JP2914426B2 - Frequency converter - Google Patents

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 for a receiver of a wireless communication device.

[0002]

2. Description of the Related Art In recent years, to reduce the size of wireless communication devices,
An MMIC (microwave monolithic IC) using a compound semiconductor is 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 developed.

Conventionally, as a frequency converter of this type, FIG.
The following are known. In the frequency converter of FIG. 3, a received RF signal is supplied to a first input terminal 1 and a local signal is supplied to a 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, and applied to the gate terminal of the FET 5 through the input matching circuit 4. On the other hand, since signals of various frequency components including the RF signal and the local signal input to the gate terminal are output to the drain terminal of the FET 5, the frequency of the RF signal and the local signal required for the frequency converter are output. Only the frequency component of the difference from the frequency is extracted as an IF signal to an IF output terminal 8 through an output matching circuit 6 and a low-pass filter 7.

[0004]

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

It is therefore an object of the present invention 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]

To solve the above-mentioned problems, a frequency converter according to the present invention comprises a first input terminal for receiving an RF signal and a second input terminal for receiving a local signal. An FET, a signal supply means for mixing the RF signal and the local signal and supplying the mixed 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 configuration, the FE
Since 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 nonlinear operation even when a low-level local signal is input. It becomes possible.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a frequency converter according to an embodiment of the present invention.

As shown in FIG. 1, this frequency converter
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 necessary frequency components. I have.

[0010] The received RF signal is supplied to a first input terminal 1.
The local signals are supplied to the second input terminals 2 respectively. 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 an 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 FET output signals. 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 required as a frequency converter is extracted as an IF signal to an IF output terminal 8 through an output matching circuit 6 and a low-pass filter 7. That is, the output matching circuit 6 and the low-pass filter 7
Together constitute signal extraction means. Here, the output matching circuit 6 is for matching the output signal of the FET, and the low-pass filter 7 is for filtering the output signal of the output matching circuit 6.

Further, the frequency converter extracts a part of the local signal included in the FET output signal output to the drain terminal of the FET 5 from the drain terminal, and provides a positive feedback to the second input terminal 2. Is provided with a feedback circuit 9 for performing feedback. As the feedback circuit 9, a circuit in which an interdigital capacitor suitable for MMIC as shown in FIG. 2 is connected to a line whose electrical length is optimized so that the feedback circuit has a positive feedback can be used.

The local signal input to the FET 5 can cause the FET 5 to perform a non-linear operation even at a signal level lower than that without the positive feedback due to the effect of the positive feedback. The frequency conversion can be performed at a lower frequency.

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

[0014]

As described above, according to the present invention,
Because a part of the local signal included in the signal output to the drain terminal of the FET is extracted from the drain terminal, and the feedback is performed so that the terminal for inputting the local signal becomes a positive feedback. In the case where the input level of the local signal is lower than the conventional one, a conversion gain equal to the conventional one 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 components does not increase.

[Brief description of the 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 one 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]

 REFERENCE SIGNS LIST 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)

(57) [Claims] A first input terminal for receiving an RF signal, a second input terminal for receiving a local signal, and an FET.
Signal supply means for mixing the RF signal and the local signal and supplying the mixed signal to the gate terminal of the FET;
A signal extracting means for extracting a specific signal from the FET output signal output from the drain terminal of the ET, wherein 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 causing the frequency converter to operate. 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 frequency converter as described. 3. The signal output means has an output matching circuit for matching the output signal of the FET.
The frequency converter as described. 4. The frequency converter according to claim 3, further comprising a low-pass filter for filtering an output signal of said output matching circuit. 5. The frequency converter according to claim 1, wherein said feedback circuit has an interdigital capacitor.