JP2002290156A - Method for automatically controlling mixer operation point, and frequency converter circuit used therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a frequency converter circuit for automatically controlling a mixer operation point to be optimum. SOLUTION: A variable attenuator 1 attenuates an inputted local oscillation frequency (LO) signal. A buffer amplifier 2 has a prescribed gain. A distributor 3 branches the output of the buffer amplifier 2 into two. The two-branched signals and an intermediate frequency(IF) signal which is of the same in level are inputted to harmonic mixers 4 and 5. Detection circuits 6 and 7 respectively detect the outputs of the harmonic mixers 4 and 5. A control circuit 8 detects the difference in detected voltages of the outputs in the detection circuits 6 and 7 and controls the amount of attenuation in the variable attenuator 1 so as to make the detected voltages equal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency conversion circuit, and more particularly to a frequency conversion circuit capable of automatically controlling an input level of a mixer to an optimum level.

[0002]

2. Description of the Related Art A conventional frequency conversion circuit sets an input level of a local oscillation frequency (LO) signal for increasing a conversion gain as much as possible and reducing a generated distortion rate as much as possible. It is configured to extract the output level of a radio frequency (RF) signal according to the magnitude of the input level.

In order to keep the input level of the LO signal constant, a method of using a buffer amplifier inserted on the LO input side in a state where the output level is saturated or incorporating output level control into the buffer amplifier alone is adopted. I have been.

However, in such a method, the optimum level is determined based on the conversion efficiency characteristic of the mixer and the generated distortion characteristic, while taking into account the output fluctuation due to the temperature of the buffer amplifier and the decrease in reliability due to excessive input to the buffer amplifier. Had to be adjusted.

[0005]

When the conventional frequency conversion circuit described above is used in an optimum state based on the conversion efficiency characteristics and distortion characteristics of the mixer, the output fluctuation due to the temperature of the buffer amplifier and the output of the buffer amplifier may be reduced. However, there is a disadvantage that the adjustment has to be made while taking into account the decrease in reliability due to excessive input.

An object of the present invention is to eliminate the above-mentioned conventional drawbacks by using two mixers to set the level of the local oscillation frequency signal to be inputted to different levels, and to detect the detection voltages of the two mixers. An object of the present invention is to provide a frequency conversion circuit capable of automatically controlling a mixer operating point to an optimum level by equalizing the difference.

[0007]

According to the method of automatically controlling a mixer operating point according to the present invention, an input signal having the same level and a local oscillation frequency signal having a different level are input to each of a first mixer and a second mixer. Detecting output signals of the first mixer and the second mixer, generating a control signal corresponding to a difference between the detected voltages, and controlling the first mixer so that the difference between the detected voltages becomes equal. And the level of the local oscillation frequency signal input to the second mixer is controlled equally.

Further, in the automatic control method of the mixer operating point according to the present invention, the input signal of the same intermediate frequency and the local oscillation frequency signal of the different level are respectively supplied to the first harmonic mixer and the second harmonic mixer. Input, detects the output signals of the first harmonic mixer and the second harmonic mixer, respectively, generates a control signal corresponding to the difference between the detected voltages, and generates the control signal according to the difference between the detected voltages. The level of the local oscillation frequency signal input to the first harmonic mixer and the second harmonic mixer is controlled to be equal.

Further, the frequency conversion circuit according to the present invention comprises an amplifying means for amplifying the input local oscillation frequency signal, a distribution means for dividing the output of the amplifying means into two, and an intermediate frequency having the same level as that of the divided signal. First and second mixer means for inputting signals respectively, first and second detection means for detecting the outputs of the first and second mixer means, respectively, and outputs of the first and second detection means. And a level control means for outputting a control signal for controlling the output level of the amplifying means so that the difference between the detected voltages becomes equal.

Further, the amplifying means comprises a variable attenuator for attenuating the local oscillation frequency signal and a buffer amplifier having a predetermined gain.

Further, the distribution means is characterized in that the level of the two-branched signal has a preset level difference.

Further, the first and second mixer means are harmonic mixers.

Further, the first mixer means is characterized in that the local oscillation frequency signal having a higher level is inputted and an output signal is taken out.

Further, the second mixer means is characterized in that the local oscillation frequency signal having a lower level is inputted and the output side is terminated.

[0015]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing one embodiment of the frequency conversion circuit of the present invention.

The present embodiment shown in FIG. 1 includes a variable attenuator 1 for attenuating an input local oscillation frequency (LO) signal,
A buffer amplifier 2 having a predetermined gain, a distributor 3 for branching the output of the buffer amplifier 2 into two, and harmonic mixers 4 and 5 for respectively inputting an intermediate frequency (IF) signal having the same level as the branched signal. , Harmonic mixers 4, 5, and detection circuits 6, 7, respectively, and control for detecting the difference between the detection voltages of the outputs of the detection circuits 6, 7 and controlling the variable attenuator 1 so that the difference between the detection voltages becomes equal. And a circuit 8.

Next, the operation of the frequency conversion circuit according to the present embodiment will be described in detail with reference to FIG.

Referring to FIG. 1, the variable attenuator 1 controls the amount of attenuation of an input LO signal by a control signal output from a control circuit 8.

The buffer amplifier 2 amplifies the output of the variable attenuator 1 to a predetermined output level.

The distributor 3 splits the output of the buffer amplifier 2 into two and supplies it to the harmonic mixers 4 and 5. The distributor 3 is set in advance so that the two output levels are different.

The harmonic mixers 4 and 5 receive the LO signal branched into two from the distributor 3 and the IF signal of the same level, and output a frequency-converted radio frequency (RF) signal.

The detection circuits 6 and 7 output detection voltages obtained by detecting a part of the RF signal extracted by the directional coupler.

