Need Help About Multibit Phase Shifter

[monolothics]

Hi,,

I want to design a 4-bit High/Low Pass Phase Shifter with lumped element (L-C)

for all i know 4-bit phase shifter i will produce 16 difference phase shift that is : 0, 22.5, 45, 67.5, 90, 112.5, 135, ... , 337.5 (degree)
and also the 4-bit phase shifter consist of 4 phase bit = 180, 90, 45 and 22.5 (degree), and each phase bit will have 2 phase state
and usually the phase state is consist of phase 0 (degree) as phase reference usually at high pass branch and other value of phase in low pass branch
to create phase difference : ΔΦ = Φ high pass - Φ low pass ; the phase difference is represent the phase bit.

So the problems are : when i'm using 0 degree as my phase reference i couldn't find an appropriate value for my lumped elements but i can satisfy the value of 16 difference phase shift. But if i change the phase reference into any value i can get the value of the lumped elements but i couldn't get the value of 16 difference phase shift.

so anyone has an ideas how to solve this problem...

thank you

 

[vfone]

I don't know what configuration and how many poles you use for the phase shifting reactive components, but have to know that a single pole RC or RL can give a maximum 90-deg phase shift. For 180-deg you need at least two poles, or one L and one C. In real life designers use a Pi network C-L-C to get a certified maximum 180-deg phase shift.

 

[zorro]

So the problems are : when i'm using 0 degree as my phase reference i couldn't find an appropriate value for my lumped elements but i can satisfy the value of 16 difference phase shift. But if i change the phase reference into any value i can get the value of the lumped elements but i couldn't get the value of 16 difference phase shift.
so anyone has an ideas how to solve this problem...

Hi Monolothics,

I don't understand. Can you clarify where is the problem, maybe giving an example?
Regards

Z

 

[monolothics]

Hi Monolothics,

I don't understand. Can you clarify where is the problem, maybe giving an example?
Regards

Z

maybe this can explain what i want to asked :




from that picture
usually the reference is 0 and delay line is the value of phase bit itself
for example :
90 phase shift can be achieved by 0 at the reference and 90 at delay line

but 0 phase shift is hard to achieve especially using HPF/LPF phase shifter type

so from information that i get,
we can use -45° and 45° to achieve 90° phase shift ; or -90° and 90° to achieve 180 phase shift ; or -25° and 20° to achieve 45° phase shift

but what confuse me is, when those 180 , 90 and 45 phase shift is cascaded into 3-bit phase shifter i can't achieve phase increment of 3-bit phase shifter according this table :



so this is my problem
i hope you can understand it..

 

[zorro]

Hi Monolothics,

If your 3-bit word is composed by b2,b1,b0 (b2 is the MSB and b0 the LSB), then:

b0 switches +/-22.5° (b0=0 inserts -22.5°; b0=1 inserts +22.5°)
b1 switches +/-45° (b1=0 inserts -45°; b1=1 inserts +45°)
b2 switches +/-90° (b2=0 inserts -90°; b2=1 inserts +90°)

Of course, there is a constant 157.5° phase shift, but what cares is the phase increments between states, so it is no problem.
If this constant phase shift your concern?
Regards

Z

 

[monolothics]

Of course, there is a constant 157.5° phase shift, but what cares is the phase increments between states, so it is no problem.
If this constant phase shift your concern?

Hi, zorro thanks for the reply.

Yes that exactly what concern me.

So, it's no problem if i have 157.5° phase shift in 3-bit phase shifter?? but can you explain it why it's not a problem??

thanks

 

[zorro]

It's like a piece of cable. You will always have a constant shift in the connections (inside or outside the shifter).
Phase variations is what matters.
For example, when used in a phased array, a constant phase common to all the channels has no effect. It is the phase difference between elements of the array what makes beam steering.
Regards

Z

 

[monolothics]

It's like a piece of cable. You will always have a constant shift in the connections (inside or outside the shifter).
Phase variations is what matters.
For example, when used in a phased array, a constant phase common to all the channels has no effect. It is the phase difference between elements of the array what makes beam steering.
Regards

Z

okay,,i understand now
thanks for your answer zorro
it's really helpful