JP2007180621A - Frequency converter and frequency conversion method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology for adjusting power of a local oscillation signal in a frequency converter for converting a received intermediate frequency band modulation signal into a wireless frequency band signal. <P>SOLUTION: The frequency converter is equipped with: a power distribution means 21 for distributing a local oscillation signal 24 into first and second local oscillation signals; a mixer means 20 that receives the first local oscillation signal and the intermediate frequency band modulation signal, multiplies them, and converts the product into a single side band (SSB) modulation signal or a double side band (DSB) modulation signal; a variable attenuator means 22 capable of adjusting the power of the second local oscillation signal; and a power composite means 23 for composing a mixer output signal from the mixer means with an attenuator output signal from the variable attenuator means. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a low-cost and high-stable radio frequency band (RF) front-end technology, and more particularly, to a technology related to the configuration of a mixer that performs frequency conversion.

  In designing a mixer circuit that performs frequency conversion, it is necessary to satisfy many required specifications. In addition to general problems such as conversion efficiency and noise figures, it is desirable to sufficiently suppress spurious components that become out-of-band radiation and unwanted radiation in the RF transmission output at the mixer output.

In a known general up-converter, it is important that one of the local oscillation signal and the up-converted sideband signal is sufficiently suppressed from the viewpoint of effective use of frequency resources.
For this reason, research and development in wireless communication so far has focused on improving the performance of balanced mixers that remove local oscillation signal components from mixer outputs and image rejection mixers that remove one-sideband components.

  FIG. 7 shows a configuration of a wireless communication system proposed by the present applicants, and performs self-heterodyne communication between a transmitter (100) and a receiver (110). The self-heterodyne system is disclosed in Patent Documents 1 to 3, Non-Patent Document 1, and the like.

The self-heterodyne method will be described with reference to FIG. 7. First, the transmitter (100) is provided with an IF signal generation unit for generating an intermediate frequency band modulation signal, or an IF signal is input as shown in the figure. Then, the mixer (101) multiplies the IF signal and the local oscillation signal generated by the local oscillator (102) to obtain a radio modulation signal.
A filter (bandpass filter) (103) for removing unnecessary components (103) and an amplifier (104) are sent from the antenna (105).

  At this time, according to the self-heterodyne system, the signal is converted into a carrier non-suppressed single sideband (SSB) modulation signal (120) or a double sideband (DSB) modulation signal (121) and transmitted to the receiver. In the receiver (110), the transmission signal is received by the antenna (111), amplified by the amplifier (112), passed through the filter (113), and the radio modulated signal received using the received unmodulated carrier is reduced to the intermediate frequency band. In order to convert, these are detected together, for example using a squarer (114). In this case, the signal spectrum immediately before the filter (115) is as shown in (122), and an unnecessary component due to secondary distortion occurs in the low frequency band. This is removed by the filter (115), and the IF signal is output.

  In such a self-heterodyne method, the transmitter transmits the local oscillation signal together with the modulation signal, and the receiver performs down-conversion of the radio modulation signal using the received local oscillation signal, thus simplifying the configuration of the receiver. In particular, there is an advantage that a local oscillator whose phase and frequency are stabilized with high accuracy need not be provided in the transmitter and the receiver.

  Incidentally, a conventional mixer circuit used in a wireless communication system is as shown in FIG. An IF signal (210) which is a data modulation signal input from the IF signal input port (201) is input to the 90-degree hybrid coupler (200). As a result, the IF signal having a phase difference of 0 degree and −90 degrees with respect to the input IF signal is multiplied with the local oscillation signal of the same phase in the mixers (202) and (203), frequency-converted, and again 90 degrees. Synthesized by the hybrid coupler (201). From the above, it is possible to take out the port from which mainly the upper-band radio frequency band modulation signal (RF signal) (207) is output and the port from which mainly the lower-side band RF signal (208) is output. .

