Analog circuits are fast: But how fast? - Page 1
Forum section: electronics / general

author: Beamin
author_rank: Super Contributor
timestamp: September 16, 2018, 02:07:01 pm
content: In a lot of posts and videos on the internet people always say "remember in analog circuits things work fast" Referring to how signals move around the circuit. But how fast? Or are they saying relative to clock speed in a micro the analog circuits work instantly (speed of light?)What can slow an analog circuit down? Putting in caps that would have to charge up each time something happens but somehow not block signal?

author: MK14
author_rank: Super Contributor
timestamp: September 16, 2018, 02:12:41 pm
content: Not as fast as Beamin can create new threads.Digital circuits are usually considered to be way faster.But analogue circuits, can do much more work, while it is settling on a new voltage, and anyway, you can have super fast analogue circuits (especially if you are allowed to include going to microwave frequencies, and even higher, probably), as well.But there are all sorts of drawbacks to analogue circuits, which digital circuits tend not to suffer from (drift, tolerance, susceptibility to interference, cost, needing trimmers, etc etc). They can be very tricky to design, and there are not that many people, who are really good at very fast analogue design.It can get very expensive as well.In many things, high speed digital systems, is the solution and winner.

author: Brumby
author_rank: Unknown
timestamp: September 16, 2018, 02:15:48 pm
content: If you want to get down to brass tacks, even digital circuitry operates in an analogue world. Slew rates are one parameter that reflects this.

author: MK14
author_rank: Super Contributor
timestamp: September 16, 2018, 02:20:00 pm
content: Quote from: Brumby on September 16, 2018, 02:15:48 pmBut if you want a real challenge. Design this forum, to work, entirely made up of analogue stuff, such as analogue computers and things.Good Luck!Don't cheat and say that digital gates are really 100% analogue circuitry. I know what you mean, but that is NOT what I meant, here.

author: Beamin
author_rank: Super Contributor
timestamp: September 16, 2018, 02:24:10 pm
content: Quote from: MK14 on September 16, 2018, 02:20:00 pmWith through hole transistors that would probably be 100's of square feet. An iPhone out of vacuum tubes would be bigger then LA and consume more power too.

author: MK14
author_rank: Super Contributor
timestamp: September 16, 2018, 02:25:45 pm
content: Quote from: Beamin on September 16, 2018, 02:07:01 pmThey are slowed down by things like slew rate (mentioned above) and other things, such as capacitors (and stray capacitance), taking time to charge up and settle down to the final values.That is why (there is more to it though), op-amps run at megahertz (but you can get some very fast ones), but logic gates can run at gigahertz and faster.

author: Brumby
author_rank: Unknown
timestamp: September 16, 2018, 02:26:10 pm
content: Quote from: MK14 on September 16, 2018, 02:20:00 pmYeah... I know. But somebody had to go there - and I was feeling a little impish tonight.

author: coppercone2
author_rank: Super Contributor
timestamp: September 16, 2018, 02:26:37 pm
content: I think for an analog device thats not switching a logic level an important parameter you are interested in is capacitance. The lead in to the device combined with the capacitance to ground forms a low pass filter which impedes operation.I mean this from a datasheet level view point.For instance if a device has 10pF capacitance to ground, you can calculate the equivalent resistance to see what kind of drive impedance you would need for that circuit, the drive impedance becomes absurd for higher frequencies, if your impedance is like 0.5 because of a capacitor shunting it to ground, your not going to get much energy into the device in the first placefrom there on the specifics probably require you to pick up a transistor physics text book

author: MK14
author_rank: Super Contributor
timestamp: September 16, 2018, 02:30:49 pm
content: Quote from: Beamin on September 16, 2018, 02:24:10 pmGiant analogue circuits, don't really scale up too well. Because the drift and other effects, could mean that it never works, as engineers are forever re-tuning it and fixing it. (Especially old analogue designs, modern stuff can be pretty decent, and solves many of those problems).Even old digital (valve/tube) based computers were like that as well.I think I read that the really old valve/tube, massive computers, could only run for an hour or so (maybe a few hours or so), before another vacuum tube would burn out and need replacing.I think they spent half their time, being repaired and the other half doing stuff (very approximately).N.B. I'm talking about digital computers from the 1940s and 1950s.Later ones became more and more reliable.

