The LTC1540 would be spending most of its time "doing nothing". Most of its time it will spend near a rail.
The input current doesn't rise much when the difference voltage goes up so the resistors can be many meg.
Post it yourself, if you are so keen to see it. The OP hasn't asked for it, and I'm not motivated to do you any favours.
If you wanted to prove how clever you are. you could try to post a circuit for a 50% duty cycle emitter-coupled astable multvibrator - the smaller voltage swing at the active devices would reduce the current consumption over the more familiar collector-coupled design, and would make it easier to preserve a thin base-emtter junction, if you could get it to work.
-- Bill Sloman, Nijmegen
-- Is English not your first language? Here\'s the OP\'s post, ya goddam liar: "I\'m looking for a schematic for a square wave oscillator which draws around 10uA, powered by 2 to 5V and oscillates at around 100kHz with a 50% duty cycle. I tried out some schematics around a 4007 but none can meet all the requirements. any suggestions here? regards, nukeymusic"
Scale the impedances up from this...
For non-precision work I'd delete R4 and R5 rather than scaling them up. Then connect right end of C1 directly to U2A:pin2
...Jim Thompson
-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at
Pity about the square wave requirement - that's where a lot of the power goes, and a sinusoidal output can have fair dv/dt through the logic transition levels.
The usual complications and expense show up in anything with inductive energy storage..........
RL
That drives U1A's input diodes...naughty naughty!
Any idea what the average crossover current on that gadget is? The spikes are mA; the average could be a bunch. A 74hcu04 might help, or one of those CMOS transistor arrays things, CD4007 (?).
Here's a low-tech method:
Vcc +2v (regulated) / 8uA -+- | +--------------+--------------------+ | | R4 | R1 | | 100K 100K Q1 | R3 | | 2n3904 |/ .--470K--+-------+------> 102KHz +------+-----| C1 | | | 250mV p-p R2 | | |>. 100nF | |/ | (semi-sinewave) 680K | | .--||--+------| | | | | | Q2 |>. | === | | === 2n3904 | | GND | | GND | | | '--------------------+ | | R5 | | | 220K | | | | | === | | Ct GND | | 20pF | '----------------||------------------'
I didn't use all the current, leaving some for a buffer.
With regular transistors you have to keep everyone from saturating otherwise they're way too slow. RF transistors would be easier--you could probably just spin a bog-standard multivibrator and get better symmetry to boot.
Yours is simpler and cuter, if the current's okay.
Best regards, James Arthur
[snip]
On-chip, which is where I do that, there are NO ESD diodes ;-)
And I use single stage inverters ala 'HCU04 except much smaller.
...Jim Thompson
-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | | | | Vote Barack... Help Make America an Obama-nation | | | | Due to excessive spam, googlegroups, UAR & AIOE are blocked! |
I can't see the OP's post because he uses Google. He could check whether he can make an oscillator out of one of these since they've got a nice hysteresis:
Get the lowest voltage part available to minimize capacitive voltage swing.
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
First, low voltage. A fresh silver cell is just 1.55V. Then the clock never really feeds anything except the input of a divider chain within the chip. They'll probably do their darndest to keep its capacitance to a minimum.
A square wave oscillator won't be a nice resonant architecture. So you'll have to muscle capacitive charges around and it will consume more power. It's like wanting to rapidly move the pendulum of a grandfather's clock between its end points. This is why the OP might want to think about whether it really has to be a square wave.
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
It does seem clear that's important.
That was helpful. Do you imagine that they may use an LC, though, and attemp to retain as much energy there as possible? Or, as you seem to suggest to me, graduate the transfer of charge more trapezoidally and not use magnetic field storage, at all?
I kind of imagine that the usual crystal model most of us are likely to use has also been tremendously refined by watchmakers into a very, very proprietary one -- one that models the physics much better -- and that they use that in combination with thoughtful design. But I have to say that everytime I think about trying to do a 32kHz oscillator at very low power using discrete parts I just learn to appreciate how much good work has gone into what is now a very cheap watch.