When the signal spectrum of the upper sideband RF signal is a desired spectrum, the lower sideband signal and the unmodulated carrier need to be sufficiently suppressed as in the signal spectrum (211). In order to perform suppression with high accuracy in this way, in the 90-degree hybrid couplers (200) and (206), equal power distribution of the modulation signal to each mixer and equal power coupling of the modulation signal from the mixer are performed. At the same time, it is necessary to maintain a phase difference of 90 degrees with high accuracy over the modulation frequency band. Further, it is necessary to input the local oscillation signal (204) to both mixers (202) and (203) in a completely in-phase state by the in-phase distributor (205).
Such a conventional balance type mixer or image elimination balance mixer naturally does not require the local carrier signal to remain, so that it is not necessary to control the output intensity.

  On the other hand, as an example of the mixer circuit used in the self-heterodyne system, a configuration as shown in FIG. 9 is adopted. That is, using the Wilkinson distributor (300), a signal having a frequency half that of the local oscillation signal (1/2 local oscillation signal) is input to the mixers (302) and (303). Although the circuit configuration is as shown in the figure, an IF signal (310) having a phase difference of 90 degrees and a 1/2 local oscillation signal are inputted and frequency-converted into an RF signal, and a 90-degree branch line coupler (304) To synthesize.

In the signal spectrum (311) obtained as a result, an unmodulated carrier remains, and this RF signal is transmitted by a self-heterodyne transmitter.
At this time, the intensity of the unmodulated carrier is determined by the design of the mixer, but cannot be changed after manufacture.

JP 2001-53640 A JP 2003-264470 A Japanese Patent No. 3564480 Y. Shoji, K. Hamaguchi and H. Ogawa, "Millimeter-wave remote self-heterodyne system for extremely stable and low-cost broadband signal transmission,", IEEE. Trans. Microwave Theory Tech. Vol. 50, pp. 1458, June 2002

In the self-heterodyne system, the applicant's research has revealed that the power balance between both the local oscillation signal component and the radio modulation signal component affects the transmission signal quality. It is desirable to adjust the power. However, the conventional mixer as shown in FIG. 9 has a problem that power adjustment cannot be performed after manufacturing, and it is difficult to obtain optimum conditions.
Therefore, an object of the present invention is to provide a technique that enables power adjustment of a local oscillation signal in a frequency converter that converts an input intermediate frequency band signal into a radio frequency band signal.

The present invention uses the following means in order to solve the above problems.
That is, the invention described in claim 1 relates to a frequency converter that converts an intermediate frequency band modulation signal into a radio frequency band modulation signal. The frequency converter receives the first local oscillation signal, the power distribution means for distributing the local oscillation signal to the second local oscillation signal, the first local oscillation signal, and the intermediate frequency band modulation signal. A mixer means for multiplying and converting to a single sideband (SSB) modulated signal or a double sideband (DSB) modulated signal; a variable attenuator means capable of adjusting the power of the second local oscillation signal; Power combining means for combining the mixer output signal and the attenuator output signal from the variable attenuator means is provided.
A frequency converter capable of adjusting the power of the local oscillation signal component by this configuration is provided.

  According to a second aspect of the present invention, in the frequency converter according to the first aspect, the mixer means used is an image elimination balance mixer.

  According to a third aspect of the present invention, in the frequency converter according to the first aspect, the mixer means used is an Nth-order harmonic mixer, and an Nth-order frequency multiplier circuit is provided before or after the variable attenuator means. It is characterized by providing.

The invention according to claim 4 can provide a frequency converter having a configuration different from that of claim 1. This configuration includes a dividing unit that receives a 1/2 local oscillation signal, which is 1/2 the frequency of the local oscillation signal, and equally divides the first and second 1/2 local oscillation signals in phase with each other; Subharmonic type first FET (field effect transistor) mixer means for inputting the first 1/2 local oscillation signal and the intermediate frequency band signal of the first phase, and the second 1/2 local oscillation A sub-harmonic type second FET mixer means for inputting a signal and an intermediate frequency band signal having a phase difference of π / 2 with respect to the first phase; an output from the first FET mixer means; An image rejection type frequency converter comprising 90-degree hybrid coupling means for inputting the output from the FET mixer means.
The FET mixer means is provided with an adjustment bias circuit for adjusting the local oscillation signal component.

