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From: Bill Sloman <bill.sloman@ieee.org>
Newsgroups: sci.electronics.design
Subject: Re: Low distortion sinewave oscillator without big capacitor.
Date: Thu, 10 Apr 2025 20:37:03 +1000
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On 10/04/2025 6:01 am, john larkin wrote:
> On Wed, 9 Apr 2025 11:14:08 -0400, "Edward Rawde"
> <invalid@invalid.invalid> wrote:
> 
>> "Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vt60p8$q8qf$1@dont-email.me...
>>> On 9/04/2025 11:57 pm, Edward Rawde wrote:
>>>> "Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vt4se2$3qshb$1@dont-email.me...
>>>>> On 9/04/2025 1:56 am, Edward Rawde wrote:
>>>>>> "Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vt2bck$1gmbm$1@dont-email.me...
>>>>>>> On 7/04/2025 11:10 pm, Edward Rawde wrote:
>>>>>>>> "Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vsvspr$33gdd$1@dont-email.me...
>>>>>>>>> On 7/04/2025 3:25 am, Edward Rawde wrote:
>>>>>>>>>> "Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vsuacb$1d4ec$1@dont-email.me...
>>>>>>>>>>> On 7/04/2025 12:39 am, Edward Rawde wrote:
>>>>>>>>>>>> "Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vsu092$14oc7$1@dont-email.me...
>>>>>>>>>>>>> On 6/04/2025 2:12 am, JM wrote:
>>>>>>>>>>>>>> On Fri, 4 Apr 2025 23:55:11 -0400, "Edward Rawde"
>>>>>>>>>>>>>> <invalid@invalid.invalid> wrote:
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> "JM" <sunaecoNoChoppedPork@gmail.com> wrote in message news:uop0vjp3d13t441ujfboi5aeeg08anm1je@4ax.com...
>>>>>>>>>>>>>>>> On Fri, 4 Apr 2025 16:29:27 -0400, "Edward Rawde"
>>>>>>>>>>>>>>>> <invalid@invalid.invalid> wrote:
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>> "JM" <sunaecoNoChoppedPork@gmail.com> wrote in message news:add0vjdh2gcma0n9pfunq76n04cfbkhtnj@4ax.com...
>>>>>>>>>>>>>>>>>> On Fri, 4 Apr 2025 14:25:29 -0400, "Edward Rawde"
>>>>>>>>>>>>>>>>>> <invalid@invalid.invalid> wrote:
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>> "Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vsnufh$2ou7j$1@dont-email.me...
>>>>>>>>>>>>>>>>>>>> On 4/04/2025 11:33 am, JM wrote:
>>>>>>>>>>>>>>>>>>>>> On Thu, 3 Apr 2025 19:25:33 -0400, "Edward Rawde"
>>>>>>>>>>>>>>>>>>>>> <invalid@invalid.invalid> wrote:
>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>> "JM" <sunaecoNoChoppedPork@gmail.com> wrote in message news:qq8tujlpciqc2jrd0ibljmjr9pd37ip6hi@4ax.com...
>>>>>>>>>>>>>>>>>>>>>>> On Sun, 30 Mar 2025 14:54:56 -0400, "Edward Rawde"
>>>>>>>>>>>>>>>>>>>>>>> <invalid@invalid.invalid> wrote:
>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>> Not long ago JM posted a 1KHz sinewave oscillator with very low distortion.
>>>>>>>>>>>>>>>>>>>>>>>> It used a 470uF non polarized capacitor which in practice would probably be made from two 1000uF capacitors.
>>>>>>>>>>>>>>>>>>>>>>>> There's nothing wrong with that but I wanted to see whether I could make a working circuit without needing
>>>>>>>>>>>>>>>>>>>>>>>> such
>>>>>>>>>>>>>>>>>>>>>>>> a
>>>>>>>>>>>>>>>>>>>>>>>> large
>>>>>>>>>>>>>>>>>>>>>>>> capacitor.
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>> You will need to adjust the feedback to suit.  Start with a -5 or -6
>>>>>>>>>>>>>>>>>>>>> gain block after the integrator and adjust it's gain until the startup
>>>>>>>>>>>>>>>>>>>>> is clean (no saturation).
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>> Here's my version of John May's variation.
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>> ...
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>> Yes, that works but only 120dB down at 4KHz.
>>>>>>>>>>>>>>>>>>> I put the damping resistor back to 47k since I don't care what happens during the first few seonds as long as it
>>>>>>>>>>>>>>>>>>> happens.
>>>>>>>>>>>>>>>>>>> If it's necessary to wait one minute for the purest tone, that's fine with me.
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>> Linewraps are going to be a problem - delete all "\n" from the last few lines
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>> You don't want to remove \n just remove the wraps.
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>> BCM61B does not have two independent transistors.
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>> So you probably want BCM847BS which has two independent matched transistors and a very low price at digikey, so
>>>>>>>>>>>>>>>>>>> may
>>>>>>>>>>>>>>>>>>> as
>>>>>>>>>>>>>>>>>>> well
>>>>>>>>>>>>>>>>>>> use
>>>>>>>>>>>>>>>>>>> two
>>>>>>>>>>>>>>>>>>> of them as shown below.
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>> I took the model from
>>>>>>>>>>>>>>>>>>> https://github.com/peteut/spice-models/blob/master/nxp/complex_discretes/complex_discretes.txt
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>> It should only be necessary to unwrap the last line of the following.