Jon
:
He's had enough feedback to let him get on and do something for himself if he's anything like competent - and this is sci.electroncs.design, not sci.electronics.basics. If he really wants a schematic he could e-mail me directly (the e-mail address I post here is real and has been since before people strarted harvesting them) or he could ask here. Without that much feedback, I'm not going to bother.
You failed your chance to prove your own competence. An emitter- coupled monstable can't be made to produce a 50% duty cycle, and if you operated at my level, you'd know - or be able to work it out.
So you'd like to think. Dream on.
-- Bill Sloman, Nijmegen
[snip]
As usual Slowman is so full of shit his eyes are brown, see my 50% duty cycle device from the mid-60's...
...Jim Thompson
-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | | | | Vote Barack... Help Make America an Obama-nation | | | | Due to excessive spam, googlegroups, UAR & AIOE are blocked! |
Well, a 74HC14 will work at that power input and it oscillates fine with a single resistor and capacitor (remember to ground the five unused inputs).
Alas, the quiescent current with that one input floating around the threshold is not as low as one would like. An old RCA application note, ICAN-6230, seems to indicate that 100 kHz operation will be well over a milliwatt (at
5V, that means 200 uA). That note was on the old 4000 series CMOS, though, so you might find the 'HC series can outperform that analysis.Others have suggested discrete transistor oscillators; that's your best bet. An LC or mechanical resonator (OK, quartz crystal or ceramic nowadays, but I still recall tuning forks with coils of wire...) can be less lossy than an RC timer.
For once Jim has got a detail right - my eyes are brown - but (as usual) the rest of the message is severely out of touch with reality. Given as many transistors to play with as Jim used in the MC1658 even I could probably make a sort of emitter-coupled multivibrator with a
50% duty cycle (though it would certainly involve a lot of false starts). The classic two-transistor emitter-coupled multivibrator is rather less flexible. The OP application would probably require a third transistor to get enough voltage swing at the output.-- Bill Sloman, Nijmegen
They also current limit the drive to the crystal. PIC datasheets have a warning in the small print to use a series resistor when using watch crystals in low power mode to avoid overdriving them. I have seen the odd PIC manage 12uA running on a 3v supply with a 32768Hz xtal (ISTR the CPUs square wave clock is then 8192Hz) which isn't too far off the spec.
100kHz would obviously be a bit more thirsty for juice.Loose use of words? I assumed he wanted a good squarewave buffered output, but probably does not care about the internals.
The crystal is gently driven and the sine waveform amplified by a buffer to generate the square wave clock. An xtal has very high Q so it doesn't need much encouragement apart from initially to start up.
I suspect it would be OK using a watch xtal 32kHz or 100kHz. Although I have never tried to do it with discrete parts.
Regards, Martin Brown
** Posted from
Sure, that's why I suggested to try a very low power VCC monitoring chip as oscillator. Whether it'll get low enough in Ic I don't kniow, haven't tried yet.
Yes, but one has to watch out for capacitances in the last stage, the one to square up the waveform. Every pF counts.
He might need a custom made 100kHz crystal or try something on the 3rd of a watch crystal but that won't be exactly 100kHz.
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
-- He already did ask here, so why don\'t you just post what you\'ve got? LOL, as if you had anything to post except excuses...
-- :-) JF
Jim Thompson a écrit :
Delete R4/R5 and replace the cap with a two identical caps divider. (and you're saving one component)
-- Thanks, Fred.
te:
:rote:
ote:
As if I had anything to post that you could understand - you may be able to pose as a guru on sci.electronics.basis, but around here you are a rube.
If you had mastered more than minimal literacy, you'd realise that I never claimed that an emitter-coupled monstable could be persuaded to produce a 50% duty cycle - I merely invited you to attempt the impossible (in the context of a two-transistor circuit, which Jim's MC1658 isn't). A slightly more perceptive reader would have got the message from way I worded the invitation, even if they were as ignorant about multivibrators as you have proved to be.
This isn't the first time you've failed to read what I've actually written and I was fairly sure that I could give you enough rope to hang yourself.
You do make these claims. Who do you think is going to believe them?
You've made a fool of yourself and are now retreating behind the usual screen of scatalogical abuse.
-- Bill Sloman, Nijmegen
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.