Phase shifter vs TTD (delay)

[ktr]

I am currently working on a TTD component for some radar application; but I'm a bit confused about the difference between a phase shifter and delay component. Ain't they should be same since phase difference is also a time delay in essence.

 

[KlausST]

Re: Phse shifter vs TTD (delay)

Hi,

the phrase "phase shifter" in my eyes can be applied to a single sine frequency only. It often means a (signal frequency independent) fixed phase shift. Like 20°

Whereas a "delay" is more related to a digital signal, maybe even discontinous. It often means a (signal frequency independent) fixed delay time (not phase angle). Like 10ns

In audio equippment (I know this doesn´t necessarily apply to RF) "delay lines" can handle random signal waveform.

Klaus

 

[ktr]

Re: Phse shifter vs TTD (delay)

In audio equippment (I know this doesn´t necessarily apply to RF) "delay lines" can handle random signal waveform.

Klaus

Thank your for replying, Can you elaborate on what you mean by handling random waveforms?

 

[KlausST]

Re: Phse shifter vs TTD (delay)

Hi,

random waveforms: A mixture of sinusoiodal signals with different amplitude, frequency (and phase) (...according fourier)
I think "audio" is one of the best examples.

Klaus

 

[FvM]

Re: Phse shifter vs TTD (delay)

You would want to further elaborate "some radar application". Frequency? Bandwidth?

 

[ferdem]

Re: Phse shifter vs TTD (delay)

They can't be the same because a constant time delay(TTD) over a band can not provide a constant phase shift over that band. Phase shifters do provide constant phase shift over a band.
Can you say that 100 ps of time delay over the band of 2-4 GHz give the same phase shift over the same band?(No)

A time delay can be considered as phase shift(or vice versa) for a single frequency only.

 

[BradtheRad]

Re: Phse shifter vs TTD (delay)

A capacitor can delay a sinewave if you make an RC integrator (that is, a low-pass filter with capacitor connected across signal wires). If you repeat the process through several stages of filter, the phase shift is obvious. Eventually you can achieve a delay of several cycles.

What if we send a sinewave through a capacitor (that is, series capacitor, or differentiator or high-pass filter)? It performs an uncanny kind of phase shift. It advances the signal. By repeating the process through several stages, the phase shift can be made to appear to advance several cycles prior to the signal. Our sensible brain might want to call it an optical illusion, nevertheless the traditional engineering term we use for this effect is phase lead or phase advance.

Inductors can achieve a similar effect, by placing them in the right kind of filter.

- - - Updated - - -

Simulation of 6 stages of RC networks (capacitors in series).

Notice that even before completion of the first applied sine cycle, the later stages already display the phase advance.



Frequency and RC time constants were adjusted to combine so that each stage creates 60 degrees of advance. Thus 6 stages create one sine cycle of advance.

 

[pancho_hideboo]

Re: Phse shifter vs TTD (delay)

I am currently working on a TTD component for some radar application;
but I'm a bit confused about the difference between a phase shifter and delay component.
Ain't they should be same since phase difference is also a time delay in essence.

Assume modulated RF signal such as ASK.

Simple Delay means a delay regarding envelope.

Phase shift means a delay regarding RF carrier not envelope.

 

[ktr]

Re: Phse shifter vs TTD (delay)

I am trying to build a TTD component in X band with %20-30 BW. I searched through the literature; and found some ways to implement this. One of the methods was SPNT, maybe I can use SP4T for me to give TTD a 4-bit adjust. I thought of bending and making longer Transmission Lines to create a delay component; however TLIN have frequency dependency. that is confusing me.

What if we send a sinewave through a capacitor (that is, series capacitor, or differentiator or high-pass filter)? It performs an uncanny kind of phase shift. It advances the signal. By repeating the process through several stages, the phase shift can be made to appear to advance several cycles prior to the signal. Our sensible brain might want to call it an optical illusion, nevertheless the traditional engineering term we use for this effect is phase lead or phase advance.

I saw that too when making a phase shifter, they use allpass/allpass filters to make a UWB phase shifter, that is a really nice method.

 

[pancho_hideboo]

Re: Phse shifter vs TTD (delay)

however TLIN have frequency dependency.
that is confusing me.

Phase shift of TLIN is a linear phase shift regarding frequency, theta=-omega*Tdelay.

A linear phase shift regarding frequency results in a constant time delay regarding envelope.

I saw that too when making a phase shifter,
they use allpass/allpass filters to make a UWB phase shifter,

It is a synthesis of phase characteristics over frequency.

Delay equalizer is realized by overlapping of Allpass filters.

that is a really nice method.

Not so easy to realize.

 

[FvM]

Re: Phse shifter vs TTD (delay)

however TLIN have frequency dependency

Not sure what you mean. Transmission line has basically frequency independent delay.


Expect SP4T or SPNT to produce errors due to introducing unterminated or mismatched line segments. Better use fully terminated switch topology.

 

[vfone]

Re: Phse shifter vs TTD (delay)

The relation between Time Delay, Phase Shift, and Frequency is given by:

Time Delay (seconds) = [Phase Shift (°)] / [360 x Frequency (Hz)]