  According to a fifth aspect of the present invention, in the frequency converter according to the fourth aspect, the FET mixer means inputs the 1/2 local oscillation signal and the intermediate frequency band signal to the gate so that the local frequency is output. A single-ended type mixer obtained simultaneously with an oscillation signal component and a radio frequency band signal frequency-converted to an intermediate frequency band signal by the frequency component, and further, the gate input section is the adjustment bias circuit. A gate bias voltage application circuit; and a drain bias voltage application circuit that applies a fixed voltage to the drain.

  And a connection point for connecting the input of the 1/2 local oscillation signal, the input from the adjustment gate bias voltage applying circuit, and the input of the intermediate frequency band signal through a predetermined bias circuit; A frequency converter comprising a gate connected to the connection point, a grounded source, and a FET having a drain applied by the drain bias voltage application circuit and provided with a mixer output terminal.

The present invention can also provide a frequency conversion method for converting an intermediate frequency band modulation signal into a radio frequency band modulation signal.
In this method, a local oscillation signal is divided into a first local oscillation signal and a second local oscillation signal, the first local oscillation signal and the intermediate frequency band modulation signal are input and multiplied, and a single side wave is obtained. It converts into a band (SSB) modulation signal or a double sideband (DSB) modulation signal, and adjusts and synthesizes the power of the second local oscillation signal.

  According to the seventh aspect of the present invention, there is provided a frequency conversion method having a configuration different from the above, wherein (1) a ½ local oscillation signal having a frequency ½ of the local oscillation signal is input and the phase conversion method is mutually in phase. The first and second half local oscillation signals are equally divided, and (2) the first half local oscillation signal and the intermediate frequency band signal of the first phase are sub-harmonic type first FETs. (3) Subharmonic type second FET mixer means that inputs the second half local oscillation signal and the intermediate frequency band signal having a phase difference of π / 2 from the first phase. (4) An image rejection type frequency converter configuration is used in which the output from the first FET mixer means and the output from the second FET mixer means are input to the 90-degree hybrid coupling means. The adjustment bias circuit of the FET mixer means adjusts and controls the power of the local oscillation signal component at the output of the frequency converter.

Furthermore, the invention according to claim 8 can provide a self-heterodyne transmitter. That is, the transmitter generates an unmodulated carrier and a radio modulated signal when converting the intermediate frequency band signal into a radio modulated signal, radiates both signals from the antenna, and the receiver receives the unmodulated carrier and the radio signal received by the antenna. This is a transmitter used in a self-heterodyne communication system that generates a product component with a modulation signal and converts it into an intermediate frequency band signal.
The frequency converter according to any one of claims 1 to 5 is provided as a frequency conversion means of the transmitter to generate a radio modulation signal.

  According to the present invention, when a local oscillation signal is converted into a radio frequency band signal, the power of the local oscillation signal component can be adjusted by a simple control method. As a result, the power ratio between the local oscillation signal and the modulation signal can be adjusted at any time to obtain an optimum value, thereby providing a technique that contributes to a low-cost and highly stable communication method.

Hereinafter, embodiments of the present invention will be described based on examples shown in the drawings. The embodiment is not limited to the following.
FIG. 1 is an explanatory diagram for explaining the function of a frequency converter (mixer circuit) (1) used in the present invention. The mixer circuit (1) receives the IF band modulation signal (10) and the local oscillation signal (11) generated by the local oscillator. Then, a carrier non-suppression single sideband (SSB) modulation signal is output from the RF band output port (12).

In the signal spectrum at this time, the image of the lower sideband signal (13) or the like is removed, and the ratio to the carrier is suppressed to a desired level (for example, 33 dBc in the figure).
Intermediate frequency band modulated signal frequency f _IF at the mixer is a multiplier, as is known, is converted to a frequency f _{LO + IF} the upper sideband signal (15) by an unmodulated carrier of frequency f _LO (14).

  According to the applicant's research, the carrier-to-noise power ratio (CN ratio) of the IF signal detected by the square detection method in the receiver circuit in the self-heterodyne method is the local oscillation signal (14) component / modulation signal (15) component. It is known that the correlation shown in FIG. As is apparent from the graph, when the power of the local oscillation signal (14) and the modulation signal (15) are equal, the CN ratio is maximized, which is optimal in the communication method. Accordingly, the idea of the present invention is that the optimum condition can be realized if the signal intensity of the local oscillation signal can be controlled in the mixer circuit (1).

