Time Shift???

[raviram87]

Hi people.... is there any circuit or IC that can time shift a given analog signal???

i.e., say that a analog signal starts at the origin and continues.... can i shift this signal alnog the time axis and make it start from a point say t2 distant DELTA T fom the origin....

is this possible with any IC??? if so, please mention it... or is it realizable using some circuit??? PLEASE HELP ME OUT!!!

 

[Nigel Goodwin]

You need to specify what the analogue signal is, and how long it needs delaying - there are various ways to do it, most of them digital these days.

 

[raviram87]

let the input signal be any periodic waveform... sine wave, square wave... or any periodic sequence for that matter..... and assume that the input signal level amplitude is +5V and -5V.....

i want to shift the above waveform by some small amount, say, DELTA T..... can i not control this value of DELTA T????

 

[Nigel Goodwin]

As I said before, you need to specify the exact requirements - or is this just a question at university?.

 

[ThermalRunaway]

You can buy delay lines which delay a signal by a given time, or you can use a DSP to do that sort of thing, but obviously that last option is very complicated.

Like Nigel says, you need to properly explain what it is you're trying to do. What sort of signal are you hoping to time shift? What sort of amplitude is it? What type of signal is it? What's the frequency range? And most importantly, WHY are you trying to time shift it?

If you really are trying to time shift a signal, you should be able to answer these questions. And, if you can answer these questions, we should be able to answer yours!

Brian

 

[raviram87]

k.... this is in relation to a circuit that we are building for a competition.... the competition is about building a circuit for determinig the frequency of an incoming periodic signal....

all that is mentioned about the signal is that it is periodic and can have multiple zero crossings in the same period.... our idea is to time shift this signal by small amounts of time DELTA T and keep on comparing the original signal with the time shifted signal....

by this method at some instant of time T=sum of all small time shifts DELTA T the comparator output will be zero.... so that T is the Period of the incoming signal and hence we can determine the frequency....

Its not a univeristy question or something.... the above things are why we want to do with this.... i have attached one signal for reference.... if this is the input signal given, then how to shift it from the origin, i.e., along time axis??? thats what i want...

 

[ThermalRunaway]

Hmmm. Well, the best idea I can think of - but you'll have to have a good think about it to decide if it's going to work - is this:

Feed your input signal into a mixer. The mixer output is then fed to a PLL IC, and the PLL IC tunes a VCO. The output of the VCO is fed back into the other input of the mixer so that the PLL locks to the input signal and tunes the VCO until the output of the mixer is zero. This will work as follows: When you apply an input signal to the mixer, the output of the mixer will initially be the input frequency minus (or plus) the VCO frequency. If this is not zero, the PLL will tune the VCO until the output from the mixer = 0. Once locking has occured, you can measure the frequency of the VCO using a simple counter and this will give you a measurement which is proportional to the input frequency.

I'm not sure this idea will work exactly the way you want it to, and it's going to end up more complicated than I've explained, but it sounds a bit easier than your original idea to me!

Brian

 

[ThermalRunaway]

Actually, I'm just wondering if that idea would work. It probably would for sine/triangle/square wave signals but not so sure about complex waveforms like the one you've shown. Can anyone else offer some advice on this?

Brian

 

[ThermalRunaway]

I've been thinking more about this. What you really need to do is find out the fundamental frequency and measure that, as any other signal content is merealy added to the fundamental and does not change it's base frequency. I wonder if you could filter out all of the harmonics??

Brian

 

[ThermalRunaway]

There's a frequency meter featured as a project in this month's edition of EPE. If you don't get EPE where you are (you don't specify a location), you can normally buy the articles online at their website.

Brian

 

[raviram87]

hmmm.... am from bangalore in india.... i dont think that magazine is available here.... anyway i will try to buy the article online.... thanks.... and please do help me out people with this.....

 

[raviram87]

hello people.... is there no other way in which i can implement my idea??? any circuits for measurin the frequency of an incoming periodic signal??? the ampplitude range of the signal is in the limit +5V and -5V.... and the frequency range i want to measure is of the order of 100Hz to some KHz... cant construct this using any simple components??

 

[ThermalRunaway]

It's certainly not going to be done using merely simple components, but it's a "doable" project. I'm more a digital than an analog person so I'm sure there are others on here who could suggest better ideas than me. Did you look into my PLL idea?

Brian

 

[Nigel Goodwin]

hello people.... is there no other way in which i can implement my idea??? any circuits for measurin the frequency of an incoming periodic signal??? the ampplitude range of the signal is in the limit +5V and -5V.... and the frequency range i want to measure is of the order of 100Hz to some KHz... cant construct this using any simple components??

As I've repeatedly said, you need to say EXACTLY what you're trying to do (and why), vague replies about 'periodic waveforms' are completely meaningless. Either it's a homework question phrased like that, or it's for a specific reason - it's the reason we need to know.