author: rstofer
author_rank: Super Contributor
timestamp: September 16, 2018, 02:58:12 pm
content: Quote from: MK14 on September 16, 2018, 02:20:00 pmYou're on!I want to display damped harmonic motion like the mass-spring-damper problem (sort of like the suspension on a car). You start with your digital approach (first principles, not MATLAB) and I'll start patching my analog computer (actually, it's already patched). Don't forget to allow for parameter changes on the damping coefficient and the spring rate. It's fair to assume gravity is constant.Or, change it up a bit. You start with 7400 logic and I'll start with 741 op amps, we'll just breadboard the solution. I need two op amps as integrators, one op amp as a summer and another op amp as an inverter. I also need 3 potentiometers and two timing capacitors for the integrators. Plus a power supply and a hand full of resistors.How's that adder coming along? Actually, it would be fair to use a uC and just write the code. I'll still be up and running first.In my old age, I am finding a lot of fun in playing with the differential equations I struggled with in college.I didn't like all the math required for analog circuits back in school. We had sliderules, the HP35 hadn't been invented and it seemed to me that analog design would go the way of the dinosaur as soon as we had a way to digitize the signals. Not a bad prediction for '72 or so. Even the uC was a pipe dream for a couple of years.I'm not sure younger people realize just how much things have changed over the last 50 years.

author: MK14
author_rank: Super Contributor
timestamp: September 16, 2018, 03:20:59 pm
content: Sadly, I suspect that these (analogue) design skills are being lost. So if we suddenly need them again (and to an extent we do, as they are still needed), it is not so good to lose them.My understanding, is that in the 1960s, there were (relatively) a huge number of Analogue Transistor design engineers, around the world.Who could be charged (excuse the triple pun, as in electrical charge, £/$ charge and charge as in to do things), with making a brand new 20 watt, audio amplifier, completely out of transistors (no ICs or op-amps to be seen/used).These days, people who can design such things, exclusively out of transistors (20 watt amplifier), are getting rarer and rarer.

author: rstofer
author_rank: Super Contributor
timestamp: September 16, 2018, 03:22:21 pm
content: I was just thinking about the difference between an analog and digital approach to controlling the rocket nozzles on the Atlas missile. During launch, the nozzles are used to keep the bottom of the missile under the top. It's kind of important.Which would befastermore responsive? An all analog system where rotation is measured in real time, amplified, integrated, differentiated and/or multiplied and sent to the servos or a digital system where sensors are measured, results computed and finally converted back to voltage and then sent to the servos. Analog integration is a natural result of analog circuits. Differentiation introduces noise and is not often used.That's not to say there aren't applications where digital is more appropriate. What is interesting is the degree to which celestial navigation was used for course corrections. Just a high dollar sextant and a bit of math (probably pre-computed tables). Kind of the ultimate in analog.Once you get outside the uC chip itself, the world is an analog place. Digital doesn't keep that bridge up, analog does. Speed down the highway is really analog. It may show up as a digital indication (+-1 MPH) but the idea that distance traveled is the integral of velocity is actually analog.

