LT Spice schmitt oscillator
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From: amdx on 9 Oct 2009 07:52 "Rich Grise" <richgrise(a)example.net> wrote in message news:pan.2009.10.08.22.52.29.197291(a)example.net... > On Thu, 08 Oct 2009 14:46:34 -0700, John Larkin wrote: > >> Does anybody have a working LT Spice netlist for a simple schmitt >> inverter/R-C oscillator? I tried one using the library schmitt inverter >> and get obscure sim errors, and I don't understand the HELP stuff. >> >> What's the third pin in the corner for? Ground? >> > We don't do homework. ;-P > > Cheers! > Rich > uuuhhh! Mike:-)
From: MooseFET on 9 Oct 2009 09:12 On Oct 8, 2:46 pm, John Larkin <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > Does anybody have a working LT Spice netlist for a simple schmitt > inverter/R-C oscillator? I tried one using the library schmitt > inverter and get obscure sim errors, and I don't understand the HELP > stuff. > > What's the third pin in the corner for? Ground? When you want to run a logic gate between 24V and 29V, it is nice to have a ground reference pin. > > Thanks, > > John Others have already helped you out on your actual question. The logic gate things are all infinitely fast or faster unless you put in the optional parameters for speed. The classic toggling flip flop doesn't work right unless you slow down the flipflop etc. LTSpice doesn't do well when a string of devices have gain and no delay. Those nice folks at Linear did me a big favor when they put the logic gates in. I have used them to model fairly complex logic in with the analog circuits.
From: John Larkin on 9 Oct 2009 14:45 On Thu, 08 Oct 2009 15:52:29 -0700, Rich Grise <richgrise(a)example.net> wrote: >On Thu, 08 Oct 2009 14:46:34 -0700, John Larkin wrote: > >> Does anybody have a working LT Spice netlist for a simple schmitt >> inverter/R-C oscillator? I tried one using the library schmitt inverter >> and get obscure sim errors, and I don't understand the HELP stuff. >> >> What's the third pin in the corner for? Ground? >> >We don't do homework. ;-P > >Cheers! >Rich I want to make a low-frequency triangle wave, 1 KHz maybe, to FM spread-spectrum a bunch (namely 5) of switching regulators on this board I'm doing, so that they don't leak into the ADC and show up in the eventual FFTs we're going to do and make birdies in the spectra. Neither the amplitude nor the frequency is very critical. An NC7S14M5 running at 3.3 volts will give me about a 0.9 volt p-p triangle. John
From: Joerg on 9 Oct 2009 15:05 John Larkin wrote: > On Thu, 08 Oct 2009 15:52:29 -0700, Rich Grise <richgrise(a)example.net> > wrote: > >> On Thu, 08 Oct 2009 14:46:34 -0700, John Larkin wrote: >> >>> Does anybody have a working LT Spice netlist for a simple schmitt >>> inverter/R-C oscillator? I tried one using the library schmitt inverter >>> and get obscure sim errors, and I don't understand the HELP stuff. >>> >>> What's the third pin in the corner for? Ground? >>> >> We don't do homework. ;-P >> >> Cheers! >> Rich > > I want to make a low-frequency triangle wave, 1 KHz maybe, to FM > spread-spectrum a bunch (namely 5) of switching regulators on this > board I'm doing, so that they don't leak into the ADC and show up in > the eventual FFTs we're going to do and make birdies in the spectra. > > Neither the amplitude nor the frequency is very critical. An NC7S14M5 > running at 3.3 volts will give me about a 0.9 volt p-p triangle. > Why so expensive? To spread things nicely you'll probably want five individual oscillators all running at different and non-correlating frequencies. Why not just use one 74HC14 for all of them and then use Schmitt inverter #6 for a blinkenlight or something? -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: John Larkin on 10 Oct 2009 01:09
On Fri, 09 Oct 2009 12:05:31 -0700, Joerg <invalid(a)invalid.invalid> wrote: >John Larkin wrote: >> On Thu, 08 Oct 2009 15:52:29 -0700, Rich Grise <richgrise(a)example.net> >> wrote: >> >>> On Thu, 08 Oct 2009 14:46:34 -0700, John Larkin wrote: >>> >>>> Does anybody have a working LT Spice netlist for a simple schmitt >>>> inverter/R-C oscillator? I tried one using the library schmitt inverter >>>> and get obscure sim errors, and I don't understand the HELP stuff. >>>> >>>> What's the third pin in the corner for? Ground? >>>> >>> We don't do homework. ;-P >>> >>> Cheers! >>> Rich >> >> I want to make a low-frequency triangle wave, 1 KHz maybe, to FM >> spread-spectrum a bunch (namely 5) of switching regulators on this >> board I'm doing, so that they don't leak into the ADC and show up in >> the eventual FFTs we're going to do and make birdies in the spectra. >> >> Neither the amplitude nor the frequency is very critical. An NC7S14M5 >> running at 3.3 volts will give me about a 0.9 volt p-p triangle. >> > >Why so expensive? To spread things nicely you'll probably want five >individual oscillators all running at different and non-correlating >frequencies. Why not just use one 74HC14 for all of them and then use >Schmitt inverter #6 for a blinkenlight or something? 3.7 cents is expensive? I thought about splattering them separately, but don't really see any advantage. Each switcher has one resistor to set its nominal frequency and one more to set the FM amount. They should be all over the place. John |