On Wed, 14 May 2014 11:43:03 -0700 (PDT), haiticare2011@gmail.com wrote:>On Wednesday, May 14, 2014 10:46:54 AM UTC-4, Joerg wrote: >> haitdicare2011@gmail.com wrote: >> >> > On Tuesday, May 13, 2014 9:30:08 PM UTC-4, Phil Allison wrote: >> >> >> "skeptical engineer" >> >> >> >> >> >> >> >> >> >> >> >>> I was looking at the SAW oscillator circuits at a co. called >> >> >>> Epcos, and they just take an op amp with the SAW filter in the feedback >> >> >>> loop. They explain that the op amp amplifies noise, but preferentially >> >> >>> at the filter allowed frequency. 2 components. >> >> >> >> >> >> >> >> >> ** I see no "op-amps " in their VHF /UHF oscillator designs. >> >> >> >> >> >> >> >> >> >> >> >> You need to post a link to stuff like that. >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> .... Phil >> >> > >> >> > OK - right you are. >> >> > http://www.mouser.com/pdfdocs/_Application%20Toolkit_050518_17h.pdf >> >> > See page 10. >> >> > >> >> > This is posted at Mouser, but it is an Epcos doc. The question is, would an >> >> > op-amp (generic amplifier) work in this circuit? >> >> > >> >> >> >> That's not an opamp but a generic amplifier, and only meant as >> >> illustration, as an amp "building block". Yes, a fast enough opamp can >> >> do this but that isn't necessarily the wisest and most frugal approach. >> >> Cheapskates use logic parts for that because you get a six-pack for a >> >> nickel :-) >> >> >> >> -- >> >> Regards, Joerg >> >> >> >> http://www.analogconsultants.com/ > >OK thanks. - What logic part would produce a sine wave output?A 'U' inverter? Something like a 74HCU04?
Heck of a way to run an oscillator?
Started by ●May 13, 2014
Reply by ●May 14, 20142014-05-14
Reply by ●May 15, 20142014-05-15
On Tue, 13 May 2014 06:14:54 -0700 (PDT), skeptical engineer <haiticare2011@gmail.com> wrote:>I was looking at the SAW oscillator circuits at a co. called >Epcos, and they just take an op amp with the SAW filter in the feedback >loop. They explain that the op amp amplifies noise, but preferentially >at the filter allowed frequency. 2 components. > >I love the simplicity, but does this approach have any drawbacks?According to Barkhausen, you just need an active element with sufficient gain and a frequency selective component in the (positive) feedback path. When first switched on, the amplifier input related thermal noise is amplified, Part of it is going to the frequency sensitive network, which attenuates the lowest and highest frequencies, leaving a broad peak around the resonant frequency. This quite broad peak goes into the amplifier input, being amplitude to a larger amplitude than the thermal noise. After a few iterations, the lower and higher noise sidebands are attenuated and the peak amplitude at resonance is increasing, finally creating a narrow spectral line. To sustain oscillation, the amplifier gain must be greater than the losses in the feedback loop and the phase shift must be such that there is a positive feedback. Of course, the amplitude can't grow forever, but is limited by the amplifier output voltage swing. Alternatively, the amplifier gain needs to be reduced to keep the voltage within the amplifier output swing in order to generate a clean sine wave, such as in the Wien bridge oscillator. Even if this Barkhausen explanation assumes a linear amplifier so that the thermal noise gets amplified in the first place, in practice, a class C amplifier might be usable, since the switch on transient will contain frequency components that will be amplified and looped back. While such circuit would start reliably with a battery power supply and a power-on switch, the same circuit might not start, when plugging a power supply into a mains socket, due to the slow DC voltage build up and thus no high frequency components.
Reply by ●May 15, 20142014-05-15
<haiticare2011@gmail.com>> Phil Allison wrote: >> "skeptical engineer" >> >> >I was looking at the SAW oscillator circuits at a co. called >> >> > Epcos, and they just take an op amp with the SAW filter in the feedback >> >> > loop. They explain that the op amp amplifies noise, but preferentially >> >> > at the filter allowed frequency. 2 components. >> >> ** I see no "op-amps " in their VHF /UHF oscillator designs. >> >> You need to post a link to stuff like that.> > OK - right you are. > http://www.mouser.com/pdfdocs/_Application%20Toolkit_050518_17h.pdf > See page 10.** No op-amps in sight. There are app notes on the Epcos sight that show a one ( UHF) transistor stage with many parts.> This is posted at Mouser, but it is an Epcos doc. The question is, would > an > op-amp (generic amplifier) work in this circuit?** Not at 400+ MHz - pal. You ARE dreaming. ... Phil
Reply by ●May 15, 20142014-05-15
meow2222@care2.com wrote:> On Tuesday, May 13, 2014 2:14:54 PM UTC+1, skeptical engineer wrote: > >> I was looking at the SAW oscillator circuits at a co. called >> Epcos, and they just take an op amp with the SAW filter in the feedback >> loop. They explain that the op amp amplifies noise, but preferentially >> at the filter allowed frequency. 2 components. >> I love the simplicity, but does this approach have any drawbacks? > > The amp just needs to be in its linear region to begin with > > > NTPhase gain is a deciding factor..
