Miscellaneous active electrical nonlinear devices – circuits – and – Specific input to output function – Combining of plural signals
Reexamination Certificate
1998-04-28
2001-02-20
Wells, Kenneth B. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific input to output function
Combining of plural signals
C327S356000
Reexamination Certificate
active
06191638
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a mixer circuit, and more particularly to an analogue mixer circuit which combines an intermediate frequency signal (hereinafter, called “IF signal”) with a local signal (hereinafter, called “LO signal”).
2. Description of the Related Art
FIG. 5
shows one example of the composition of a conventional mixer circuit
189
. With reference to
FIG. 5
, the mixer IC (integrated circuit)
188
comprises one npn-type transistor
145
. The collector of this transistor
145
is connected to an RE terminal
152
, the base is connected to an input terminal
149
, and the emitter is connected to a GND terminal
150
. The base of the npn-type transistor
145
is connected to the junction point between a resistor
146
and a resistor
147
. The other terminal of resistor
146
is connected to the collector of the npn-type transistor
145
. The other terminal of resistor
147
is connected to the earth terminal (hereinafter, called “GND terminal”)
150
of the mixer IC
188
. The collector of the npn-type transistor
145
is connected to a power supply terminal
151
and furthermore, a resistor
148
is connected between the collector of the npn-type transistor
145
and the power supply terminal
151
.
The power supply terminal
151
for supplying power to the mixer IC
188
is connected to a power supply
155
, and the RF terminal
152
is connected via a capacitor
154
to an RF output terminal
164
. Meanwhile, the input terminal
149
is connected via a capacitor
153
to the junction point between an inductor
157
and one terminal of a capacitor
160
. The other terminal of the inductor
157
is connected to the junction point between an inductor
156
and one terminal of a capacitor
158
. The other terminal of the inductor
156
is connected to an IF signal input terminal
162
, and the other terminal of the capacitor
158
is earthed.
The other terminal of the capacitor
160
is connected to the junction point between the capacitor
159
and one terminal of the inductor
161
, the other terminal of the capacitor
159
is connected to an LO signal input terminal
163
, and the other terminal of the inductor
161
is earthed.
A first band-eliminating filter (BEF
1
)
186
is constituted by the capacitor
159
, capacitor
160
and inductor
161
, and a second band-eliminating filter (BEF
2
)
187
is constituted by the inductor
156
, inductor
157
and capacitor
158
.
A mixer circuit
189
is formed by the foregoing composition. In this mixer circuit
189
, an IF signal is input from the IF signal input terminal
162
and it passes through the second band-eliminating filter
187
. Furthermore, an LO signal is input from the LO signal input terminal
163
, passes through the first band-eliminating filter
186
and is mixed with the IF signal as an input to the capacitor
153
.
The first band-eliminating filter
186
and the second band-eliminating filter
187
are provided in order to isolate the IF signal and LO signal. Consequently, for the IF signal, the LO side appears to be in an open state due to the first band-eliminating filter
186
, whilst for the LO signal, the IF side appears to be in an open state due to the second band-eliminating filter
187
. By this means, the IF signal and LO signal are added together without one signal leaking in the circuitry of the other, and they pass through the capacitor
153
and are input to the input terminal
149
of the mixer IC
188
.
The combined signal is amplified nonlinearly by the npn-type transistor
145
and it is then output from the RF terminal of the mixer IC
188
, passed through the capacitor
154
and output from the RF output terminal
164
.
Next, a further example of the related art is described with reference to FIG.
6
. The composition of the mixer circuit
190
is disclosed in Japanese Unexamined Patent 63-258107. With reference to
FIG. 6
, in the mixer circuit
190
, the collector of a transistor
165
is earthed via a capacitor
170
. Therefore, this is similar to the high-frequency region being earthed. Furthermore, the npn-type transistor
165
operates nonlinearly, but the inductor
176
is connected via a capacitor
171
to the base of the npn-type transistor
165
. The input terminal
180
of a local oscillator input from an external source is connected to the base of the npn-type transistor
165
via a wave filter circuit
177
and a capacitor
172
. A capacitor
169
and a capacitor
173
are provided respectively between the base and emitter terminals, and between the emitter and GND terminals, of the npn-type transistor
165
. The terminal
182
is a modulation signal input terminal. In addition, the emitter of the npn-type transistor
165
is connected to an output terminal
181
via a wave filter circuit
178
.
By means of the foregoing composition, the emitter of the transistor
165
outputs a signal wherein a signal of frequency components input from the local oscillator and a signal of frequency components oscillating in the inductor
176
and capacitor
169
, and capacitor
173
, are combined with each other. Thereupon, the required signal only is extracted from a number of combined frequency component signals by means of the wave filter circuit (filter)
178
.
FIG. 7
shows the results of a simulation of a conventional mixer circuit. In
FIG. 7
, the input frequency, f
IF
, of the IF signal is set to a constant 150 (MHz) at IF signal input power of P
IFin
=−35 (dBm). The output power P
RF
, of the RF signal when the input power of the LO signal, P
LO
, is swept is indicated by the symbol □, and the signal leakage from the LO terminal to the IF terminal is indicated by the symbol &ogr;, and the signal leakage from the IF terminal to the LO terminal is indicated by the symbol ∇, these values being plotted on a graph. In the graph, the LO signal frequency, f
LO
is 800 (MHz), and the RF signal frequency, f
RF
, is 950 MHz.
However, there have been the following problems with conventional mixer circuits.
The conventional mixer circuit
89
shown in
FIG. 5
is composed such that the IF signal and LO signal are input via the same input terminal
149
of the mixer IC
188
. Therefore, in order to isolate the IF signal and LO signal, it has been necessary to insert a first band-eliminating filter
186
and a second band-eliminating filter
187
comprising inductors and capacitors in the respective signal paths. Accordingly, there has been a problem in that this increases the installation surface area of the chip components forming the mixer circuit
18
.
Moreover, in the mixer circuit
190
illustrated in
FIG. 6
, a large number of additional components, such as a bypass capacitor (capacitor
170
), inductor
176
, and a variable-voltage capacitor (varactor)
175
, etc. are required, andthis requires aneven larger installation surface area. A further problem arises in that since the collector of the npn-type transistor
165
is earthed, insufficient conversion gain is obtained from the mixer circuit
190
.
SUMMARY OF THE INVENTION
Therefore, the present invention was devised with the foregoing in view, an object thereof being to provide a mixer circuit whereby band-eliminating filters become unnecessary and size reductions can be achieved, whilst obtaining prescribed mixing characteristics.
In order to achieve this object, the mixer circuit according to the present invention comprises a first transistor and a second transistor of opposite conduction types, which are mutually connected, wherein the emitter of the first transistor is connected to the collector of the second transistor. It also comprises: a third transistor whose collector is connected to the emitter of the first transistor; a power supply terminal connected to the collector of the first transistor; an RF terminal connected to the collector of the first transistor; an LO terminal connected to the base of the first transistor; an IF terminal connected to the base of the second transistor; and a ground terminal connected to the emit
McGinn & Gibb PLLC
NEC Corporation
Wells Kenneth B.
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