Telecommunications – Transmitter – Frequency conversion
Reexamination Certificate
1999-10-28
2003-07-29
Le, Thanh Cong (Department: 2684)
Telecommunications
Transmitter
Frequency conversion
C455S112000, C455S318000, C327S355000
Reexamination Certificate
active
06600906
ABSTRACT:
FIELD OF THE INVENTION
The present invention pertains to a frequency up/down converter.
BACKGROUND OF THE INVENTION
Frequency up/down converters (referred to below as up/down converters) are known as a technology for frequency conversion.
FIG. 1
shows a diagram of a conventional up converter and
FIG. 2
shows a diagram of a conventional down converter.
First, a conventional up converter will be described while referring to FIG.
1
. First local oscillator LO
1
124
of the up converter in
FIG. 1
is typically a low phase-noise signal source of a fixed frequency and second local oscillator LO
2
126
is a low phase-noise signal source of a variable frequency. In
FIG. 1
, signals given to input terminal
110
are passed through BPF (band pass filter)
112
and mixed with signals from LO
1
124
(of a predetermined fixed frequency) by mixer
114
and the frequency component of the difference between the two signals is removed, that is, the frequency component of the sum of the two signals, is produced by BPF
116
. There is further mixing with signals output at a predetermined frequency from LO
2
126
by mixer
118
and the frequency component of the sum of the two signals is removed by LPF (low pass filter)
120
and output to output terminal
122
.
In this case, assuming that signal f
110
given to input terminal
110
is
f
110
=cos(
w
—
if*t
) (1)
as a signal without phase noise, signal f
124
output from LO
1
is
f
124
=cos(
w
2
*
t+&thgr;pn
2
(
t
)) (2)
with phase noise as &thgr;pn
2
(t), and signal f
126
from LO
2
is
f
126
=cos(
w
3
*
t+&thgr;pn
3
(
t
)) (3)
with phase noise as &thgr;pn
3
(t), first intermediate frequency signal IF
1
at the output of mixer
114
is the product of both signals f
110
and f
124
. To summarize,
IF1
=
cos
(
w_if
*
t
)
*
cos
(
w2
*
t
+
θ
pn2
(
t
)
)
=
(
cos
(
(
w_if
+
w2
)
*
t
+
θ
pn2
(
t
)
)
+
cos
(
(
w_if
-
w2
)
*
t
-
θ
pn2
(
t
)
)
)
/
2
(
4
)
Furthermore, in this specification, the formulas representing signals that have passed through mixers or filters focus on the relationship with frequency for what needs explanation, but persons skilled in the art can alter the formulas as needed for amplitude, and therefore, the details are not given special mention. Therefore, the phrase “to summarize” has been used when the formulas are introduced.
Next, the lower frequency components are removed by BPF
116
, and therefore, signal f
116
at the output of BPF
116
becomes
f
116
=cos((
w
—
if+w
2
)*
t+&thgr;pn
2
(
t
)) (5)
When frequency is converted by mixer
118
, second intermediate frequency signal IF
2
at the output of mixer
118
becomes
IF2
=
cos
(
w3
*
t
+
θ
pn3
(
t
)
)
*
cos
(
(
w_if
+
w2
)
*
t
+
θ
pn2
(
t
)
)
=
(
cos
(
(
w3
+
w_if
+
w2
)
*
t
+
θ
pn3
(
t
)
+
θ
pn2
(
t
)
)
+
cos
(
(
w3
-
w_if
-
w2
)
*
t
+
θ
pn3
(
t
)
-
θ
pn
(
t
)
)
)
/
2
(
6
)
The higher frequency components are removed by LPF
120
here, and therefore, signal f
120
at the output of LPF
120
becomes
f
120
=cos((
w
3
−w
—
if−w
2
)*
t+&thgr;pn
3
(
t
)−&thgr;
pn
2
(
t
)) (7)
In formula (7), since &thgr;pn
3
(t) and &thgr;pn
2
(t) are non-correlated noise from different signal sources, these phase noises are added to the signal f
120
to output terminal
122
and given to output. The results relating to phase noise here would not be different, if the component of lower frequency from first intermediate frequency IF
1
was used.
