JP2006114965A - Frequency changer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a frequency changer reducing an unwanted spurious signal generated by the fact that a local oscillation signal to be inputted from a local oscillator to a signal selecting circuit mutually propagates into the other local oscillator. <P>SOLUTION: This frequency changer is provided with amplifiers each capable of switching a gain to allow only a desired frequency signal to pass by an external control signal, between a local oscillator 1 and a signal selecting circuit 3 and between a local oscillator 2 and the signal selecting circuit 3. The gain of each of the amplifiers is switched so that only the desired frequency signal to be selected by the external control signal may pass, thereby adjusting the input levels of two signals to be inputted into the signal selecting circuit 3, and the level of signals propagating with each other are suppressed, thereby suppressing the generation of the unwanted spurious. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a frequency converter used in a wireless communication device such as a mobile phone terminal having a plurality of frequency bands, and particularly to a frequency converter configured so that an unnecessary spurious component is not included in an output signal.

  In recent years, wireless communication devices such as mobile phone terminals tend to be miniaturized, and parts to be used are required to be reduced in number by integration. The frequency converter is also integrated with other circuits such as sharing the local oscillator with other circuits, especially in the signal processing section for transmission and reception, and large-scale integration has progressed, resulting in signal interference inside the IC. It has become a big problem.

  As a conventional frequency converter, the one shown in FIG. 2 is known. In FIG. 2, 1 is a first local oscillator, 2 is a second local oscillator, 3 is a signal selection circuit, 4 is a frequency converter, and 5 is another circuit block that shares the local oscillator signal of the local oscillator 2. . In the signal selection circuit 3, as shown in FIG. 3, the transistors 31, 33 (hereinafter Tr) share their collectors and the load R1 of 36, and Tr32, 34 have their collectors and the load R2 of 35, respectively. The bases of Tr 31 and 32 are the input a from the local oscillator 1, and the bases of Tr 33 and 34 are the input b from the local oscillator 2.

Next, the operation will be described. The local oscillation signal of frequency f1 output from the local oscillator 1 is input to the input a of the signal selection circuit 3, and the local oscillation signal of frequency f2 output from the local oscillator 2 is input b of the signal selection circuit 3. Is input. The signal selection circuit 3, when selecting the signal of the frequency f1 input to the input a, causes the current of the current source 37 to flow, prevents the current of the current source 38 from flowing, and includes Tr31 and 32. The differential amplifier circuit 39 is operated. When the signal of the frequency f2 input to the input b is selected, the current of the current source 38 is allowed to flow and the current of the current source 37 is not allowed to flow. A signal having a desired frequency is selected and input to the frequency conversion circuit 4. On the other hand, the local signal f2 output from the local oscillator 2 is also input to another circuit block 5 for use.
JP-A-11-68863

  However, according to this frequency converter configuration, the signal selection circuit 3 has a common collector and load 36 for Tr31 and Tr33, and a common collector and load 35 for Tr32 and Tr34. The local oscillation signal f2 circulates from the collector of Tr33, 34 to the collector of Tr31, 32 of the differential amplifier circuit 39 for selecting the local oscillation signal f1, and the local oscillation signal f1 is the collector of Tr31, 32. To the collector of the Tr33, 34 of the differential amplifier circuit 40 that selects the local oscillation signal f2, and the local oscillation signal of the frequency that is not selected is combined with the local oscillation signal of the frequency that is not selected Then, the signal passes through the frequency converter 4 and is converted into an unnecessary spurious signal in the output signal.

  For example, it is assumed that the local signal f1 of the input a is selected by the signal selection circuit 3. At this time, the local oscillator 2 is operating to send a local oscillation signal f2 to another circuit block 5, and the local oscillation signal f2 is also input to the input b of the signal selection circuit 3, and the collectors of the Tr33 and 34 are connected. Then, it goes around to the collectors of the transistors Tr31 and Tr32 and is input to the frequency conversion circuit 4 together with a desired local oscillation signal f1 by the differential amplifier circuit 39, and is output as an unnecessary spurious output signal. In addition, the local oscillation signal f1 also circulates to the collectors of the Tr33 and 34 via the collectors of the Tr31 and 32, and is input to another circuit block 5 via the input b and is unnecessary for the output signal of the other circuit block. May occur. Unnecessary spurious signals must be removed because they become disturbing waves of the desired wave.

  The present invention solves the above-described conventional problems, and an object thereof is to reduce unnecessary spurious included in an output signal.

  In order to achieve the above object, the frequency converter according to the present invention provides a desired frequency between the local oscillator 1 and the signal selection circuit 3 and between the local oscillator 2 and the signal selection circuit 3 by an external control signal. The amplifier has an amplifier capable of switching the gain so that only a signal of a frequency can pass. By switching the gain of the amplifier so that only a signal of a desired frequency selected by the external control signal passes, isolation between the two signals input to the signal selection circuit 3 is performed. It is possible to reduce the spurious generated from the leakage.

