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# Basic Communication Question

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Hello everybody

How can I practically extract the I and Q components from a signal?

Why I would better send I and Q rather than the overall signal at a time?

#### safwatonline

Hello everybody

How can I practically extract the I and Q components from a signal?

Why I would better send I and Q rather than the overall signal at a time?

hello,
here is what i know>> simply multiply by the carrier to get I and by the carrier shifted by π/2 to get Q, then use parallel to series converter to add them."note u have to extract the carrier using CDR"
i guess if u send the overall signal at the a time u will need larger "double" BW for the same rate. (u can think in it as if u send double the information with the same BW, one symbol=2bits".
but i think there r some disadvantages like complexty and if u increase the number of bits per symbol further u will suffer from increase in BER "note as far as i can remember using 2 bits/symbol dont increase BER".
i hope this help "note ana fatet keteeeeeer "
salam

Points: 2

#### jlee

##### Member level 2
I and Q components can be extracted by using two mixers (We call them I-Q mixer):

1. The first mixer is mixing down the signal with LO signal, 0 degree phase;
2. The second mixer is mixing down the signal with LO signal, 90 degree phase;
I component is the addition of two mixers' output, Q component is the subtraction of two mixers' ouput.

The complexity is that now you need two mixers (more area, more power). And the two LO signals (0 phase and 90 degree phase) should be accurate... phase error and amplitude error will cause inaccurate results. The details on how much each error affect the result can be found in Razavi's RF book, or Tom Lee's book.

Points: 2

#### jcpu

##### Full Member level 4
Mathmatically,
I==>in phase component,
in common language,
this is just like in Fourier analysis,
one single frequency signal can have two components:
namely, cosine and sine.
These two components are independent (or orthogonal),
that is they can carry different baseband signal independently.

when we talk about overall signal in
Why I would better send I and Q rather than the overall signal at a time?
it is believed to mean passband signal
that is signal with carrier.

Those baseband signal can always be recovered by removing carrier,
in RF stage, low IF stage, or DSP stage,....as described upstairs.

Text book like "communication circuits" by Carlson is very good in
explaining all these.

Points: 2

First, thank you all who replied,

Also, does anyone has Carlson book as e-book?

Thank you all,