLAG -208 -1584 Vcc
FLAG -608 -1328 Vee
FLAG -224 -1440 Vee
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WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 12
SYMBOL voltage -1136 -1776 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value 12
SYMBOL cap -448 -1600 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
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SYMATTR Value 15n
SYMATTR SpiceLine V=63 Rser=4 Lser=12n
SYMBOL res -448 -1568 R270
WINDOW 0 27 56 VTop 2
WINDOW 3 5 56 VBottom 2
SYMATTR InstName R4
SYMATTR Value 10.7k
SYMATTR SpiceLine tol=1
SYMBOL cap -64 -1728 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C6
SYMATTR Value 15n
SYMATTR SpiceLine V=63 Rser=4 Lser=12n
SYMBOL res -480 -1856 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R22
SYMATTR Value 2.49k
SYMATTR SpiceLine tol=1
SYMBOL cap -1248 -1952 R0
WINDOW 0 -60 15 Left 2
WINDOW 3 -62 54 Left 2
SYMATTR InstName C7
SYMATTR Value 100n
SYMBOL cap -1248 -1744 R0
WINDOW 0 -60 15 Left 2
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SYMATTR Value 100n
SYMBOL res -160 -1600 R270
WINDOW 0 27 56 VTop 2
WINDOW 3 5 56 VBottom 2
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SYMATTR SpiceLine tol=1
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WINDOW 0 0 56 VBottom 2
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SYMATTR Value 4.99k
SYMATTR SpiceLine tol=1
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WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
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SYMATTR Value 120
TEXT -1248 -1352 Left 2 !.tran 0 10s 0s startup