Analog Memory - Page 1
Forum section: electronics / projects

author: IntegratedValve
author_rank: Regular Contributor
timestamp: January 20, 2014, 05:14:38 pm
content: Is there any analog component/device/circuit capable of storing analog signal for a specified interval without using any digital stuff?

author: hlavac
author_rank: Frequent Contributor
timestamp: January 20, 2014, 05:30:57 pm
content: Do you mean a) single analog level or b) waveform?a) A capacitor?b) Pool of mercury with piezo elements at the ends?Crystal delay line from analog TV?Few dozen meters of coax cable transmission line?

author: richard.cs
author_rank: Super Contributor
timestamp: January 20, 2014, 05:35:17 pm
content: Further options for b):iii) Loop of magnetic tapeiv) Bucket-brigade chip (http://www.electrosmash.com/mn3007-bucket-brigade-devices)v) A few miles of coax on a drumvi) Modulated RF bounced off the moon

author: IntegratedValve
author_rank: Regular Contributor
timestamp: January 20, 2014, 05:38:23 pm
content: I need something like a 2 port device, when connecting one port to input signal, it stores the exact waveform shape, not necessarily the same magnitude, for a specific interval. When input signal disconnected, the stored signal remains until the output port is connected to a load, the signal is discharged.

author: c4757p
author_rank: Super Contributor
timestamp: January 20, 2014, 05:43:06 pm
content: An interesting problem with probably no practical solution. You could use a very large number of staggered sample-and-hold circuits. I suspect you could also make analog memory of that sort with a specialized cross between a storage CRT and a video camera tube. But ADC->RAM->DAC is probably your best bet...Perhaps you could find a SAD-1024 or SAD-512 bucket brigade delay chip. I don't know what their storage lifetime is, though.There are, of course, delay lines, but unless you only want to deal with very short waveforms, you will need a stupendously long line, and you still have to handle cycling the signal around the line until you need it, synchronizing pickup when you do need it, degradation of signal integrity and amplitude as it cycles...And by "stupendously long", I mean about 200 000 kilometers per second of delay, or just over half the distance to the moon.

author: zapta
author_rank: Super Contributor
timestamp: January 20, 2014, 05:49:16 pm
content: Anything wrong with digital?

author: IntegratedValve
author_rank: Regular Contributor
timestamp: January 20, 2014, 05:49:33 pm
content: With ADC/DAC I will lose precision and accuracy of wave shape, and I don't want to use any sort of digital or discrete clocking stuff, just pure analog.

author: c4757p
author_rank: Super Contributor
timestamp: January 20, 2014, 05:50:35 pm
content: Quote from: IntegratedValve on January 20, 2014, 05:49:33 pmUse agoodADC and DAC then. Any of these analog methods will degrade the signal even more than that!

author: hlavac
author_rank: Frequent Contributor
timestamp: January 20, 2014, 05:57:46 pm
content: Exactly. Use high enough resolution for the sampling noise to be insignificant to other noise already present, and you wont be able to see any difference.

author: Jon86
author_rank: Frequent Contributor
timestamp: January 20, 2014, 05:59:16 pm
content: 'The exact waveform shape?'Well in that case there's really no analog way to do it, at least not practically.If you were just storing an analog VOLTAGE you could've done that with a capacitor, but the only way to solve this is with a digital circuit. Depending on the accuracy/frequency you need to operate at, a microcontroller with an R2R DAC should work fine.

author: tszaboo
author_rank: Super Contributor
timestamp: January 20, 2014, 06:16:38 pm
content: Quote from: IntegratedValve on January 20, 2014, 05:14:38 pmYou can record it to vinyl. That is analog.

author: IntegratedValve
author_rank: Regular Contributor
timestamp: January 20, 2014, 06:46:00 pm
content: Quote from: NANDBlog on January 20, 2014, 06:16:38 pmWhat's vinyl? IC? I'm not going to use anything mechanical FYI.

author: IanB
author_rank: Super Contributor
timestamp: January 20, 2014, 06:56:12 pm
content: There is no way to do what you want in a purely analog way unless you can invent a time machine and work out a way to freeze time.This is because waves have time in their equations, which means they are moving, which means you can only store them in a dynamic buffer (such as a big long signal delay line as others have mentioned above). However, physics insists that any signal stored in a dynamic buffer will be degraded to some extent when it comes out the other end, so you have a limit on how accurately you can store the signal.The only way to store the signal with arbitrarily defined accuracy for an indefinite time is using digital techniques.