>>>>>>>>>>>>>>>>>>> Don't remove \n just remove the wraps, you may need to use a horizontal scroll bar.
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>> Version 4.1
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>> Best to just offset the integrator output so the amplitude is brought
>>>>>>>>>>>>>>>>>> under control sooner.
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>> Wow. That has much lower distortion too.
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> If you just replace Q1,2 duals with a simple long tailed pair I think
>>>>>>>>>>>>>>>> you will get better performance.
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> I'm not sure I understand how the multiplier could be implemented with just a long tailed pair.
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> Just modulate the tail current and select how much to steer to the
>>>>>>>>>>>>>> output by directly driving the bases rather than indirectly as in your
>>>>>>>>>>>>>> circuit.  The following link shows one example topology, and a four
>>>>>>>>>>>>>> quadrant differential I/O version.  Compare the linearity of each of
>>>>>>>>>>>>>> them.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> https://1drv.ms/u/c/1af24d72a509cd48/EWVCUG7-jFJMu7-01VczCRcBzEC9JPHrV45x7TOunN90Gg?e=GXbvX5
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> It could be used as shown here.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> https://1drv.ms/u/c/1af24d72a509cd48/EVmMVrvUD15GutoR5nCJ7QEBSeZsHWpHudqR0b8XtTLMLw?e=HIV74I
>>>>>>>>>>>>>
>>>>>>>>>>>>> As I've already said, I like it. I've played with it a bit.
>>>>>>>>>>>>>
>>>>>>>>>>>>> The ON-Semiconductor NSS40301MDR2G NPN dual comes with a 2mV guaranteed maximum difference in base-emitter voltages (at
>>>>>>>>>>>>> the
>>>>>>>>>>>>> same
>>>>>>>>>>>>> emitter current). Edward Rawde's Nexperia BCM61B dual part has matched current gain, but no guarantee on the Vbe. The
>>>>>>>>>>>>> Nexperia
>>>>>>>>>>>>> BCM847BS does offer 2mV base-emitter matching, and would presumably work just as well.
>>>>>>>>>>>>>
>>>>>>>>>>>>> Putting in the ON-Semiconductor dual means that your gain control circuit doesn't have to waste output swing coping with
>>>>>>>>>>>>> part-to-part variation.
>>>>>>>>>>>>>
>>>>>>>>>>>>> I've added a cascode transistor (Q1, it should be Q4) to minimise any Early effect distortion.
>>>>>>>>>>>>>
>>>>>>>>>>>>> I've snipped out the op amp driving the base of Q3. Once you'd gone AC-coupled, it wasn't doing anything useful.
>>>>>>>>>>>>>
>>>>>>>>>>>>> And I've put a string of eight diodes in series with R10. They nominally compensate for the temperature dependence
>>>>>>>>>>>>> introduced
>>>>>>>>>>>>> by
>>>>>>>>>>>>> the four rectifier diodes D2, D12, D13 and D14. In this version of the circuit the rectifiers knock about 0.6 volts off
>>>>>>>>>>>>> a
>>>>>>>>>>>>> sine
>>>>>>>>>>>>> wave that peaks at 3.8V, about a quarter of the 15V rail. I haven't run the numbers to fix the best number of diodes,
>>>>>>>>>>>>> but
>>>>>>>>>>>>> something between six and eight looks okay.
>>>>>>>>>>>>>
>>>>>>>>>>>>> The harmonics aren't great - most of them are about 90dB below the fundamental, but the seventh is only 85dB down.
>>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>> Not sure I see the point if it's only 80dB down Bill.
>>>>>>>>>>>> @ 7Khz in LTSPice 24.1.5
>>>>>>>>>>>
>>>>>>>>>>> LTSpice isn't all that reliable as predictor of low level distortion. Having an armoury of different circuits to try when
>>>>>>>>>>> you
>>>>>>>>>>> finally get around to building  and testing something real may be useful.
>>>>>>>>>>>
>>>>>>>>>>>> I can almost get that from a simple phase shift oscillator and a 1KHz tuned circuit.
>>>>>>>>>>>
>>>>>>>>>>> I'm sure that you think so. John Larkin thought that a bang-bang amplitude control was worth suggesting...
>>>>>>>>>>>
>>>>>>>>>>>> The last time I included a diode string like that in one of my circuits (which I seem to recall had better than 80dB
>>>>>>>>>>>> performance)
>>>>>>>>>>>> you told me it was nuts.
>>>>>>>>>>>
>>>>>>>>>>> It probably was. In this case there are better ways of getting a rectified output than a simple series diode - I've posted
>>>>>>>>>>> circuits which incorporate precision rectifiers which get rid of the forward drop through the diode, and I've built
>>>>>>>>>>> circuits
>>>>>>>>>>> that
>>>>>>>>>>> used synchronous rectifiers built around transmission gates where the output isn't shifted by a temperature dependent
>>>>>>>>>>> diode
>>>>>>>>>>> drop.
>>>>>>>>>>> It went into a GaAs single crystal puller as a retrofit.
>>>>>>>>>>>
>>>>>>>>>>> The main point of the diode string was as a satirical comment on that aspect of the design you posted, which probably
>>>>>>>>>>> counts
>>>>>>>>>>> as
>>>>>>>>>>> being hostile, but I am hostile to ill-thought out designs, hard though it is to get the design time to sort them out.
>>>>>>>>>>
>>>>>>>>>> I don't see anything particularly hostile there Bill. Just different points of view.
>>>>>>>>>>
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