Example 1
As a first embodiment of the present invention, FIG. 2 shows a configuration diagram of a mixer circuit. The circuit includes an image removal balance mixer (20), a power distributor (21), a voltage adjustment type RF attenuator (22), and a combiner (23).

  The local oscillation signal (24) is distributed by the power distributor (21), and one is used for frequency up-conversion in the mixer (20). The configuration of an image removal balance mixer is well known, and a configuration capable of sufficiently suppressing an image signal and a local oscillation signal has already been provided. The signal spectrum (26) of the input IF signal and the signal spectrum (27) of the output signal after passing through the mixer are as shown in the figure.

  The other local oscillation signal (24) distributed is combined with the output signal from the mixer (20) in the combiner (23). As a result, a transmission signal composed of the local oscillation signal and the modulation signal necessary for the self-heterodyne method is generated. The signal spectrum (28) of the transmission signal is as shown in the figure.

By providing the attenuator (22), the power of the local oscillation signal can be changed only by adjusting the DC voltage (25). A configuration example of the attenuator (22) is shown in FIG.
In this configuration, the local oscillation signal input from the input terminal (30) is subjected to a change in voltage applied to the DC bias control terminal (31), so that the coil (32), the capacitors (33 to 36), the resistance (37 · 38), the power is adjusted by this circuit comprising the PIN diodes (39, 40), and is output from the output terminal (41).

This configuration can be mounted on a single chip as a monolithic microwave integrated circuit (MMIC), which simplifies the configuration and contributes to cost reduction.
Note that such an attenuator circuit is known, and a known attenuator can be used as appropriate in the present invention. The variable in the attenuator is not limited to changing the voltage, and any configuration such as a method of changing the resistance value may be used.

  As another embodiment, a sub-harmonic mixer or an Nth-order harmonic mixer may be used for the mixer (20), and a doubler circuit or an Nth-order frequency multiplier circuit may be provided before or after the attenuator (22).

  With the above configuration, the power of the local oscillation signal can be easily adjusted, and an optimum CN ratio can be obtained in the self-heterodyne system. In particular, the power of the local oscillation signal and the modulation signal can be adjusted independently. In addition, since an optimized mixer can be used as an existing image removal balance mixer, it can be realized at a low cost, and at the same time, high linearity performance in frequency conversion can be expected.

(Example 2)
As the second embodiment of the present invention, a circuit configuration as shown in FIG. 4 can be adopted. In this configuration, unlike the configuration of FIG. 2, sub-harmonic type frequency conversion is performed.
In FIG. 4, a signal having a frequency half that of the local oscillation signal (hereinafter referred to as a 1/2 local oscillation signal) (50) is input to an in-phase divider (51) that is a dividing means, and two systems in phase. Is divided into two signals.

An intermediate frequency band signal is input to one mixer circuit (52), and an intermediate frequency band signal having a phase difference of 90 degrees (π / 2) is input to the other mixer circuit (53).
Then, the output signals frequency-converted by the mixer circuits (52) and (53) are input to the 90-degree hybrid coupler (54), synthesized, and output from the output terminal (55).

  This configuration is an extension of the conventional example shown in FIG. 9, but in the technique of FIG. 9, the capacitances of the two diodes (312) (313) used in the mixers (302) and (303) are adjusted. Thus, the output of the local oscillation signal was determined and could not be adjusted flexibly after circuit design.

FIG. 5 shows a detailed circuit configuration example of the mixers (52) and (53) shown in FIG. In the circuit proposed in the present invention, the mixer (52) (53) shown in FIG. 4 is a mixer circuit using a single-ended type FET (field effect transistor), and the local oscillation signal component is controlled by bias control of the FET. Makes the power adjustable.
The 1/2 local oscillation signal (60) and the intermediate frequency band signal (61) are input to the gate (66) of the FET, and the up-converted radio modulation signal and local oscillation signal are supplied to the drain (69) of the FET. And output from the output port (65).

  At this time, an adjustment bias circuit via a matching circuit (63) is provided in the gate (66), and an adjustable control voltage (62) is applied. This voltage causes local oscillation. The power from the signal output port (65) can be varied.