author: rstofer
author_rank: Super Contributor
timestamp: September 16, 2018, 03:30:28 pm
content: Quote from: MK14 on September 16, 2018, 03:20:59 pmAnd more expensive, I suspect. I don't know whether companies like Analog Devices have a recruiting problem or not. To some extent, the math skills and basic circuitry are taught in college. Everything else is just on-the-job training. You come in as an enthusiastic new-grad and work with the more experienced engineers to learn the profession. One day you are the experienced engineer.I don't hear names with the recognition of Bob Widlar, Bob Dobkin or Bob Pease (that's a lot of Bobs). There are a number of these guys who really invented the fundamental building blocks for analog design. Now it is simply a matter of step-wise refinement as process capabilities improve.FWIW, here is a brief discussion of the Big Three. Hint, they all worked together at one time or another:https://en.wikipedia.org/wiki/Bob_Dobkin

author: MK14
author_rank: Super Contributor
timestamp: September 16, 2018, 03:33:30 pm
content: Quote from: rstofer on September 16, 2018, 03:22:21 pmFrom a control point of view, that can become a very tricky question. Because the digital computing solution, could attempt to predict (without being 100% accurate), what the control variables are going to be (and need to be), a bit (or longer) in the future.Taking this one step further. Let's say a major control servo, as part of the rockets control system, takes exactly 10 millseconds to respond to changes in requested position.The analogue solution, will tend to respond to changes in the sensors and hence change its output. So the rocket gets its changes 10ms later (because of the servos mechanical delay).But the digital solution, because of its predictions on the near future, can send the new position request to the servo, approx 10ms, before it needs to move, hence removing or reducing the mechanical delay of the servo.But it is possible that a clever/innovative analogue computer solution, could do something similar. With feed-forward (possibly wrong technical name here, what I mean is you calculate it a bit in the future, like a d term in a PID controller, but more sophisticated than that) terms and stuff.

author: MK14
author_rank: Super Contributor
timestamp: September 16, 2018, 03:42:42 pm
content: Quote from: rstofer on September 16, 2018, 03:30:28 pmI'm a big fan of his!I would have loved to have met him. It is a pity he died so young (relatively speaking).He was one of the main developers, of the early IC op-amps.He came up with so much brilliant stuff!If I remember correctly, he had a right hand man, who was hugely helpful for him (possibly a brilliant IC process engineer, which is extremely important). Whose name I have forgotten, and who is often left out of the history.Similar claims are made for the invention of the transistor. Where the leader (William Shockley), took much of the credit. Despite the other two team members, having important roles as well.

author: MK14
author_rank: Super Contributor
timestamp: September 16, 2018, 03:53:59 pm
content: Quote from: rstofer on September 16, 2018, 03:30:28 pmMy understand, is that because in the 1960s, they were doing a huge number of (usually) analogue designs, using discrete transistors. There were lots of analogue design engineers, who day in, day out.Were living and breathing in, analogue designs, and were amongst other brilliant analogue engineers.It was also a time, when doing things like that was very exciting, and people were prowd of such work.Hence the conditions to produce many quality analogue engineers occurred, and it did.But these days, there is considerably less stuff like that done, these days. If you wanted an IC free twenty transistor, complicated analogue system designed from scratch. It would be very difficult to find (especially from the younger generation), people to do it.My understanding is, that it is the design of complicated ICs (other areas as well), which still potentially needs a large quantity of quality analogue design engineers. So a shortage of them, could adversely affect the IC semiconductor industries.

author: rstofer
author_rank: Super Contributor
timestamp: September 16, 2018, 03:58:19 pm
content: Quote from: MK14 on September 16, 2018, 03:42:42 pmI had lunch with Bob and a bunch of his cohorts one time when I worked for National. He spent a lot of time in Puerto Vallarta kicking back and thinking about new stuff. And then there is the story about the lawn out front of National's first building. They didn't have money to pay a gardener so Bob bought a sheep (not the rumored goat). Problem solved!Bob Widlar was a unique individual. I didn't meet the other Bobs but I did meet Charlie Sporck one time.https://en.wikipedia.org/wiki/Bob_Widlar

author: rstofer
author_rank: Super Contributor
timestamp: September 16, 2018, 04:04:37 pm
content: Quote from: MK14 on September 16, 2018, 03:53:59 pmBut why would you use an all-transistor design these days? We don't still use the CK-722 Germanium transistor and not many new designs will use a 741 op amp. Things change...The analog companies are all still in business making new devices all the time. The engineers wouldn't design a circuit using all transistors because there is no motivation for doing so. But I don't doubt for a minute that they could do it.

