# Phase shift

• posted

Hello , i am trying to combine or mix three signals with the same frequency together in one channel. i have no idea hw i can do that. The signals are sin waves. I think if i chnaged the phase of each one and then combine them together it will work. but i have no chip to circuit to implement that. could u plz suggest me something this is my email also

snipped-for-privacy@Ewi.twente.nl thanks

• posted

It's not at all clear just what you are trying to do.

If the 3 signals are sine waves of the same frequency, they will add up vectorially to produce a single sine of that same frequency. Depending on their relative phases, the amplitude of that sine may be anything from zero to the sum of the input amplitudes.

If that maximal amplitude is what you are looking for, you have to insure that all 3 waves are in phase. If they do not originate from the same source, it may be rather difficult to adjust the phases since they will tend to drift. If they *do* originate from the same source,

but have passed through independent phase-shifting paths before you sum them, then adjustable phase shifters may do the job.

Perhaps if we knew what your ultimate goal was, we could suggest the best approach. For example, if you are trying to measure total amplitude, it might be simpler to rectify and filter each sine separately and then sum them as DC.

Best regards,

Bob Masta DAQARTA v3.50 Data AcQuisition And Real-Time Analysis

Scope, Spectrum, Spectrogram, FREE Signal Generator Science with your sound card!

• posted

Why do you wish to do this, and in what way do you wish to combine the signals?

If you are planning on simply adding them, and you want to use them to communicate three different channels, then you'll find you're out of luck. With a perfect phase reference (which generally requires a second channel anyway) you could put two quadrature signals on a wire and decode them at the other end - but you'd need that second channel.

Could it be that you have three signals that fall into the same frequency _band_ that you wish to multiplex onto one wire? If so, tell us and we'll have some suggestions. If not, tell us what you're really trying to do.

```--
Tim Wescott
Wescott Design Services```
• posted

hello, Actually, i have 3 signals as a sine wave from different sources as a measured quantities from 3 different sensors. i want to transmit these signals in the same channel. if i just added them it will be added together. what i want is to tranfere these signals in the same channel. Is that possible to do by delaying (adding different phse shift) each signal with different time delay. Knowing that i don't want to use analog multiplexer (time division multiplexing). If the phase shift is ok...do we have a circuit to do that except (All pass filter or the SAD chip).? thanks

• posted

That's not possible. Phase shifting only gives you two degrees of freedom, and then only if you have a solid phase reference.

You need some form of multiplexing. I'm not sure why you don't want to use time division multiplexing, but it may be the way to go; if your signals aren't too high in bandwidth and your accuracy requirements aren't too severe then it's not that difficult. The range of possibilities are endless; two analog methods that spring to mind are frequency-division multiplexing, by heterodyning your signals up in frequency at the transmitter and down at the receiver, or amplitude-modulating some carriers with your signals at the transmitter, then filter/detect the signals at the receiver.

This is 2008: the best way to do this in many ways is to encode your signals digitally as close to the sensor as you can, then send them over a network. Even if all you do is regenerate them back into analog at the other end, digital is getting easier and easier with respect to analog every day. Without knowing your situation I can't insist that this is the best way, but you shouldn't discard it as a possibility.

```--
Tim Wescott
Wescott Design Services```
• posted

very day. =A0Without knowing your situation I can't insist that

According to your answer i have to explain my case in more details. I have a 4 x 4 array of capacitive sensors. I have already used Frequency Division Multiplexing (FDM) with different frequencies to excite the capacitive sensors for each colomn. The output of the sensors are the common rows of the matrix. Therefore, each row in the matrix consists of 4 signals with different frequencies. The output signals now are AM modulated signal which have frequencies as the carrier frequency (1 Mega HZ to 4 Mega HZ). At the output side, i want to combine all of the signals of each row just in one wire in such a way that transmitting the signals will be easier and less hardware i can use. I am thinking of adding some time delay in each row different from the other rows. Another idea i have is to do AM modulation again (frequency shift) to higher frequencies. But the later choice is little bit difficult because i have already high frequency signals and i don't want to go higher which will cost me more expensive hardware. i am now stucked at this point. otherwise, i have to make for each row its own detection and ADC circuits. For higher order arrays, this will be difficult and more hardware i have to use. On the other hand, using time multiplexing and analog multiplexer will affect the bandwidth of the sensors and decrease the measuring time therefore, less SNR. Hope this is clear and hope to get an idea for this. If the phse shift will work, plz let me know if any chip is available with these high frequency signals.