 

[raviram87]

its not any home work.... we are supposed to design this circuit for a competition.... the competition goes like this....

the organizers will be supplying us a continuous analog periodic waveform in the amplitude range +5V and -5V generated in their lab through a wire to the circuit we design.... the waveform need not be necessarily sinusoidal or any known periodic shape.... it can be complex waveform also like the one i have attached in one of my previous posts.... the signal can have multiple zero crossings within the same period also...

when such a signal is given, we have to design a circuit that can take this signal as input and display the period of that signal on a 7 segment display unit....

higher the range of frequency our circuit can measure we get more points.... we are not supposed to use any DSP processors(and i do not know about them also).... if our circuit functions purely in the analog domain, we get more points.... if we do not use a microcontroller, we get more points(i know only basics of PIC)....

That is why am on the lok out for such circuits.....

 

[ThermalRunaway]

As I've repeatedly said, you need to say EXACTLY what you're trying to do (and why), vague replies about 'periodic waveforms' are completely meaningless. Either it's a homework question phrased like that, or it's for a specific reason - it's the reason we need to know.

Has he not already done that? He wants to design a circuit which will measure the frequency of a periodic waveform. The waveform can have multiple zero crossing points, so could be a complex wave. He has an idea based around time shifting the signal and continuously comparing it.

What more information can he give?!

Brian

 

[raviram87]

we are a batch of 5 students working on this.... second year undergrad students... so we do not know bout some tough methods....

this idea of continuously shifting the signal came to our minds while we were discussin... but we do not know how to implement it.....

please help us out in this!!!

 

[Nigel Goodwin]

Has he not already done that? He wants to design a circuit which will measure the frequency of a periodic waveform. The waveform can have multiple zero crossing points, so could be a complex wave. He has an idea based around time shifting the signal and continuously comparing it.

What more information can he give?!

Basically what it's for! - which he's now done, telling us that it's not an actual project, but a poorly specified assignment!.

From the waveform he posted, it looked like it may have been for tuning musical instruments - which is a fairly common request.

 

[raviram87]

k... you are viewing it as an assignment.... let it be that way.... the fact is we do not understand how to go ahead with it.... in fact its the first time we are doing something practical..... all that we have been doin so far is studying theories of how transistors, opamps, diodes etc... work...

now we do not know what we have to use to implement this....

can you please help us out now, as you know for what we are trying to do this??? and infact what we are teying to do!!! nothing related to guitar tuning or stuff like that....

the organizers will be giving us waveforms similar to the ones i have shown... it will be supplied to us through a wire.... that will be the input to our circuit... our circuit has to display the period of this waveform on a 7 segment display!!! we came up with this idea of time shifting the signal and comparing it with the original signal.... but we do not know how to implement it....

 

[Nigel Goodwin]

k... you are viewing it as an assignment.... let it be that way.... the fact is we do not understand how to go ahead with it.... in fact its the first time we are doing something practical..... all that we have been doin so far is studying theories of how transistors, opamps, diodes etc... work...

It's an 'assignment' in that it's not a practical project that you want, and the task has been 'assigned' by a third party.

now we do not know what we have to use to implement this....

can you please help us out now, as you know for what we are trying to do this??? and infact what we are teying to do!!! nothing related to guitar tuning or stuff like that....

the organizers will be giving us waveforms similar to the ones i have shown... it will be supplied to us through a wire.... that will be the input to our circuit... our circuit has to display the period of this waveform on a 7 segment display!!! we came up with this idea of time shifting the signal and comparing it with the original signal.... but we do not know how to implement it....

It's not a method I've ever heard of, and I've no idea if it would work - but it's also not a trivial task in the first place!. Years ago there were devices called BBD's (Bucket Brigade Devices), these could be used to create fairly simple short analogue delays - often used for guitar effects, such as flanging and reverb. These have been obselete for many years, and the modern method is to digitise the signal and store it in sequential memory, you then read it out again somewhat later, this gives a time delay.

But in BOTH cases you need an accurately specified frequency range, which is crucial to the design - the higher the frequency range the more complex the delay system becomes. You also require low-pass filtering on both the input and output, this prevents various nasty effects from anti-aliasing.

Your requirement for only 'simple' components also makes it far harder, if even possible?.

From the information given so far it sounds an extremely difficult task, unless there's more given in the rules that you haven't mentioned?.

Assuming the waveforms are EXACTLY as shown?, and never any different?, you could simply slice the tops of the waveform (use a comparator) - this will give you a simple pulse sequence of the frequency you need to measure. Use these pulses to gate an oscillator feeding a digital counter - first pulse resets the counter and opens the gate, the next pulse closes the gate - the oscillator frequency is chosen for the resolution you require, and is also dependent on the frequency you're measuring. But even this simple solution isn't trivial!.