author: Ducttape
author_rank: Regular Contributor
timestamp: September 16, 2018, 04:31:14 pm
content: When I was a kid you could spin the channel knob on the TV as fast as you wanted and still see, ever so briefly, the image/video of each channel for that fraction of a second it was selected. I miss that.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 16, 2018, 04:33:39 pm
content: I imagine you will still find analog control systems in use today. As mentioned, digital is still analog. Speedwise, seems like the same problems will haunt both.A few of us were playing around with some simple oscillators some time ago.https://www.eevblog.com/forum/projects/el-cheapo-oscillator/I was playing around with some old 7400 logic making ring oscillators. How times have changed.https://www.eevblog.com/forum/projects/waveforms-in-a-74ls04-ring-oscillator/

author: MK14
author_rank: Super Contributor
timestamp: September 16, 2018, 04:36:59 pm
content: Quote from: rstofer on September 16, 2018, 04:04:37 pmActually, the answer to that question, is quite simple.I don't know the latest world wide figures, as to how many of the following designs, still need to be created.But there is a need to design new ICs (ASIC's, full custom ICs and similar such things), for all sorts of application areas.E.g. A new sensing technology is invented, and it is expected to sell and be produced in the tens of millions each year.Perhaps a new acceleration/motion detector, for the latest games console controller or virtual reality or car sensors etc etc.That may need one or more, brand new designed, fully custom (or similar) all analogue ICs to be designed.No op-amps or digital gates on it at all. Just 20 (or 5 or 50,000), cleverly placed analogue transistor designed, circuits.So in order to design this new, all analogue (transistor) IC. It needs, clever, experienced analogue design engineers to create it.Even if it goes to an all analogue design, but uses op-amps, via an IC ASIC design. It still needs analogue designers to create it.Also, there are plenty of mixed, analogue and digital, custom ICs. Sometimes including MCUs.The analogue bits, still need analogue designers, even if the onboard MCUs needs other types of engineers (software etc).

author: rstofer
author_rank: Super Contributor
timestamp: September 16, 2018, 04:53:33 pm
content: This kind of design is being done all over the world! There is no shortage (that I know of) of people capable of designing the chips. It's a learnable skill and the design rules are pretty well documented. Particularly in the case of ASICs where the final design is just an assembly of standard cells.OTOH, I couldn't imagine making a 16 bit full adder from transistors. And why would I? I can just plunk down a pre-built IC and call it good. I probably wouldn't even do that! I would just use a CPLD or FPGA and write a line of code to instantiate the adder.

author: coppercone2
author_rank: Super Contributor
timestamp: September 16, 2018, 04:55:24 pm
content: the difference between digital and analog is the initial comparator, then its just an analog signal but in the frequency/timing domain only. You still get noise but in the time axis and of course duty cycle.You also get things like noise margins that are different in different parts of the circuit and stuff like that, voltage levels will be different in different parts, but so long it works no one really cares, but you can design the shit out of it just like anything else... even the IC has some kind of specification throughout its signal routing.. its not really magically stable or something, and this all comes down to analog design choices that are made, the digital most people are used to is just idiotproofed very well so it seems invariant compared to digital design. Most people won't care past a specification like fanout.You can persue specs like noise related effects (stability, margins,thresholds), propagation delay (stability), jitter stability, power consumption,in anything engineering the only reason you are happy with off the shelf parts is that they meet your expectations. They can always be built differently to conform to a different standard or design choice you choose for whatever reason, its just hardly economical to pursue the benefits of things like custom digital memory, but it irritates me none the less.