  The most basic configuration of this circuit is as described above. In addition, a constant voltage (70) is applied to the drain (69), the source (67) is grounded, and a plurality of matching circuits (64) are provided. (71) is arranged.

In single-ended type mixers, it is well known that frequency conversion factors strongly depend on the FET gate bias setting. Generally, this circuit outputs 2f _LO + f as a desired signal. _An ideal gate bias condition is selected in which the output signal having the _IF frequency is maximized and the output signal having the 2f _LO frequency and other frequency components treated as unnecessary components is minimized.

FIG. 11 is a graph showing an example of the relationship between the applied voltage at the gate bias and the ratio of the local oscillation signal and the modulation signal. In the figure, as the transmission signal in the self-heterodyne system to which the present embodiment is assumed, for example, a graph of the frequency of the signal 2f _LO, the intersection A and B with the graph of 2f _LO + f _IF frequency signal optimum It is known that this is a point, and in the present invention, a voltage having a value at this time may be applied.

  Thus, it is easy to adjust and control the balance between the two signals by finding the optimum gate bias condition. In addition, by adjusting the two FETs respectively, the two FETs can be made to perform sufficient image removal.

FIG. 6 is a circuit configuration example of a frequency converter provided by the present invention when a mixer circuit using FETs is mounted in a balanced manner, and the same components as those in FIG. 4 are denoted by the same reference numerals. Similarly in this circuit, the 1/2 local oscillation signal (50) is distributed by the in-phase divider (51) and connected to each connection point via the matching circuit (501). In addition, an intermediate frequency band signal via the matching circuit (504) and an adjustable bias voltage (500a) via the matching circuit (502) are input to the one connection point from the input port (503a). The
The other connection point includes a signal obtained by shifting the phase of the intermediate frequency band signal from the input port (503b) via the matching circuit (504) by π / 2 and an adjustable bias voltage via the matching circuit (502). (500b) is input.

  Further, the connection point is connected to the gate via the matching circuit (505). As described above, the source (506) is grounded, and a constant voltage (508) is input to the drain via the bias circuit using the matching circuit (509), and a signal is output from the drain.

In this embodiment, a configuration using a sub-harmonic mixer can be provided, so that a configuration using a low-frequency local oscillation signal can be taken. As a result, frequency stabilization and cost reduction can be achieved.
In the above-described embodiment, an example in which the signal is converted into a single sideband (SSB) modulation signal is shown. However, in the case of conversion into a double sideband (DSB) modulation signal, the circuit configuration of the frequency converter becomes a simpler configuration. . That is, it is not necessary to take a balanced configuration.

The present invention provides the frequency converter as described above, and may be provided as a frequency conversion method for performing frequency conversion by the method as described above.
Further, it is particularly suitable to be used in a communication system using a self-heterodyne system as shown in FIG. 7, and the frequency converter of the present invention can be used for the mixer (101) of the transmitter.

It is explanatory drawing explaining the function of the mixer which concerns on this invention. 1 is a circuit diagram of a mixer circuit according to a first embodiment of the present invention. It is a circuit diagram of an attenuator. It is a circuit diagram of the mixer circuit which concerns on the 2nd Embodiment of this invention. 2 is a circuit diagram of a mixer using an FET. FIG. 2 is a circuit diagram of a mixer circuit in which a mixer using an FET is mounted. FIG. It is explanatory drawing explaining the outline | summary of a self heterodyne. It is a circuit diagram explaining the circuit of the conventional mixer. It is a circuit diagram explaining the circuit of the mixer used by the conventional self heterodyne. It is a graph which shows the correlation of the power ratio of a local oscillation signal and a modulation signal, and CN ratio in self heterodyne. It is a graph for calculating | requiring the optimal gate bias condition in the 2nd Embodiment of this invention.