The control circuit 8 receives the detection voltages output from the detection circuits 6 and 7, detects the potential difference between the two detection voltages, amplifies the detected voltage to a controllable voltage, and supplies the controllable voltage to the variable attenuator 1 to supply the LO signal. Control the level of

Next, the automatic control operation of this embodiment will be described with reference to FIGS. FIG. 2 is a characteristic diagram showing an output level of an RF signal and a distortion rate with respect to an input level of an LO signal of a harmonic mixer. FIG.
FIG. 7 is a characteristic diagram showing a detection voltage output of a detection circuit with respect to an input level of an LO signal.

According to FIG. 2, the harmonic mixers 4, 5
When the input level of the IF signal is constant, there is an input level of the LO signal at which the output level of the RF signal becomes maximum.
Therefore, considering only the conversion gain of the mixer, it is preferable to use near the input level of the LO signal at which the output level of the RF signal is maximum. However, at the operating point where the output level of the RF signal is the maximum, the distortion rate does not reach the optimum value.
L higher than the operating point where the output level of the RF signal is maximum
It is better to set to the input level of the O signal.

Here, the input level of the LO signal input to the harmonic mixers 4 and 5 is
Are set so that the input level of the LO signal input to the harmonic mixer 5 is lower than the input level of the LO signal input to. For example, assume that the level input to the harmonic mixer 4 is “P1” and the level input to the harmonic mixer 5 is “P2”. If the harmonic mixer 4 and the harmonic mixer 5, and the detection circuit 6 and the detection circuit 7 have the same conversion and detection characteristics, as shown in FIG. 3, detection according to the two input levels of the LO signal on the same characteristic curve. The output is obtained.

The control circuit 8 detects the potential difference between the detection voltages output from the detection circuits 6 and 7, and controls the detection voltages corresponding to the input levels "P1" and "P2" of the LO signal to be equal. A voltage is output to control the amount of attenuation of the variable attenuator 1. By this control, as shown in FIG. 3, a stable state is reached in which the detection voltages are equal with respect to the detection voltage maximum point.

As described above, the input level “P” of the LO signal
By appropriately selecting the difference “P1−P2” between “1” and “P2”, that is, the power distribution ratio of the distributor 3, as shown in FIG. 2, the optimum LO signal is obtained from the conversion efficiency and distortion factor of the mixer. The input level “P1” can be automatically controlled as the input level of the harmonic mixer 4 for signal transmission.

Therefore, the conversion efficiency and the distortion rate of the harmonic mixer can be automatically controlled to the optimum operating point, and it is not necessary to use the buffer amplifier in a state where the output level is saturated. Therefore, there is an advantage that it is possible to prevent an output fluctuation due to the above and a decrease in reliability due to an excessive input to the buffer amplifier.

[0030]

As described above, according to the mixer operating point automatic control method and the frequency conversion circuit using the same according to the present invention, the level of the input local oscillation frequency signal can be reduced by using two mixers. By setting different levels and making the difference between the detection voltages of the two mixers equal, there is an effect that the mixer operating point can be automatically controlled to the optimum level.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of a frequency conversion circuit of the present invention.

FIG. 2 is a characteristic diagram showing an output level and a distortion rate of an RF signal with respect to an input level of an LO signal of a harmonic mixer.

FIG. 3 is a characteristic diagram illustrating a detection voltage output of a detection circuit with respect to an input level of an LO signal.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Variable attenuator 2 Buffer amplifier 3 Distributor 4, 5 Harmonic mixer 6, 7 Detection circuit 8 Control circuit

Claims (8)

[Claims] 1. An input signal having the same level and a local oscillation frequency signal having a different level are input to a first mixer and a second mixer, respectively, and the first mixer and the second mixer are input to the first mixer and the second mixer.
The output signals of the mixers are respectively detected, and a control signal corresponding to the detected voltage difference is generated, and the control signal is input to the first mixer and the second mixer so that the detected voltage difference becomes equal. An automatic control method of a mixer operating point, wherein a level of a local oscillation frequency signal is controlled equally. 2. An input signal of an intermediate frequency of the same level and a local oscillation frequency signal of a different level are input to a first harmonic mixer and a second harmonic mixer, respectively, and the first harmonic mixer and the second harmonic mixer are input to the first harmonic mixer and the second harmonic mixer. 2 and outputs a control signal corresponding to the difference between the detected voltages. An automatic control method of a mixer operating point, wherein the level of the input local oscillation frequency signal is controlled equally. 3. An amplifying means for amplifying an input local oscillation frequency signal, a distribution means for dividing the output of the amplifying means into two, and a first means for inputting an intermediate frequency signal having the same level as the two branched signals. , Second mixer means, first and second detection means for detecting the outputs of the first and second mixer means, respectively, and detecting a difference between detection voltages of the outputs of the first and second detection means. And a level control means for outputting a control signal for controlling an output level of the amplifying means so that the difference between the detection voltages becomes equal. 4. The amplifier according to claim 3, wherein said amplifying means comprises a variable attenuator for attenuating said local oscillation frequency signal and a buffer amplifier having a predetermined gain.
The described frequency conversion circuit. 5. The frequency conversion circuit according to claim 3, wherein the distribution unit has a level difference between the levels of the two branched signals, which is set in advance. 6. The frequency conversion circuit according to claim 3, wherein said first and second mixer means are harmonic mixers. 7. The first mixer means according to claim 3, wherein said local oscillation frequency signal having a higher level is inputted and an output signal is taken out.
The described frequency conversion circuit. 8. The second mixer means, wherein the local oscillation frequency signal of a lower level is input and the output side is terminated.
The described frequency conversion circuit.