Next, a conventional down converter will be described while referring to FIG.
2
. First local oscillator LO
1
226
of the down converter in
FIG. 2
is a low phase-noise signal source of variable frequency and second local oscillator LO
2
224
is a low phase-noise signal source of fixed frequency. The signal given to input terminal
222
passes through LPF
220
in
FIG. 2
in order to remove images of frequency components and is mixed with a signal of a predetermined frequency from first local oscillator LO
1
226
by mixer
218
. The frequency component of the sum of both signals is removed by BPF
216
, and further mixing with signals (of a predetermined fixed frequency) from second local oscillator LO
2
224
is performed by mixer
214
. The frequency component of the sum of the two signals is removed by BPF
212
and, then the result is output to output terminal
210
.
In this case, assuming that input signal f
222
of input terminal
222
is
f
222
=cos(
w
—
in*t
) (8)
as a signal without phase noise, signal f
226
from first local oscillator LO
1
is
f
226
=cos(
w
1
*
t+&thgr;pn
1
(
t
)) (9)
with phase noise as &thgr;pn
1
(t), and signal f
224
from second local oscillator LO
2
224
is
f
224
=cos(
w
2
*
t+&thgr;pn
2
(
t
)) (10)
with phase noise as &thgr;pn
2
(t), first intermediate frequency signal IF
1
at the output of mixer
218
becomes the product of input signal f
222
and signal f
226
from LO
1
and
IF1
=
cos
(
w1
*
t
+
θ
pn1
(
t
)
)
*
cos
(
w_in
*
t
)
=
(
cos
(
(
w1
+
w_in
)
*
t
+
θ
pn1
(
t
)
)
+
cos
(
(
w1
-
w_in
)
*
t
+
θ
pn1
(
t
)
)
)
/
2
(
11
)
Here, the higher component is removed by BPF
216
and therefore, signal f
216
at the output of BPF
216
becomes
f
216
=cos((
w
1
−
w
—
in
)*
t+&thgr;pn
1
(
t
)) (12)
Next, when frequency is converted by mixer
214
, second intermediate frequency signal IF
2
at the output of mixer
214
becomes
IF2
=
cos
(
(
w1
-
w_in
)
*
t
+
θ
pn1
(
t
)
)
*
cos
(
w2
*
t
+
θ
pn2
(
t
)
)
=
(
cos
(
(
w1
-
w_in
+
w2
)
*
t
+
θ
pn1
(
t
)
+
θ
pn2
(
t
)
)
+
cos
(
(
w1
-
w_in
-
w2
)
*
t
+
θ
pn1
(
t
)
-
θ
pn2
(
t
)
)
)
/
2
(
13
)
and when the higher component is dropped by BPF
212
, signal f
212
at the output of BPF
212
becomes
f
212
=cos((
w
1
−w
—
in−w
2
)*
t+&thgr;pn
1
(
t
)−&thgr;
pn
2
(
t
)) (14)
In formula (14), since &thgr;pn
3
(t) and &thgr;pn
2
(t) are non-correlated noise from different signal sources, these phase noises are added to output signals and are given to output.
Accordingly, there is a disadvantage with conventional up/down converters in that phase noise from internal signal sources is obtained in the output and it becomes necessary to use a high-performance internal signal source with low phase-noise in order to keep phase noise to lower.
In particular, signal sources
124
and
224
of fixed frequency in conventional up/down converters must have as high an output frequency as signal sources
126
and
226
of variable frequency. In general, as higher the output frequency becomes in a signal source, the phase noise level also increases. Therefore, a signal source with low phase-noise is needed, even when used as the signal source of fixed frequency, and as a result, the up/down converter becomes expensive.
Therefore, when this type of conventional converter is used in systems such as IC testers, etc., the cost of developing a dedicated fixed frequency signal source increases and becomes expensive. Moreover, output frequency cannot be varied, and therefore, this signal source cannot be flexibly used with other modules. Consequently, the problems with these conventional converters are two-fold.
Therefore, there was a need for a high-frequency up/down converter with which phase noise is reduced even if a l
Agilent Technologie,s Inc.
Cong Le Thanh
Trinh Tan
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