Explanation of symbols

20 mixer 21 distributor 22 attenuator 23 synthesizer 24 local oscillation signal 25 DC voltage 26 signal spectrum of IF signal 27 signal spectrum of signal output from mixer 28 signal spectrum of signal synthesized by synthesizer

Claims (8)

A frequency converter for converting an intermediate frequency band modulation signal into a radio frequency band modulation signal,
Power distribution means for distributing the local oscillation signal to the first local oscillation signal and the second local oscillation signal;
Mixer means for inputting and multiplying the first local oscillation signal and the intermediate frequency band modulation signal and converting the first local oscillation signal and the intermediate frequency band modulation signal into a single sideband (SSB) modulation signal or a double sideband (DSB) modulation signal;
Variable attenuator means capable of adjusting the power of the second local oscillation signal;
Power combining means for combining the mixer output signal from the mixer means and the attenuator output signal from the variable attenuator means;
A frequency converter that can adjust the power of the local oscillation signal component. The frequency converter according to claim 1, wherein the mixer means is an image removal balance mixer. The mixer means is an Nth harmonic mixer,
The frequency converter according to claim 1, wherein an Nth-order frequency multiplication circuit is provided at a front stage or a rear stage of the variable attenuator means. A frequency converter for converting an intermediate frequency band modulation signal into a radio frequency band modulation signal,
A dividing means for inputting a ½ local oscillation signal, which is a ½ frequency of the local oscillation signal, and equally dividing the first and second 1/2 local oscillation signals in phase with each other;
Sub-harmonic type first FET (field effect transistor) mixer means for inputting the first 1/2 local oscillation signal and the first phase intermediate frequency band signal;
Sub-harmonic type second FET mixer means for inputting the second 1/2 local oscillation signal and an intermediate frequency band signal having a phase difference of π / 2 with the first phase;
An image rejection type frequency converter comprising 90 degree hybrid coupling means for inputting the output from the first FET mixer means and the output from the second FET mixer means,
A frequency converter capable of adjusting the power of the local oscillation signal component, characterized in that an adjustment bias circuit for adjusting the local oscillation signal component is provided in the FET mixer means. The FET mixer means,
By inputting the 1/2 local oscillation signal and the intermediate frequency band signal to the gate, the local oscillation signal component at the output and the radio frequency band signal frequency-converted to the intermediate frequency band signal by the frequency component can be obtained simultaneously. A single-ended type mixer, the gate input section further comprising an adjustment gate bias voltage application circuit that is the adjustment bias circuit, and a drain bias voltage application circuit that applies a fixed voltage to the drain,
A connection point for connecting each of the input of the 1/2 local oscillation signal, the input from the adjustment gate bias voltage application circuit, and the input of the intermediate frequency band signal through a predetermined matching circuit; The frequency converter according to claim 4, comprising: a gate connected to the connection point; a grounded source; and an FET having a drain applied by the drain bias voltage application circuit and provided with a mixer output terminal. A frequency conversion method for converting an intermediate frequency band modulation signal into a radio frequency band modulation signal,
Distributing the local oscillation signal to the first local oscillation signal and the second local oscillation signal;
The first local oscillation signal and the intermediate frequency band modulation signal are input and multiplied, and converted into a single sideband (SSB) modulation signal or a double sideband (DSB) modulation signal,
A frequency conversion method comprising adjusting and synthesizing the power of the second local oscillation signal. A frequency conversion method for converting an intermediate frequency band modulation signal into a radio frequency band modulation signal,
A 1/2 local oscillation signal that is 1/2 the frequency of the local oscillation signal is input and equally divided into first and second 1/2 local oscillation signals that are in phase with each other,
The first 1/2 local oscillation signal and the intermediate frequency band signal of the first phase are input to the subharmonic first FET mixer means,
The second 1/2 local oscillation signal and an intermediate frequency band signal having a phase difference of π / 2 with the first phase are input to a second harmonic mixer device of sub-harmonic type,
An image rejection type frequency converter configuration in which an output from the first FET mixer means and an output from the second FET mixer means are input to a 90-degree hybrid coupling means,
A frequency conversion method comprising adjusting and controlling the power of a local oscillation signal component at the output of a frequency converter by an adjustment bias circuit of the FET mixer means. When a transmitter converts an intermediate frequency band signal into a radio modulated signal, it generates an unmodulated carrier and a radio modulated signal, radiates both signals from the antenna, and an unmodulated carrier and radio modulated signal received by the receiver at the antenna. In the transmitter used in the communication system of the self-heterodyne method that converts to an intermediate frequency band signal by generating a product product with
6. A self-heterodyne transmitter comprising the frequency converter according to claim 1 to generate a radio modulation signal.

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