author: coppercone2
author_rank: Super Contributor
timestamp: September 16, 2018, 05:08:55 pm
content: Quote from: rstofer on September 16, 2018, 04:53:33 pmbecause you don't have a specification that requires it yet

author: james_s
author_rank: Super Contributor
timestamp: September 16, 2018, 06:11:41 pm
content: Quote from: MK14 on September 16, 2018, 03:20:59 pmI think they are. A while back when I found myself looking for work and toying with going more toward hardware rather than the software work I'd been doing I interviewed at a place that makes automated testing systems. They said they normally hire fresh EE grads but had been disappointed in the lack of analog skills in people coming out of the universities. As a college dropout almost entirely self taught hobbyist engineer I wasn't expecting much and I actually preemptively turned down the position because the commute would have absolutely killed me and I knew going in that it would have meant a pay cut but they told me later I was easily the most qualified person they talked to.Ultimately I decided to stay in software which tends to pay a lot better, and keep EE as a hobby. It's something I enjoy doing enough that I don't want to turn it into work. Anyway the point of all this is that if my analog abilities which while passable are not expert level are that much better than recent EE grads then analog is in trouble.

author: technix
author_rank: Super Contributor
timestamp: September 16, 2018, 06:21:46 pm
content: I have this feeling that the Moore law disproportionately applies to the digital domain, driving the cost of digital circuitry down way faster than analog circuitry. For now even when digitally-generated analog signals are used (for example those LVDS and SerDes systems) it is way too often building redundancy into the digital domain, allow analog problems to happen, and happily mask the problems.Digital circuitry does have the benefit of wide-open gaps between VIL and VIH allowing the circuits to work with little to no trimming driving yield up.

author: MK14
author_rank: Super Contributor
timestamp: September 16, 2018, 06:23:08 pm
content: Quote from: james_s on September 16, 2018, 06:11:41 pmMy opinion, understanding and beliefs/experiences are that QUANTITY wise, we may well have enough analogue engineers.But the thing is, quality/ability/experience levels do vary. So, although we hopefully have the quantity, we don't necessarily have many/enough of the really high calibre analogue design engineers.This might matter. Perhaps because we need them, to hopefully compete well in the west, against the upcoming likes of China (and other countries).There could even be wars again, one day. Electronics will then be an extremely important part of such wars. Even during World War 2, electronics was extremely vital (Enigma decoding computers in the UK, Anti-aircraft proximity fuzes, anti-ship fuzes, artillery proximity fuzes, RADAR, Radios/Transmitters etc etc).Even our respective countries economic success or not, could be affected, by the electronics industries and stuff.So I think it is very important.But also, Digital Electronics (few know how to do complex FPGA (VHDL, Verilog) designs), software engineers, etc etc.

author: james_s
author_rank: Super Contributor
timestamp: September 16, 2018, 06:28:43 pm
content: Quote from: Ducttape on September 16, 2018, 04:31:14 pmYes, channel surfing is a painful experience these days, although between the increased ad load, network logos and vastly reduced quality of the content, TV in general is a painful experience these days so perhaps it doesn't matter.I'm reminded of when we were kids, my best friend in elementary school figured out he could turn the knob on the cable box in between 18 and 19 and wedge it there with a matchbook and the Playboy channel would come in. His parents always seemed to get home just a few minutes after we got it working though.

author: rstofer
author_rank: Super Contributor
timestamp: September 16, 2018, 07:19:41 pm
content: Quote from: james_s on September 16, 2018, 06:11:41 pmEverybody works in their own self-interest. At the moment, it is a given that software pays more than hardware and that digital hardware pays more than analog hardware. There are also more jobs available in software than in digital hardware than in analog hardware. And the math is harder for analog design...No student that has even looked atwww.bls.govwould bother studying analog design and, truth be known, even digital hardware design is questionable. Job openings and pay scale trumps everything.So the analog companies have to expect to do a little on-the-job training. All of the other companies do the same thing. I doubt that any new-grad grasps the complexity of the latest Intel designs regardless of how well they did in hardware and computer design courses.

author: coppercone2
author_rank: Super Contributor
timestamp: September 16, 2018, 07:27:05 pm
content: does an analog designer at least physically move more then a digital one (big perk of the job)?