  According to the frequency converter according to the present invention, two local oscillation signals cause interference at the output part of the circuit due to insufficient isolation of the signal selection circuit, preventing unnecessary components from being injected into the frequency converter, Unnecessary spurious components mixed in the output signal can be greatly reduced.

(First embodiment)
Hereinafter, the configuration of the frequency converter according to the first embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 shows an embodiment of the invention described in claim 1 of the present invention. In addition to the configuration of the conventional example, the gain is controlled between the local oscillator 1 and the signal selection circuit 3 by an external control signal. The gain of the amplifier 7 and the amplifiers 6 and 7 are controlled by an external control signal between the amplifier 6, the branch point of the path connected to the local oscillator 2 and another circuit, and the signal selection circuit 3, respectively. The external control signal circuit 8 is provided. With this configuration, when the local oscillator signal f1 of the local oscillator 1 is selected by the signal selection circuit 3, the amplifier 6 provided between the local oscillator 1 and the signal selection circuit 3 by the external control signal 8. Is input to the signal selection circuit 3 by lowering the gain of the amplifier 7 provided between the local oscillator 2 and the frequency selection circuit 3 that generates the unselected local oscillation signal f2. The signal level of the local signal f2 of the unselected frequency is lowered to prevent the local signal f2 from wrapping around the local signal f1 via the collectors of the Tr31 and 32. Further, even if the local oscillation signal f1 sneaks to the input side of the local oscillation signal f2 via the collectors of the Tr 33 and 34, the local oscillation signal f1 is prevented from sneaking into the other circuit block 5 by the amplifier 7. be able to. Similarly, when the local oscillator signal f2 of the local oscillator 2 is selected by the signal selection circuit 3, the gain of the amplifier 7 is increased by the external control signal 8, and the gain of the amplifier 6 is decreased by reducing the gain of the amplifier 6. The input level of the local oscillation signal f1 inputted to the signal is lowered to prevent the local oscillation signal f2 from entering the local oscillation signal f2 through the collector. Thereby, unnecessary spurious generated in the output signal can be reduced.

(Second Embodiment)
FIG. 4 shows an embodiment of the present invention as set forth in claim 2 of the present invention. In the frequency converter of claim 1, at least one local oscillator and the local oscillator are used instead of two or more local oscillators. Two or more frequency dividers 9 and 10 that divide the local oscillation signal output from the local oscillation signal into different frequencies, and an external control signal is provided between the plurality of frequency dividers and the signal selection circuit. The frequency converter is characterized in that an amplifier having means for switching the gain is connected to each other, and the same effect as in the embodiment of the first aspect can be obtained.

(Third embodiment)
FIG. 5 shows an embodiment of the invention described in claim 3 of the present invention. In the frequency converter of claim 1 or 2, a signal having a desired frequency is provided between each amplifier 6, 7 and the signal selection circuit 3. The frequency conversion circuit is provided with filters 11 and 12 that pass only through the filter, and further increases the effects of the inventions of claims 1 and 2.

  As described above, the present invention can provide a useful configuration for a frequency converter that reduces unnecessary spurious included in an output signal in a radio transmission system in which two or more local oscillation frequencies exist.

The block diagram which shows the structure of the frequency converter which concerns on the 1st Embodiment of this invention. Block diagram showing the configuration of a conventional frequency converter The figure which shows the differential amplifier circuit which comprises the signal selection circuit 3 The block diagram which shows the structure of the frequency converter which concerns on the 2nd Embodiment of this invention. The block diagram which shows the structure of the frequency converter which concerns on the 3rd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st local oscillator 2 2nd local oscillator 3 Signal selection circuit 4 Frequency conversion circuit 5 Another circuit block 6 Amplifier 7 Amplifier 8 External control signal circuit 9 Divider 10 Divider 11 Filter 12 Filter 31 Transistor Q1
32 Transistor Q2
33 Transistor Q3
34 Transistor Q4
35 Load resistance R2
36 Load resistance R1
37 Current Source Ioa
38 Current Source Iob
39 differential amplifier circuit 40 differential amplifier circuit

Claims (3)

In a frequency converter comprising at least two or more local oscillators, a signal selection circuit for selecting one local oscillation signal from the local oscillator, and a frequency conversion circuit for frequency converting the local oscillation signal,
The signal selection circuit is composed of at least two or more differential amplifiers sharing a collector and a load,
An amplifier having means for switching the gain by an external control signal is connected between the plurality of local oscillators and the signal selection circuit, and all the amplifiers pass only a desired local signal by the external control signal. A frequency converter characterized by being gain-controlled. 2. The frequency converter according to claim 1, comprising at least one local oscillator and two or more frequency dividers that divide a local oscillation signal output from the local oscillator into local oscillation signals having different frequencies. An amplifier having means for switching the gain by an external control signal is connected between the frequency divider and the signal selection circuit. 3. The frequency converter according to claim 1, further comprising a filter that passes only a signal having a desired frequency between each amplifier and the signal selection circuit.

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