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Path: ...!eternal-september.org!feeder3.eternal-september.org!usenet.blueworldhosting.com!diablo1.usenet.blueworldhosting.com!nnrp.usenet.blueworldhosting.com!.POSTED!not-for-mail From: "Edward Rawde" <invalid@invalid.invalid> Newsgroups: sci.electronics.design Subject: Re: Low distortion sinewave oscillator without big capacitor. Date: Tue, 8 Apr 2025 11:56:57 -0400 Organization: BWH Usenet Archive (https://usenet.blueworldhosting.com) Lines: 301 Message-ID: <vt3h0a$deg$1@nnrp.usenet.blueworldhosting.com> References: <vsc420$2ic$1@nnrp.usenet.blueworldhosting.com> <qq8tujlpciqc2jrd0ibljmjr9pd37ip6hi@4ax.com> <vsn5df$o10$1@nnrp.usenet.blueworldhosting.com> <vh9uujhi6chpejn8nfhdh67afc23kfqq32@4ax.com> <vsnufh$2ou7j$1@dont-email.me> <vsp86r$174f$1@nnrp.usenet.blueworldhosting.com> <add0vjdh2gcma0n9pfunq76n04cfbkhtnj@4ax.com> <vspff8$a02$1@nnrp.usenet.blueworldhosting.com> <uop0vjp3d13t441ujfboi5aeeg08anm1je@4ax.com> <vsq9j1$pcn$1@nnrp.usenet.blueworldhosting.com> <tcl2vjp49q4ga21itrpnmr4u3ts06vqffd@4ax.com> <vsu092$14oc7$1@dont-email.me> <vsu3mr$2h3c$1@nnrp.usenet.blueworldhosting.com> <vsuacb$1d4ec$1@dont-email.me> <vsudei$2mhi$1@nnrp.usenet.blueworldhosting.com> <vsvspr$33gdd$1@dont-email.me> <vt0it4$18dh$1@nnrp.usenet.blueworldhosting.com> <vt2bck$1gmbm$1@dont-email.me> Injection-Date: Tue, 8 Apr 2025 15:56:59 -0000 (UTC) Injection-Info: nnrp.usenet.blueworldhosting.com; logging-data="13776"; mail-complaints-to="usenet@blueworldhosting.com" Cancel-Lock: sha1:0b3gUOp/d3oluP4cWE+dTiaL8Pc= sha256:pjKMMFhszb7a7fUENAE7hiScYax2qcWlp82CGl3HPz8= sha1:UJodDmWKpBsV7405xHvaCbN+2lg= sha256:Cy4kebXcS+OoMQxNEI/jrGtKz6NligpABhEYlTxctfI= X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.6157 X-Newsreader: Microsoft Outlook Express 6.00.2900.5931 X-RFC2646: Format=Flowed; Response X-Priority: 3 X-MSMail-Priority: Normal Bytes: 17275 "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. >>>> >>>>> I've got stuck with sorting out other peoples half-baked designs often enough, but only after my bosses had had their noses >>>>> rubbed >>>>> in the unfortunate consequences. >>>> >>>> When I started work as a fresh graduate (but one who also had practical experience with everything from TV antenna systems in >>>> hospitals to AY-3-8500 based games) I was amazed at some of the analogue circuit design blunders I encountered. >>>> In one case I built a piece of custom test equipment which needed +15V and -15V. An available transformer had two suitable >>>> isolated >>>> secondary windings so I just used two 7815 devices. >>>> Only to be told by a more experienced "Designer" that connecting the output of a 7815 to ground would short it out and I had to >>>> use >>>> 7915 for that..... >>> >>> What he should have said was the you were messing up the ground returns by hooking up the +15V output of the second 7815 to the >>> 0V >>> rail. >>> >>> He was avoiding spending a long time talking about grounding and shielding, which is a rather specialised subject. >> >> I see. Thank you for letting me know what he was thinking Bill. >> Do you have some kind of time machine that you travel around in so you can have a better knowledge of what happened in a past >> situation when compared with someone who was actually there at the time? >> >>> >>> In this particular thread your eight transistor is bonkers, but it >>> works - not that I can see how. >> >> Seems pretty obvious to me how it works Bill. > > But John May could take out half the transistors and produce a circuit that still worked. One reason for that is that a current source/sink can be approximated by a high value resistor so instead of using a current mirror ========== REMAINDER OF ARTICLE TRUNCATED ==========