Page 180 - Build Your Own Transistor Radios a Hobbyists Guide to High-Performance and Low-Powered Radio Circuits

o Degree Signal Output

( I Signal Output )
Input Signal
Phase Shifter Circuit

90 Degrees Signal Output

( Q Signal Output)
FIGURE 12-4 A phasing system with a single input terminal and two

outputs for I and Q signals.
1. The I and Q outputs must maintain constant amplitude relative to each other.
2. The I and Q outputs must maintain a constant 90-degree difference in phase.
Any amplitude variation or deviation from the 90-degree phase difference between
the I and Q outputs over the frequency range will cause the image-reject mixer in

the computer to not completely reject the image signal.
Figure 12-5 provides an example phasing circuit that generates 0- and 90-degree
output.

R R R R lKl% R R lKl%

lKl% lKl% lKl% ~ lKl% ~
USA
~ C2A U2A CSA ,,.J I Signal 0
UlA
ClA , I •
" ./ v o Degree Ou
"
" R2A . v RSA • . v
R1A ., +v -
UOAP ~ L- .vn ,~
. vn ,;,;
~>_L . vn ~ J'~ ~ J '"'
'1 ~ J '"'
C = " +v J ,~
.!1 J'~
J '"'
RO R R R R R R lKl %
""
_J vn lK , ,, lKl% lK 1% lKl% lK , % 8 ~ U38
. ,
Ul8 C28 I f'I.... U28 C3B • I . , Q Signal 0
.
C18 , •
•
YI " ~ ~ 90 Degrees 0
"
'" R3B
Input Signal R18 R28 i +VI2 i + VI2
r"VI2
. . . . .
FIGURE 12-5 An analog phase-shifting circuit that prOVides I and Q
signals.
Before I explain operation of this phasing circuit, I would like to recommend a
terrific book on synthesizing filters and phase-shift networks by Arthur B. Williams.

It is called the Electronic Filter Design Handbook and is published by McGraw-Hill.
Any edition (e.g., the 1980 First Edition, 1989 Second Edition, 1995 Third Edition,
or the 2006 Fourth Edition) of this book will be helpful. And it is from this book that