JPH0983253A - Frequency converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the frequency converter which is operated at an input level of a local signal lower than that of a conventional converter so as to eliminate the need for an amplifier amplifying the local signal having been required for the conventional converter thereby preventing increase in power consumption and the number of components. SOLUTION: After an RF signal and a local signal are mixed by a hybrid 3, the mixed signal is given to a gate terminal of a FET 5 through an input matching circuit 4. An IF signal is obtained from a drain terminal of the FET via an output matching circuit 6 and a low pass filter 7. Furthermore, a feedback circuit 9 providing a positive feedback signal is provided between the drain terminal of the FET and the input terminal for a local signal. A circuit having an interdigital capacitor suitable for MMIC processing is used for the feedback circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency converter used in a receiver of a wireless communication device.

[0002]

2. Description of the Related Art Recently, in order to reduce the size of wireless communication devices,
MMICs (microwave monolithic ICs) made of compound semiconductors are often used. In a receiver, a low noise amplifier is often used as an MMIC, and a frequency converter using an FET suitable for the MMIC is also being developed.

Conventionally, as a frequency converter of this type, FIG.
The following are known. In the frequency converter of FIG. 3, the received RF signal is supplied to the first input terminal 1 and the local signal is supplied to the second input terminal 2. The RF signal and the local signal are mixed by a hybrid 3 such as a Lange coupler suitable for MMIC conversion, and applied to the gate terminal of the FET 5 through the input matching circuit 4. On the other hand, the drain terminal of the FET 5 outputs signals of various frequency components including the RF signal and the local signal input to the gate terminal. Only the frequency component of the difference from the frequency is taken out as an IF signal to the IF output terminal 8 through the output matching circuit 6 and the low pass filter 7.

[0004]

At this time, it is well known that the local signal requires a high signal level in order to cause the FET 5 to perform a non-linear operation. As a means for obtaining a high signal level as a local signal, the output level from the oscillator that is the signal source of the local signal is often insufficient, and amplification to the required level is performed using an amplifier or the like. . This has a problem that the power consumption of the amplifier is increased and the number of parts is increased.

Therefore, an object of the present invention is to provide a frequency converter capable of causing a FET to perform a sufficient non-linear operation even when a low level local signal is input.

[0006]

In order to solve the above problems, a frequency converter according to the present invention has a first input terminal to which an RF signal is input and a second input terminal to which a local signal is input. And a signal supply means for supplying the FET with a mixed signal of the RF signal and the local signal to the gate terminal of the FET, and a signal extraction for extracting a specific signal from the FET output signal output from the drain terminal of the FET. And a feedback circuit for returning a part of the local signal included in the FET output signal to the second input terminal.

[0007]

According to the frequency converter having the above structure, the FE
Since a part of the local signal included in the output of the drain terminal of T is fed back to the second input terminal, it is possible to cause the FET to perform a sufficient non-linear operation even when the local signal of a low level is input. It will be possible.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. A frequency converter according to an embodiment of the present invention is shown in FIG.

As shown in FIG. 1, this frequency converter is
A first input terminal 1, a second input terminal 2, a hybrid 3 connected to the first and second input terminals 1 and 2, and an input matching circuit 4 connected to the hybrid 3.
And an FET 5 connected to the input matching circuit 4, an output matching circuit 6 connected to the FET 5, and a low-pass filter 7 connected to the output matching circuit 6 for extracting only a necessary frequency component. There is.

The received RF signal is input to the first input terminal 1,
The local signal is also supplied to the second input terminal 2. The RF signal and the local signal are mixed by the hybrid 3 to form a mixed signal, which is applied to the gate terminal of the FET 5 through the input matching circuit 4 for matching the mixed signal. On the other hand, the drain terminal of FET5
Signals of various frequency components including the RF signal and the local signal input to the gate terminal are output as the FET output signal. From this FET output signal, only the frequency component of the difference between the frequency of the RF signal and the frequency of the local signal, which is necessary for the frequency converter, is taken out to the IF output terminal 8 as an IF signal through the output matching circuit 6 and the low pass filter 7. That is, the output matching circuit 6 and the low-pass filter 7
Together, they constitute signal extraction means. Here, the output matching circuit 6 is for matching the FET output signal, and the low pass filter 7 is for filtering the output signal of the output matching circuit 6.

Further, the frequency converter takes out a part of the local signal included in the FET output signal outputted to the drain terminal of the FET 5 from the drain terminal and makes a positive feedback to the second input terminal 2. A feedback circuit 9 is provided for feedback. As the feedback circuit 9, it is possible to use an interdigital capacitor suitable for forming an MMIC as shown in FIG. 2 to which a line whose electric length is optimized so that the feedback circuit is a positive feedback is connected.

Due to the effect of positive feedback, the local signal input to the FET 5 can cause the FET 5 to perform a non-linear operation even at a low signal level as compared with the case where there is no positive feedback. The frequency conversion can be performed in the lower case.

FIG. 3 shows an example of characteristics showing the effect of the present invention. In FIG. 3, the conversion gain of the frequency converter with respect to the input level of the local signal is shown in comparison with the conventional example. From this, it can be seen that the present invention can obtain a conversion gain equal to that of the related art when the input level of the local signal is smaller than that of the related art.

[0014]

As described above, according to the present invention,
Since a part of the local signal included in the signal output to the drain terminal of the FET is taken out from the drain terminal and is fed back to the terminal for inputting the local signal so as to be positive feedback , When the input level of the local signal is smaller than the conventional level, the conversion gain equal to the conventional level can be obtained. Therefore, it is not necessary to use an amplifier or the like for obtaining a large signal level as a local signal, and the number of parts does not increase.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a frequency converter according to an embodiment of the present invention.

FIG. 2 is a diagram showing an embodiment of a feedback circuit for constituting the present invention.

FIG. 3 is a diagram showing the effect of the present invention.

FIG. 4 is a block diagram showing a configuration of a conventional frequency converter.

[Explanation of symbols]

 1 First Input Terminal 2 Second Input Terminal 3 Hybrid 4 Input Matching Circuit 5 FET 6 Output Matching Circuit 7 Low Pass Filter 8 IF Output Terminal 9 Feedback Circuit

Claims (5)

[Claims] 1. A first input terminal for inputting an RF signal, a second input terminal for inputting a local signal, and an FET.
A signal supplying means for mixing the RF signal and the local signal and supplying the mixed signal to the gate terminal of the FET;
In a frequency converter having a signal extracting means for extracting a specific signal from the FET output signal output from the drain terminal of ET, a part of the local signal included in the FET output signal is fed back to the second input terminal. A frequency converter comprising a feedback circuit for controlling the frequency. 2. The signal supply means includes a hybrid for mixing the RF signal and the local signal to obtain a mixed signal, and an input matching circuit for matching the mixed signal. The described frequency converter. 3. The signal extracting means has an output matching circuit for matching the FET output signals.
The described frequency converter. 4. The frequency converter according to claim 3, further comprising a low-pass filter for filtering an output signal of the output matching circuit. 5. The frequency converter according to claim 1, wherein the feedback circuit has an interdigital capacitor.