author: joeqsmith
author_rank: Super Contributor
timestamp: September 16, 2018, 07:46:16 pm
content: Quote from: james_s on September 16, 2018, 06:28:43 pmAds pushing the latest drugs and ads for attorneys going after the old drugs... I gave up on TV years ago. I don't even watch the news (if you want to call it that) anymore.With the push for digital I wonder as a public service system, how well it would even work now. The analog systems were very robust. The digital systems seem the complete opposite.

author: Zero999
author_rank: Super Contributor
timestamp: September 16, 2018, 07:49:04 pm
content: Quote from: MK14 on September 16, 2018, 02:30:49 pmYes, no modern digital IC will perform well if built from discrete components, because the physical distances between the components would make the propagation delays too long for it to work at a reasonable speed.

author: tggzzz
author_rank: Super Contributor
timestamp: September 16, 2018, 07:59:49 pm
content: Quote from: Brumby on September 16, 2018, 02:15:48 pmExcept in the photon counting and femtoamp domainsBut otherwise you are right; "digital" is merely aninterpretationplaced on an analogue value.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 16, 2018, 08:10:58 pm
content: Quote from: tggzzz on September 16, 2018, 07:59:49 pmI would assume it was still all analog.

author: tggzzz
author_rank: Super Contributor
timestamp: September 16, 2018, 08:17:56 pm
content: Quote from: joeqsmith on September 16, 2018, 08:10:58 pm1fA is 6424 electrons/second. At that rate the electrons can be individually counted therefore they "are digital".

author: coppercone2
author_rank: Super Contributor
timestamp: September 16, 2018, 09:15:39 pm
content: their speed sure aint digital, unless you got some idea about plank limits

author: james_s
author_rank: Super Contributor
timestamp: September 17, 2018, 03:55:22 am
content: Quote from: rstofer on September 16, 2018, 07:19:41 pmThat's not always true. My other half manages a veterinary clinic. She could make roughly twice as much doing the same job managing a human medical clinic but chose the job she has because she loves working with animals. A good friend's wife has a masters in chemical engineering and was making a good living as a software developer, she recently quit to become a teacher because doing something she wanted to do trumped the much larger paycheck. Being the primary earner in my household though it was a fairly easy choice to go with the higher paying job, I can do the hardware as a hobby and probably enjoy it more than I would if I were doing it for a living anyway.

author: BrianHG
author_rank: Super Contributor
timestamp: September 17, 2018, 04:21:00 am
content: Quote from: Ducttape on September 16, 2018, 04:31:14 pmThis was my favorite CATV converter, even kept it after the numeric display wireless remote ones became available.You can slide through all 42 channels, TWICE!, in 1 second!Jump from any 1 channel to any other in under 0.25 seconds without numeric entry on a remote...Excellent for jumping channels and avoiding commercials.

author: radioactive
author_rank: Regular Contributor
timestamp: September 17, 2018, 05:27:14 am
content: Shortest distance between two points is a straight line, so I think analog might win this one with quantum tunneling...Quote

author: BrianHG
author_rank: Super Contributor
timestamp: September 17, 2018, 06:19:44 am
content: Screw digital, this analog vacuum tube runs circles around digital ICs...https://www.extremetech.com/extreme/185027-the-vacuum-tube-strikes-back-nasas-tiny-460ghz-vacuum-transistor-that-could-one-day-replace-silicon-fetsBuild some integrated structures in it to create something like an op-amp or mixer, and you can compare/add/sub in the linear analog domain much faster than digital silicon.

author: Brumby
author_rank: Unknown
timestamp: September 17, 2018, 07:38:17 am
content: Quote from: tggzzz on September 16, 2018, 07:59:49 pmI was waiting for someone to go there.Congratulations!