author: mamalala
author_rank: Unknown
timestamp: January 20, 2014, 06:56:33 pm
content: A BBD (Bucket Brigade Device) is basically what you look for:http://en.wikipedia.org/wiki/Bucket-brigade_deviceIt is basically a long chain of capacitors with switches between them, that transfers an analogue input signal to the output. It is (was?) often used in analogue audio effect units, etc. Dunno if they are still produced nowdays. Some old CCD elements used for scanners had an analogue input at the first element of the chain, somewhat allowing them to be used in the same way (altough i have only seen two of them, over a decade ago. After that i never saw such a CCD again). In any case, there willl always be some degradation of the signal when using a BBD.Otherwise i would also suggest the use of a ADC and DAC. You could do that in a rather minimal way by using ADC and DAC that provide a parallel data bus, with a dual-port SRAM inbetween them, and some address and r/w signal generation circuittry. That can be as simple as a bunch 74xx counter chips.Yet another rather common way is a spring reverb unit. Simply cut off the feedback between output and inputt to make it a simple delay. Although you get rather short delay times, and by nature these units are very sensitive to external mechanical influences, like vibrations, tapping, etc.Greetings,Chris

author: attie
author_rank: Contributor
timestamp: January 20, 2014, 06:57:15 pm
content: Quote from: IntegratedValve on January 20, 2014, 06:46:00 pmhttps://www.google.co.uk/search?q=vinyl&tbm=isch

author: branadic
author_rank: Super Contributor
timestamp: January 20, 2014, 07:10:31 pm
content: If not vinyl, what about audio tape?

author: Len
author_rank: Frequent Contributor
timestamp: January 20, 2014, 07:22:05 pm
content: Quote from: IntegratedValve on January 20, 2014, 06:46:00 pmI am officially an old man.

author: daqq
author_rank: Super Contributor
timestamp: January 20, 2014, 07:35:36 pm
content: There's this:http://en.wikipedia.org/wiki/Time_stretch_analog-to-digital_converterBut somehow I don't think it applies to your situation. There no single purely analog way of doing this. The simplest way is to sample the signal in discrete time with a digital solution. You should be able to use a single processor for that. Anything extra is just more complicated and at the end of the day doesn't give you a better solution.Single IC solutions are for instance here:https://www.nuvoton.com/NuvotonMOSS/Community/ProductInfo.aspx?tp_GUID=d2589477-840d-4046-9c3a-2e0e457048b3There are tape and other electromechanical solutions - like a delay line memory, but... well... yeah...

author: IntegratedValve
author_rank: Regular Contributor
timestamp: January 20, 2014, 07:43:02 pm
content: Thanks for suggestions. I think my best bet here is using high precision ADC/DAC.

author: Jon86
author_rank: Frequent Contributor
timestamp: January 20, 2014, 07:44:00 pm
content: Why are you so scared of digital?Unfortunately there's literally no practical way to do it with analog. Just give up and try digital.What's this for anyway? That might help quite a bit.

author: Chopsticks
author_rank: Regular Contributor
timestamp: January 21, 2014, 03:30:23 am
content: you can still buy BBD chips from [urlhttp://www.smallbearelec.comjust search for 'MN3' though with the cost per part it's probably not really worth it

author: casinada
author_rank: Frequent Contributor
timestamp: January 21, 2014, 04:27:32 am
content: This idea is as old as Edison

author: codeboy2k
author_rank: Super Contributor
timestamp: January 21, 2014, 09:35:32 am
content: Quote from: Jon86 on January 20, 2014, 07:44:00 pmYeah, I wish up front people would explain what they are doing, rather than tell us what they want and we go on for pages and pages.For example, someone might come on and start a thread saying they want a rope, and we go on pages and pages about all sorts of different ropes, and after 10 pages the OP finally divulges that its needed to hold a car to a trailer... so then a chain might have been better suggestion from the beginning.well you get my point.

