Miscellaneous active electrical nonlinear devices – circuits – and – Specific input to output function – Combining of plural signals
Reexamination Certificate
1997-01-27
2002-10-29
Callahan, Timothy P. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific input to output function
Combining of plural signals
C327S113000, C327S551000, C455S326000
Reexamination Certificate
active
06472925
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a mixer circuit for mixing a plurality of input signals with each other, and more particularly, it relates to a mixer circuit having a high conversion gain, which is improved in linearity.
2. Description of the Background Art
FIG. 16
is a circuit diagram showing the structure of a conventional Gilbert cell type mixer circuit. Referring to
FIG. 16
, reference character
1
G denotes a differential amplifier for amplifying an input voltage v
1
, and reference character
4
A denotes a mixer part for mixing an output of the differential amplifier
1
G with an input voltage v
2
. The conventional mixer circuit is formed by the mixer part
4
A and the differential amplifier
1
G, for outputting first and second output currents i
1
and i
2
from first and second output terminals
19
and
20
respectively.
The differential amplifier
1
G is formed by an NPN bipolar transistor Q
27
having a base which is connected to a non-inverting input terminal
150
and a collector which is connected to a first non-inverting input terminal
17
of the mixer part
4
A and an emitter, an NPN bipolar transistor Q
28
having a base which is connected to an inverting input terminal
151
and a collector which is connected to a first inverting input terminal
18
of the mixer part
4
A and an emitter, current sources
152
and
153
for extracting prescribed direct currents IEE from a node which connects the emitters of the transistor Q
27
and a resistor
154
and from a node which connects the emitter of the transistor Q
28
and resistor
154
respectively, and the resistor
154
connecting the emitters of the transistors Q
27
and Q
28
with each other.
The mixer part
4
A is formed by an NPN bipolar transistor Q
3
having a base, a collector and an emitter which are connected to a second non-inverting input terminal
15
, the first output terminal
19
and the first non-inverting input terminal
17
respectively, an NPN bipolar transistor Q
4
having a base, a collector and an emitter which are connected to a second inverting input terminal
16
, the second output terminal
20
and the first non-inverting input terminal
17
respectively, an NPN bipolar transistor Q
5
having a base, a collector and an emitter which are connected to the second inverting input terminal
16
, the first output terminal
19
and the first inverting input terminal
18
respectively, and an NPN bipolar transistor Q
6
having a base, a collector and an emitter which are connected to the second non-inverting input terminal
15
, the second output terminal
20
and the first inverting input terminal
18
respectively.
The inputted first input voltage v
1
is amplified by an emitter differential pair circuit which is formed by the transistors Q
27
and Q
28
, and appears as a difference between respective collector currents of the transistors Q
27
and Q
28
. The respective collector currents of the transistors Q
27
and Q
28
define tail currents of an emitter differential pair circuit which is formed by the transistors Q
3
and Q
4
and that formed by the transistors Q
5
and Q
6
. The second input voltage v
2
is amplified by these emitter differential pair circuits formed by the transistors Q
3
, Q
4
, Q
5
and Q
6
.