author: tggzzz
author_rank: Super Contributor
timestamp: September 17, 2018, 07:45:21 am
content: Quote from: Brumby on September 17, 2018, 07:38:17 amYeah well, it had to be me, didn't itSometimes I like to enliven fairly ill-defined debates with points that stretch people's imagination and understanding

author: petert
author_rank: Regular Contributor
timestamp: September 17, 2018, 08:29:56 am
content: Quote from: tggzzz on September 16, 2018, 07:59:49 pmInteresting. Could you elaborate on that, considering I am not an expert? Would that affect aliasing/filters?Would be great if these effects could be simulated on a discrete element basis (discrete time/charge carriers).

author: Zero999
author_rank: Super Contributor
timestamp: September 17, 2018, 10:42:45 am
content: Quote from: petert on September 17, 2018, 08:29:56 amBecause electrons are discrete particles, one could argue that their presence or absence is binary, i.e. digital, but it's still analogue, because the number of electrons over a certain time period isn't just a 1 or 0 value. Of course one could then argue that at very low currents or short time periods, the answer will then be 0 or 1 but at that point it's just noise. Longer time periods are required to get a meaningful current reading.Compare this to counting the number vehicles per hour in a single lane of traffic. When there's not much traffic or over short periods of time, the answer will always be either zero or one, tending towards zero for shorter time periods and quite periods. In the rush hours, it may be acceptable to count the number of vehicles over a 10 minute period, multiply it by six and get a reasonably accurate estimate at the number of vehicles per hour, but counting over a shorter periods or when it's less busy, the result will become progressively less accurate.This above is an example of shot noise and which is why a long exposure time is required to get a good image, at lower light intensities and it's impossible to measure tiny currents, at high frequencies, with any decent accuracy.

author: tggzzz
author_rank: Super Contributor
timestamp: September 17, 2018, 11:43:12 am
content: Quote from: petert on September 17, 2018, 08:29:56 amRealise that all digital information is transmitted by analogue voltages (or currents, but I'll ignore that for simplicity). The voltages depend on the logic family, with 0-5V, 0-3.3V, 0-1.8V being typical limits.Examples...A TTL (not CMOS) input will consider any input voltage above 2.0V or below 0.8V to be valid logic levels. If you look at a TTL high output on a scope, you can see it vary between (say) 2.6 and 3.6V depending on the state of all the devices inputs - but that doesn't matter provided the receiver "sees" a voltage above 2.0V. The receiver regards/interprets/thinks anything above 2.0V as a logic high.Many digital systems are not binary, but have multiple levels and phases. That's how you can transmit, say, 56kb/s down a telephone line with an 8kHz bandwidth; the baud rate is <<56kHz!Have a look at transmission line theory for modern fast risetime digital logic families. The voltages seen "on the wire" can have several different values as the signal moves from transmitter to receiver, and those are very much dependent on the source and receiver termination strategies used.

author: rstofer
author_rank: Super Contributor
timestamp: September 17, 2018, 02:49:01 pm
content: Quote from: james_s on September 17, 2018, 03:55:22 amAs long as the total household income is sufficient, it is possible to walk away from the highest paying opportunity. But there is no point in working your way into poverty. There are easier ways to get there.I always kept electronics as a hobby and never did work in the field. I made a decent living working essentially in project management.

author: petert
author_rank: Regular Contributor
timestamp: September 17, 2018, 04:07:19 pm
content: Quote from: tggzzz on September 17, 2018, 11:43:12 amThanks, informative as well. Though, I was thinking of an answer more along the lines of Hero999.I wonder how the transition between discrete/digitial and continous/analog happens.QuoteWhy would you get noisy results, isn't it possible to count individual photons, for example?Assuming a noisy reading, I see we are talking about average currents/voltages, so measuring over a longer/reasonable time period to average out fluctuations.But if in theory your sampling frequency would be high enough, you'd get discrete electron counts, right?Assuming that is possible, is then analog really nothing more than averaging over many discrete measurements (either deliberately by later mathematical averaging, or implicitly by measuring over longer time periods)?