author: TerraHertz
author_rank: Super Contributor
timestamp: January 21, 2014, 10:54:31 am
content: Quote from: IntegratedValve on January 20, 2014, 05:14:38 pmThat you don't provide a figure for this duration, and don't know what vinyl is, tells me you don't really have a clear idea of what you want, and are very young.That you're effectively asking for a time machine, but don't realize that, further brackets you.Anyway, if you only wanted about 64uS delay, you could use a piezo delay line as used for chroma processing in PAL TV receivers. If your signal could be modulated onto a suitable carrier.Other than that, it's mechanical or nothing. Magnetic tape, rotating drum or platter, etc. Oh hey, maybe the latest innovation, metal wire recorders. Or you could record the signal on a chart recorder, then play it back with some kind of optical sensor tracking the pen trace. I once found a temperature profile control system for a full sized brick firing kiln that used exactly that. So it does work. Just very slowly, as in a week or more to play back the chart.You didn't mention anything about bandwidth, so maybe that might work for you?

author: dannyf
author_rank: Super Contributor
timestamp: January 21, 2014, 04:12:08 pm
content: QuoteOther people have provided enough examples. A wire for example can be a (analog) memory device in that any signal showing up on one end of it takes time to reach the other end. If you have a sufficiently long wire and you pick a sufficiently slow transmission mechanism (sound vs. emf), you have a memory device that's fully analog. The delay-lines in old TVs are like that.

author: macboy
author_rank: Super Contributor
timestamp: January 21, 2014, 05:16:04 pm
content: Quote from: dannyf on January 21, 2014, 04:12:08 pmI don't think "a wire" can do this, but a transmission line can, that is, a piece of coaxial cable. This is commonly done in analog oscilloscopes to delay the signal to the vertical amplifiers so that the scope can trigger and start the sweep before (only nanoseconds before) the waveform hits the amp and shows on screen. This just barely allows the triggering portion of the waveform to be displayed on the screen. Inside such scopes, you will see a big coil of coaxial cable or sometimes a strange spiralled cable that is designed to give more delay per metre.So a big long piece of coax can provide a fixed delay at releatively high bandwidth. As already a mentioned, a BBD, also known as a CCD (Charge-coupled device) can provide a short term storage with arbitrary playback speed. They are discrete time (sampling) but do not quantize/decimate the signal (do reduce resolution to N bits). Does that count as digital? You tell me. My old Philips DSO uses CCD devices to sample at up to 250 MS/s, until the device is full, then the stored 'waveform' is played back to the actual ADC at about 100 kS/s to be digitised. For 1980's technology, 250 MS/s at 10 bits was pretty impressive. The limitations of a CCD/BBD is the storage size (usually a few hundred points at most) and the bandwidth limited by Nyquist.

author: IntegratedValve
author_rank: Regular Contributor
timestamp: January 21, 2014, 05:55:44 pm
content: Quote from: TerraHertz on January 21, 2014, 10:54:31 amSince you are moaning about it and want to know what I wanted that device for, I can tell:To see how you can think out of the box. ;-)

author: BravoV
author_rank: Super Contributor
timestamp: January 21, 2014, 06:02:13 pm
content: Quote from: Len on January 20, 2014, 07:22:05 pmMe too.But this is a fun thread to watch, subscribed.

author: dannyf
author_rank: Super Contributor
timestamp: January 21, 2014, 06:08:15 pm
content: QuoteIf you had a wire from the sun to the earth, it would have taken several seconds to send a signal to you.If you had a wire from here to Orion's belt, it would have taken several thousand years to send a signal to you.If you had a wire from here to the end of the universe, it would have taken 10+ billion years to send a signal to you.Yes, a wire can do this.

author: branadic
author_rank: Super Contributor
timestamp: January 21, 2014, 06:16:47 pm
content: QuoteNo, the signal would never reach the end of the universe because of the finite propagation speed of the signal inside the cable/wire and the accelerated expansion of the universe and on the other hand your cable length would have to increase with the expansion speed of the universeD'oh!

author: macboy
author_rank: Super Contributor
timestamp: January 21, 2014, 08:16:28 pm
content: Quote from: dannyf on January 21, 2014, 06:08:15 pmNo, a signal will not propagate along a single wire. It requires a transmission line with a fixed impedance, such as coax or twisted pair.

