Telecommunications – Receiver or analog modulated signal frequency converter – Frequency modifying or conversion
Reexamination Certificate
1999-02-19
2001-08-14
Maung, Nay (Department: 2681)
Telecommunications
Receiver or analog modulated signal frequency converter
Frequency modifying or conversion
C455S333000, C327S359000
Reexamination Certificate
active
06275688
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to a double balanced mixer, and, more particularly, to a double balanced mixer used in mobile communication device such as portable telephones.
FIG. 1
is a schematic block diagram of a conventional mobile communication device
10
, such as a portable telephone, that can perform analog and digital communications.
The communication device
10
is equipped with a mixer circuit
11
for digital communications and an amp circuit
12
for analog communications. The communication device
10
is also equipped with switches
14
and
15
for switching between the mixer circuit
11
and the amp circuit
12
in order to allow sharing of elements, such as antennas, between the analog and digital communications.
In digital communications, a control circuit
13
operates the switches
14
and
15
to active the mixer circuit
11
. In this case, an oscillation signal output from an oscillation circuit
16
is input to the mixer circuit
11
as a carrier signal LO via the switch
14
. The mixer circuit
11
generates an output signal RFout by mixing the carrier signal LO and a base band signal IF having an intermediate frequency. The output signal RFout is supplied to a subsequent circuit (not shown) via the switch
15
.
In analog communications, the control circuit
13
operates the switches
14
and
15
to active the amp circuit
12
. In this case, the oscillation signal output from the oscillation circuit
16
is input to the amp circuit
12
via the switch
14
as an input signal RFin. The amp circuit
12
generates the output signal RFout by amplifying the input signal RFin. The output signal RFout is supplied to the subsequent circuit via the switch
15
.
The circuit area of the communication device
10
is increased by including both of the amp circuit
12
and the mixer circuit
11
. Further, because the communication device
10
also requires the switches
14
and
15
, its circuit area is further increased.
To make the communication device
10
compact, it would be advantageous to also use the mixer circuit
11
as an amp circuit in analog communications.
FIG. 2
is a schematic circuit diagram of the mixer circuit
11
. The mixer circuit
11
is a double balanced mixer (DBM). The mixer circuit
11
includes transistors Tr
1
to Tr
6
, resistors R
1
to R
3
, and constant-current sources
21
and
22
. The first and second transistors Tr
1
and Tr
2
form a first differential amplifier
23
in which both emitters are connected to each other. The collectors of the first and second transistors Tr
1
and Tr
2
are connected to a high potential power supply Vcc via the resistors R
1
and R
2
.
The third and fourth transistors Tr
3
and Tr
4
form a second differential amplifier
24
in which both emitters are connected to each other. The collectors of the third and fourth transistors Tr
3
and Tr
4
are connected to the high potential power supply Vcc via the resistors R
1
and R
2
.
The fifth and sixth transistors Tr
5
and Tr
6
form a third differential amplifier
25
in which both emitters are connected to each other via the resistor R
3
. The emitters of the fifth and sixth transistors Tr
5
and Tr
6
are connected to low potential power supplies (grounds GND) via the constant-current sources
21
and
22
.
The collector of the fifth transistor Tr
5
is connected to the emitters of the first and second transistors Tr
1
and Tr
2
. The collector of the sixth transistor Tr
6
is connected to the emitters of the third and fourth transistors Tr
3
and Tr
4
.
As the mixer circuit, the base band signal IF is applied to the bases of the first to fourth transistors Tr
1
to Tr
4
, and the carrier signal LO is applied to the bases of the fifth and sixth transistors Tr
5
and Tr
6
. Then, the output signal RFout is output from the collectors of the first and third transistors Tr
1
and Tr
3
and the collectors of the second and fourth transistors Tr
2
and Tr
4
.
As the amp circuit, a first control signal S
1
is applied to the bases of the first and fourth transistors Tr
1
and Tr
4
and a second control signal S
2
is applied to the bases of the second and third transistors Tr
2
and Tr
3
. In this case, the first and second control signals S
1
and S
2
are set so that the first and second differential amplifiers
23
and
24
will be unbalanced.
For example, the first control signal S
1
having an H level is applied to the bases of the first and fourth transistors Tr
1
and Tr
4
and the second control signal S
2
having an L level is applied to the bases of the second and third transistors Tr
2
and Tr
3
. Hence, the first and fourth transistors Tr
1
and Tr
4
turn on and the second and third transistors Tr
2
and Tr
3
turn off. Thus, the mixer circuit
11
operates as a differential amplifier by using the third differential amplifier
25
. In other words, the fifth and sixth transistors Tr
5
and Tr
6
amplify the input signal RFin applied to the bases, and the output signal RFout is output from the collectors of the first and fourth transistors Tr
1
and Tr
4
.
When the mixer circuit
11
operates as an amp, the two constant-current sources
21
and
22
are operating. However, the third differential amplifier
25
can be operated only by either the constant-current source
21
or
22
. Accordingly, during amp operation, unnecessary current flows in the mixer circuit
11
. Consequently, the power consumption of the circuit is greater than necessary.
It is an object of the present invention to provide a double balanced mixer having a small size and low power consumption.
SUMMARY OF THE INVENTION
Briefly stated, the present invention provides a double balanced mixer includes a first differential amplifier including a first pair of transistors having their emitters connected to each other, a second differential amplifier including a second pair of transistors having their emitters connected to each other, and a third differential amplifier, connected to the first and second differential amplifiers, including a third pair of transistors having their emitters connected to each other via a resistor. First and second constant-current sources are connected to the emitters of the third pair of transistors, respectively. A gate circuit is connected to one of the first and second constant-current sources and selectively activates the connected one of first and second constant-current sources in response to a control signal.
The present invention provides an orthogonal modulator includes a frequency multiplier for receiving a carrier signal and generating a multiplied signal in which the frequency of the carrier signal is multiplied by a predetermined factor. A phase shifter is connected to the frequency multiplier, receives the multiplied signal and generates a first carrier signal which is an in-phase component of the carrier signal, and a second carrier signal which is an orthogonal component of the carrier signal, by dividing the multiplied signal. A first mixer is connected to the phase shifter, receives the first carrier signal and a first base band signal and generates a first modulation signal by mixing the first carrier signal and the first base band signal. A second mixer is connected to the phase shifter, receives the second carrier signal and a second base band signal and generates a second modulation signal by mixing the second carrier signal and the second base band signal. An adder is connected to the first and second mixers, receives the first and second modulation signals and generates an output signal by adding the first and second modulation signals. The first mixer includes a first differential amplifier including a first pair of transistors having their emitters connected to each other and their bases receiving the first carrier signal, a second differential amplifier including a second pair of transistors having their emitters connected to each other and their bases receiving the first carrier signal, and a third differential amplifier, connected to the first and second differential amplifiers, including
Takagi Minoru
Tsukahara Masahiro
Armstrong Westerman Hattori McLeland & Naughton LLP
Fujitsu Limited
Gelin Jean A
Maung Nay
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