author: Zero999
author_rank: Super Contributor
timestamp: September 17, 2018, 05:30:14 pm
content: Quote from: petert on September 17, 2018, 04:07:19 pmYes, at high sample rates you'd get electron counts, the same for photographs at high shutter speeds getting discrete photon counts.It's noisy because of the discrete nature of the electron/photon. 1fA is 6242 electrons per second, so suppose we measure exactly 1fA flowing in a piece of wire over a period 1ms, there's no way we can get any level of accuracy beyond 1 in 6.242. If we kept repeating the measurement, the reading would fluctuate considerably, seemingly at random. Only when thousands of samples are taken would be know for any certainty we have exactly 1fA flowing, rather than 0.9fA or 1.1fA. Now that's fine at DC, but if the signal is AC and non-repeating, there's no way to separate the information from the random fluctuation in the number of electrons passing per ms.This is why photographs taken with too shorter shutter speed, when there isn't enough light appear grainy and our vision in low light is blurry. A long exposure time is required, at low light level, with a very large lens, to get a high resolution image.

author: BrianHG
author_rank: Super Contributor
timestamp: September 17, 2018, 05:32:39 pm
content: Problem: as transistor size decreases, system voltage decreasing, wont we reach the near bottom voltage switch point where the so-called digital switches are acting at their edge of on-off state, sort of like being in the analog domain. Or will quantum tunneling make such digital IC too noisy to function at all?

author: tggzzz
author_rank: Super Contributor
timestamp: September 17, 2018, 06:04:39 pm
content: Quote from: petert on September 17, 2018, 04:07:19 pmThere is no transitionThe discrete/digital domain is merely aninterpretationof the analogue domain.However, it is possible to define analogue circuits thatmainlystay within separate bounds and not in the "gap" between the bounds. But they sometimes fail to do that; a classic example is a flip-flop in a metastable state.Consider a couple of bipolar transistors connected as a "long-tailed pair". Depending on the voltages applied to the transistor bases, the LTP can act as a linear differential amplifier, a mixer, an ECL logic gate, a multiplier, a current switch, etc...

author: Circlotron
author_rank: Super Contributor
timestamp: September 18, 2018, 02:14:19 am
content: Designing simple analog circuits with opamps is like writing code in BASIC.Designing simple analog circuits with discrete transistors is like writing code in assembly language.

author: MK14
author_rank: Super Contributor
timestamp: September 18, 2018, 02:28:41 am
content: Quote from: Circlotron on September 18, 2018, 02:14:19 amDesigning simple analog circuits with discrete valves/tubes is like writing code in raw binary (0110101110)Designing simple analog circuits with discrete passives is like writing code in DOSDesigning simple analog circuits with discrete gunn diodes is like writing code in microwave machine code

author: Beamin
author_rank: Super Contributor
timestamp: September 24, 2018, 12:07:40 am
content: Quote from: radioactive on September 17, 2018, 05:27:14 amI think that's because they are not traveling but rather going out of and back into existence at a different part of their probability wave. I think the double slit works because the instant a particle is created its probability wave fills the whole universe instantly. When a proton is formed it doesn't grow from a point and spread out to its diameter or quark for that matter so why should its probability wave have to grow at the speed of light? When you make something, anything appear you have a chance that it is not going to be somewhere else. So at some level its probability of existing or not existing is everywhere.

author: tpowell1830
author_rank: Frequent Contributor
timestamp: September 24, 2018, 04:53:25 am
content: Hmmm, when I was a young man, I was a cowboy. I had a pickup truck in which I would haul hay out to the cows in the winter time. My pickup truck had 325 horsepower. The problem was, when I hauled hay to the cows, it was wintertime and the cows were in the pasture deepest in the ranch. In order to get to this pasture I would drive down dirt trails and every so often I would have to stop at the next pasture and get out and open a gate, drive through, then get out and go close the gate behind me. There were 4 or 5 pastures between me and the cows. It only took a minute or so to get through the pastures, but at least a minute to open the gate and drive through and close each gate.When I emptied all the hay from my truck for the cows, I got back on the open highway, I could go as fast as I wanted because there were no gates.