The aforementioned relations are expressed in the following numerical formulas. Ignoring the resistance value of the resistor
154
, the respective collector currents ic
27
and ic
28
of the transistors Q
27
and Q
28
are expressed in the following numerical formulas 1 and 2:
ic27
=
2
IEE
1
+
exp
[
-
v1
V
T
]
(
1
)
ic28
=
2
IEE
1
+
exp
[
-
v1
V
T
]
(
2
)
Assuming that ic
3
, ic
4
, ic
5
and ic
6
represent respective collector currents of the transistors Q
3
to Q
6
, these collector currents ic
3
to ic
6
are expressed in the following numerical formulas 3 to 6:
ic3
=
ic27
1
+
exp
[
-
v2
V
T
]
(
3
)
ic4
=
ic27
1
+
exp
[
v2
V
T
]
(
4
)
ic5
=
ic28
1
+
exp
[
v2
V
T
]
(
5
)
ic6
=
ic28
1
+
exp
[
-
v2
V
T
]
(
6
)
From the numerical formulas 1 to 6, the collector currents ic
3
to ic
6
of the transistors Q
3
to Q
6
and the first and second input voltages v
1
and v
2
have relations of the following numerical formulas 7 to 10:
ic3
=
2
IEE
[
1
+
exp
[
-
v1
V
T
]
]
[
1
+
exp
[
-
v2
V
T
]
]
(
7
)
ic4
=
2
IEE
[
1
+
exp
[
-
v1
V
T
]
]
[
1
+
exp
[
v2
V
T
]
]
(
8
)
ic5
=
2
IEE
[
1
+
exp
[
v1
V
T
]
]
[
1
+
exp
[
v2
V
T
]
]
(
9
)
ic6
=
2
IEE
[
1
+
exp
[
v1
V
T
]
]
[
1
+
exp
[
-
v2
V
T
]
]
(
10
)
From the numerical formulas 7 to 10, a differential output current (i
1
−i
2
) is given by the following numerical formula 11:
i1
-
i2
=
ic3
+
ic5
-
(
ic6
+
ic4
)
=
2
IEE
[
tanh
[
v1
2
V
T
]
]
[
tanh
[
v2
2
V
T
]
]
(
11
)
In general, tanhx can be expanded in a series as follows:
tanh
x
=
x
-
x
3
3
(
12
)
If x is sufficiently less than 1 in the numerical formula 11, the numerical formula 12 can be transformed into the following numerical formula 13, and hence the relation between the input voltages v
1
and v
2
and the output signals i
1
and i
2
is expressed in the following numerical formula 14:
tanh
x
≈
x
(
13
)
i1
-
i2
≈
2
IEE
[
v1
2
V
T
]
[
v2
2
V
T
]
(
14
)
Namely, this mixer circuit is adapted to multiply the first input voltage v
1
by the second input voltage v
2
. If the first and second input voltages v
1
and v
2
are two signals having different frequencies f
1
and f
2
, the mixer circuit multiplies these two signals by each other, thereby outputting signals having frequency components of the sum |f
1
+f
2
| of and the difference |f
1
−f
2
| between the frequencies of the two signals.
The emitters of the transistors Q
27
and Q
28
are connected with each other through the resistor
154
, whereby a negative feedback effect results in the emitter differential pair circuit which is formed by the transistors Q
27
and Q
28
. Namely, the conversion gain Gc of the mixer circuit is in inverse proportion to the resistance value of the resistor
154
forming a negative feedback circuit. The following numerical formula
15
expresses the relation between the conversion gain Gc and the resistance value RE of the resistor
154
:
G
c
∝
1
RE
(
15
)
In order to increase the gain of the conventional mixer circuit having the aforementioned structure, the resistance value RE of the resistor
154
must be reduced. If the resistance value RE of the resistor
154
is reduced, however, nonlinearity of the circuit is disadvantageously increased to cause excess harmonics or intermodulation distortion.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention, a mixer circuit comprises a mixer part having first and second input terminals and an output terminal for mixing first and second signals which are inputted from the first and second input terminals with each other, and an amplifier having an input terminal for receiving a third signal, an output terminal which is connected to the first input terminal, and a negative feedback circuit having a prescribed pass characteristic for passing the third signal with no filtration for feeding back an output signal, for amplifying the third signal and outputting the same to the mixer part as the first signal.
According to a second aspect of the present invention, the prescribed pass characteristic of the negative feedback circuit is a low-pass characteristic.
According to a third aspect of the present invention, the first input terminal of the mixer part comprises a first inverting input terminal and a first non-inverting input terminal, the second input terminal comprises a second inverting input terminal and a second non-inverting input terminal, the input terminal of the amplifier comprises an inverting input terminal for inputting the third sig
Komurasaki Hiroshi
Satoh Hisayasu
Burns Doane , Swecker, Mathis LLP
Callahan Timothy P.
Englund Terry L.
Mitsubishi Denki & Kabushiki Kaisha
LandOfFree
Mixer circuit with negative feedback filtering does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Mixer circuit with negative feedback filtering, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Mixer circuit with negative feedback filtering will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2976471