Reply by ●May 15, 20142014-05-15
On Thu, 15 May 2014 09:29:42 +1000, Clifford Heath <no.spam@please.net> wrote:>On 15/05/14 04:43, haiticare2011@gmail.com wrote: >> On Wednesday, May 14, 2014 10:46:54 AM UTC-4, Joerg wrote: >>> Cheapskates use logic parts for that because you get a six-pack for a >> OK thanks. - What logic part would produce a sine wave output? > >One that has no extra gain than what is required to start, so it's not >constantly slamming against the amplitude limit. One that limits its >amplitude into a resistive load. Or one fitted with an AGC circuit. It >helps if the clipping is somewhat soft. Look at the 74HCU04 inverters >for a start."Clipping" is for digital guys. AGC is necessary for low distortion. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
Reply by ●May 15, 20142014-05-15
Jim Thompson wrote:> On Thu, 15 May 2014 09:29:42 +1000, Clifford Heath > <no.spam@please.net> wrote: > >> On 15/05/14 04:43, haiticare2011@gmail.com wrote: >>> On Wednesday, May 14, 2014 10:46:54 AM UTC-4, Joerg wrote: >>>> Cheapskates use logic parts for that because you get a six-pack for a >>> OK thanks. - What logic part would produce a sine wave output? >> One that has no extra gain than what is required to start, so it's not >> constantly slamming against the amplitude limit. One that limits its >> amplitude into a resistive load. Or one fitted with an AGC circuit. It >> helps if the clipping is somewhat soft. Look at the 74HCU04 inverters >> for a start. > > "Clipping" is for digital guys. AGC is necessary for low distortion. >Yes, AGC is how it's done. Or follow it with a resonant circuit or LC lowpass filter. -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●May 15, 20142014-05-15
On Thu, 15 May 2014 11:22:55 -0700, Joerg <invalid@invalid.invalid> wrote:>Jim Thompson wrote: >> On Thu, 15 May 2014 09:29:42 +1000, Clifford Heath >> <no.spam@please.net> wrote: >> >>> On 15/05/14 04:43, haiticare2011@gmail.com wrote: >>>> On Wednesday, May 14, 2014 10:46:54 AM UTC-4, Joerg wrote: >>>>> Cheapskates use logic parts for that because you get a six-pack for a >>>> OK thanks. - What logic part would produce a sine wave output? >>> One that has no extra gain than what is required to start, so it's not >>> constantly slamming against the amplitude limit. One that limits its >>> amplitude into a resistive load. Or one fitted with an AGC circuit. It >>> helps if the clipping is somewhat soft. Look at the 74HCU04 inverters >>> for a start. >> >> "Clipping" is for digital guys. AGC is necessary for low distortion. >> > >Yes, AGC is how it's done. Or follow it with a resonant circuit or LC >lowpass filter.Filters, unless they're dead-on, introduce phase shift. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
Reply by ●May 15, 20142014-05-15
Jim Thompson wrote:> On Thu, 15 May 2014 11:22:55 -0700, Joerg <invalid@invalid.invalid> > wrote: > >> Jim Thompson wrote: >>> On Thu, 15 May 2014 09:29:42 +1000, Clifford Heath >>> <no.spam@please.net> wrote: >>> >>>> On 15/05/14 04:43, haiticare2011@gmail.com wrote: >>>>> On Wednesday, May 14, 2014 10:46:54 AM UTC-4, Joerg wrote: >>>>>> Cheapskates use logic parts for that because you get a six-pack for a >>>>> OK thanks. - What logic part would produce a sine wave output? >>>> One that has no extra gain than what is required to start, so it's not >>>> constantly slamming against the amplitude limit. One that limits its >>>> amplitude into a resistive load. Or one fitted with an AGC circuit. It >>>> helps if the clipping is somewhat soft. Look at the 74HCU04 inverters >>>> for a start. >>> "Clipping" is for digital guys. AGC is necessary for low distortion. >>> >> Yes, AGC is how it's done. Or follow it with a resonant circuit or LC >> lowpass filter. > > Filters, unless they're dead-on, introduce phase shift. >For most oscillators that act as master or are in similar functions it does not matter. -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●May 15, 20142014-05-15
<upsidedown@downunder.com> wrote in message news:vqh8n9p23ldhc76l7m1fd1fbpq0qrekdnn@4ax.com...> Even if this Barkhausen explanation assumes a linear amplifier so that > the thermal noise gets amplified in the first place, in practice, a > class C amplifier might be usable, since the switch on transient will > contain frequency components that will be amplified and looped back. > > While such circuit would start reliably with a battery power supply > and a power-on switch, the same circuit might not start, when plugging > a power supply into a mains socket, due to the slow DC voltage build > up and thus no high frequency components.Also, easy to lock up if the oscillation gets quenched. Self-excited class C oscillators are rarely class C under all conditions, but nonetheless are often succeptible to quenching, which is irritating from time to time... Tim -- Seven Transistor Labs Electrical Engineering Consultation Website: http://seventransistorlabs.com
Reply by ●May 16, 20142014-05-16
"Jim Thompson" wrote in message news:vbj9n9p3gebit51f22nagtmlfo3uaebe7p@4ax.com... On Thu, 15 May 2014 09:29:42 +1000, Clifford Heath <no.spam@please.net> wrote:>>On 15/05/14 04:43, haiticare2011@gmail.com wrote: >>> On Wednesday, May 14, 2014 10:46:54 AM UTC-4, Joerg wrote: >>>> Cheapskates use logic parts for that because you get a six-pack for a >>> OK thanks. - What logic part would produce a sine wave output? > >>One that has no extra gain than what is required to start, so it's not >>constantly slamming against the amplitude limit. One that limits its >>amplitude into a resistive load. Or one fitted with an AGC circuit. It >>helps if the clipping is somewhat soft. Look at the 74HCU04 inverters >>for a start.>"Clipping" is for digital guys. AGC is necessary for low distortion.Usually, however, clipping/clamping/limiting pretty much invariably produces the lowest phase noise. Simple principle, is the more devices, the more noise. I have actually spent some time running sims on just about every reasonable oscillator topology you can imagine for phase noise. One transistor wins. Kevin Aylward B.Sc. www.kevinaylward.co.uk www.anasoft.co.uk - SuperSpice