author: dannyf
author_rank: Super Contributor
timestamp: January 21, 2014, 08:19:29 pm
content: Quotesound on a steel rod?laser in a fibre?electrons in a copper wire?Of course, if you define "wire" different...

author: IanB
author_rank: Super Contributor
timestamp: January 21, 2014, 09:34:30 pm
content: Quote from: macboy on January 21, 2014, 08:16:28 pmYou do realize that if this statement were true then no electric or electronic circuits would ever work?

author: gregallenwarner
author_rank: Regular Contributor
timestamp: January 21, 2014, 09:39:49 pm
content: QuoteA signal will indeed propagate down a single wire at a particular speed, usually a significant fraction of the speed of light. To prove this, take a look at how many modern PC motherboards are designed:The designers didn't put all those wiggly traces in just for kicks. They did it in order to equalize the lengths of multiple parallel traces, so that all the signals reach the end at the same time. At speeds in the hundreds of megahertz, which is common in today's PC's, the propagation delay down these traces is a significant concern. Those traces can be thought of much like plain old wires; that is, they're not coax transmission lines, yet they still introduce a significant delay in the signal propagation.

author: branadic
author_rank: Super Contributor
timestamp: January 21, 2014, 09:47:43 pm
content: QuoteHave you ever heard about Microstrips?

author: gregallenwarner
author_rank: Regular Contributor
timestamp: January 21, 2014, 09:58:13 pm
content: Quote from: branadic on January 21, 2014, 09:47:43 pmA microstrip is not a co-ax configuration. The quote I referenced specifically mentioned two types of transmission lines: co-ax and twisted pair. Motherboard bus traces do not conform to either of those definitions.I suppose if you wanna get technical, then yes, motherboard traces are a form of transmission line, but then, so are free hanging wires floating in the air, because they will also have some coupled capacitance with respect to ground, albeit a very tiny amount. But the point of all this is to refute the claim that free-hanging wires do not suffer from propagation delays, which is false; they do.

author: tszaboo
author_rank: Super Contributor
timestamp: January 21, 2014, 11:27:57 pm
content: Quote from: IanB on January 21, 2014, 09:34:30 pmFrom that very little RF I actually understand, I think he is right.If you use a "wire" you have significant group delay on a transmission line. If you use a coax, matched impedances, and everything is ideal, than there is no group delay.Now, if there is group delay, the stuff you put in the cable is not necessarily comes out in the same order. Which means it is not FIFO, not a good memory.Can someone correct me please if I'm wrong?

author: TerraHertz
author_rank: Super Contributor
timestamp: January 22, 2014, 07:22:11 am
content: Quote from: macboy on January 21, 2014, 08:16:28 pmIncorrect. A single wire in free space _is_ a transmission line with a fixed impedance. The only reason we use coax and twisted pairs is to achieve a lower and controlled impedance, that does not vary depending on the proximity of random nearby objects. Also to reduce losses to free space.You can easily demonstrate that a single wire works as a transmission line, using a fast pulser and good scope.Edit to add: I think there is group delay in all kinds of transmission lines, induced by the characteristics of the materials involved. Skin effects in the wires, dielectric parameters of the medium around the wire(s), etc. Trying to minimize that is part of the art of transmission line design, no? I thought the only thing that doesn't exhibit group delay, is radio waves in a vacuum? (But it's not like I know what I'm talking about here.)

author: TerraHertz
author_rank: Super Contributor
timestamp: January 22, 2014, 07:41:41 am
content: Quote from: dannyf on January 21, 2014, 06:08:15 pmActually, I'm pretty sure if you laid a wire from the Sun to the Earth, several seconds later you'd have a humongous arc of many millions of amps, that would go on for quite a while. As the massive difference in potential charge between the Sun and Earth equalized.I'd recommend you _don't_ lay a wire between any two celestial bodies. Unless you want to play "Look Ma, I've entirely converted myself to ionized plasma."Starter reference: google nasa space tether electric universe

author: dannyf
author_rank: Super Contributor
timestamp: January 22, 2014, 04:06:14 pm
content: This discussion is evolving into a prime example of people who know so much that they know so little - they don't know what relevant knowledge to bring to a given discussion.