• posted

toanalogevery day. Without knowing your situation I can't insist that

There are very few commercially available chips that are designed to do things that are technically impossible. Those that are designed so usually aren't commercially successful.

Please read my last two answers on why using phase shift just won't work. If you don't believe me, get out a pencil and some paper and study the behavior of sine waves.

I suspect that the bandwidth of the actual signal you want is significantly lower than the bandwidth of your carriers. You may find it very worthwhile to find a way to reduce the carrier/bandwidth ratio; this will allow you to pack more information into a pair of wires that are good to some maximum frequency. You may also find that the best way to do this is to move your ADC/demodulate step close to the sensors, so that you can send the data digitally for the long distance.

```--
Tim Wescott
Wescott Design Services```
• posted

• posted

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ogevery day. =A0Without knowing your situation I can't insist that

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text -

I beleive that the phase shift is not working.if the delay is small..but what i am thinking in that to delay the signal with a time equal or little bit more than the bandwidth of the first signal...it is just kind of Time Division Multiplexing (TDM) but without loosing any information from the first signal by using the traditional analog multiplexing techniques...using the ADC in the early stages will not be the best choice..because the amount of the hardware which should be used...regarding the demodulation..i wanna to use DSP processing to recover the signals and not the traditional way in using demodulator....

• posted

The simplest solution (given what you have so far) would seem to be time-division multiplexing, where you connect each row to the output line in sequence. The problem then is telling which position the multiplexer switch is in at any given moment. You could add a DC signal (or another frequency) that encoded the switch position. (Or, if you insist on doing something with phase, you could phase shift each row differently... ugh!)

There are capacitive array sensor chips that are designed for touch panels and the like. You won't get continuous output from each sensor, but rather the chip's estimate of where the touch point is. If this is what you need to do, the interfacing will be much simpler.

Best regards,

Bob Masta DAQARTA v3.50 Data AcQuisition And Real-Time Analysis

Scope, Spectrum, Spectrogram, FREE Signal Generator Science with your sound card!

• posted

OK, that's easy. First, you need to isolate the combined signals from the sensor matrix outputs (so, this is a job for ... an amplifier). The combination can be a simple summing junction (four amplifier outputs connected to the summing point).

Four one-transistor amplifers, with their collectors all joined to a single pullup resistor, and some base and emitter biasing, will do it. If you wish, a signal transformer at the collector can be useful (its the easiest load/level-translation solution for your output, and at 1 MHz needn't be an expensive component).

• posted

If they are true sin waves then you could just take the amplitudes and put them through an orthogonalization process.

f(x) = A1 + x*A2 + (3*x^2 - 1)/2*A3 is unique.

This is the legrendre orthogonal polynomials.

You basically sweep through x from -1 to 1 sending f(x) as the signal.

You can then recover A1,.., A3 by the orgonalization properties. (requires an integrator)

This is not necessarily the best way but I think it could potentially be done with just passive components and maybe a few transistors and/or op amps.

Probably easier just to frequency shift the signals and then filter them back out or simply time domiain multiplex them.

You won't be able to simply add them directly because there is no way to exact them back out of the sum. Its like if you take 3 + 3 = 6 then try to recover what was added to get 6. It doesn't work cause there are an infinite number of ways to do it and not just 1.

I think though simply exacting the amplitudes(pretty easily done) and send them in some way, even a asynch serial like protocol would work fine.

For example, simply send the amplitude of the first, then ground the line, the amplitude of the second, ground the line, and the amplitude of the third, then ground and repeat.

_____ | | _____ _____ | | | | | | | | | |

---+ +---+ +---+ +---

The only issue is if they get out of sync but this I think you could throw something together with minimal components here. (just a mux/demux, a clock, and some passives)

• posted

no..this is different. I want to get flow measurements by varying the capacitance value. it is some hw a designed structure.

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