JP2988277B2 - Image suppression mixer circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image suppression mixer circuit and, more particularly, to an image suppression mixer circuit for performing frequency conversion of a transmitted / received high-frequency signal.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram showing an example of a conventional image suppression mixer circuit. This image suppression mixer circuit (I
RM) is a high frequency (RF) signal input terminal (RF terminal)
1, RF hybrid 2 in RF frequency band, single mixer 3
a and 3b, local oscillation (LO) frequency input terminals (LO
Terminal) 4, an LO divider 5 for distributing the LO frequency into two, a 90 ° phase shifter 6 for shifting the intermediate frequency (IF) signal by 90 °, an IF combiner 7 for combining two signals in the IF frequency band, and An IF frequency output terminal (IF terminal) 8 is provided.

Next, the operation of the conventional circuit having the above configuration will be described. The RF signal input to the RF terminal 1 is divided by the RF hybrid 2 into two signals having the same amplitude and the phases shifted from each other by 90 °, and the single mixers 3a, 3b
Respectively. On the other hand, the LO frequency input to the LO terminal 4 has the same amplitude by the LO distributor 5, and
The phase is divided into two signals having the same phase, and a single mixer 3
a and 3b.

The single mixers 3a and 3b receive these input RF signals.
The frequency conversion between the signal and the LO signal is performed, and signals having the same amplitude and a 90 ° phase difference are output in the IF frequency band. The first I output from the single mixer 3a
The F signal is supplied directly to the IF synthesizer 7. On the other hand, the IF signal output from the single mixer 3b is
After being phase-shifted by 90 ° to be a second IF signal, it is supplied to the IF synthesizer 7.

[0005] An IF combiner 7 combines the first and second IF signals and outputs the combined signal to an IF terminal 8. Here, the first and second
Since the desired waves in the IF signals have the same amplitude and the same phase, their combined signals are output to the IF terminal 8.
However, since the image signal shifted from the LO signal by the IF frequency on the opposite side to the desired signal has the same amplitude and opposite phase in the first and second IF signals, the image signal is synthesized by the IF synthesizer 7. Is countered. Therefore, an IF signal in which the image signal is suppressed is output to the IF terminal 8.

Conventionally, a 90 ° hybrid circuit is used instead of the above 90 ° phase shifter 6, or RF
A mixer circuit having a configuration in which a 0 ° hybrid in the RF band is used as the hybrid 2, a 90 ° hybrid in the LO band instead of the LO distributor 5, and a 90 ° hybrid in the IF band instead of the IF combiner 7 is also known. However, these mixer circuits also suppress the image signal based on the same principle as described above.

[0007]

However, in the above-described conventional image suppression mixer circuit, the phase balance of the RF hybrid 2 and the LO distributor 5, the single mixers 3a and 3
Since the first and second IF signals input to the IF combiner 7 have a phase error due to the element variation of b, the phase shift error of the 90 ° phase shifter 6, and the like, the first and second IF signals are combined by the IF combiner 7. There is a problem that the image suppression ratio of the IF signal to be obtained cannot be sufficiently obtained, or the frequency band in which the image suppression ratio can be sufficiently obtained cannot be widened because it is limited by the frequency characteristics of the RF hybrid 2 or the like.

[0008] The present invention has been made in view of the above points,
Correct the degradation of the image suppression ratio due to the phase error of the element,
It is another object of the present invention to provide an image suppression mixer circuit capable of obtaining a sufficient image suppression ratio over a wide band by compensating for the frequency characteristics of elements.

[0009]

According to the present invention, in order to achieve the above object, an input high-frequency signal divided into two is divided into first and second input high-frequency signals.
Are converted into two intermediate frequency signals having the same amplitude and a different phase by 90 °, and one of them is converted into a first intermediate frequency signal to the first input terminal of the synthesizer. The other is supplied to the second input terminal of the synthesizer to be phase-shifted by -90 ° by the 90 ° phase shifter and supplied to the second input terminal of the synthesizer to synthesize the respective signals. In an image suppression mixer circuit for outputting a signal from a combiner, a first or second
A variable phase shifter that shifts the phase of the intermediate frequency signal by a phase amount according to the control signal and outputs the resultant to the first or second input terminal of the synthesizer, and the input intermediate frequency of the first input terminal of the synthesizer. A first coupler for branching a part of the signal, a second coupler for branching a part of an input intermediate frequency signal of a second input terminal of the combiner, and an intermediate branch branched by the first or second coupler. A third coupler for further branching a part of the frequency signal;
The first and second intermediate frequency signals extracted from the first and second couplers are frequency-converted with the intermediate frequency signals extracted by the third coupler, respectively, to thereby convert the first and second intermediate frequency signals. The first level corresponding to the phase of the signal
And a phase detecting means for converting the first and second DC signals output from the phase detecting means into a second DC signal. A configuration that includes a comparator that outputs an error signal, a control circuit that generates a control signal in accordance with the error signal, supplies the control signal to the variable phase shifter, and controls the amount of phase shift so that the phase difference becomes zero. It was done.

[0010]

According to the present invention, the first and second signals input to the synthesizer are provided.
The phase difference of the intermediate frequency signal is calculated by the above-described phase detection means and the comparator, and a control signal is generated by a drive circuit in accordance with the error signal indicating the phase difference and supplied to the variable phase shifter.
Since the amount of phase shift is controlled so as to make the above-mentioned phase difference zero, the input high-frequency signal is divided into two, and further frequency-converted by the first and second local oscillation frequencies, so that the amplitudes are equal to each other. In addition, the relative phase error between the first and second intermediate frequency signals caused by the phase balance and element balance of each circuit unit that converts the signals into two intermediate frequency signals having phases different by 90 °, the phase error of the 90 ° phase shifter, and the like. Can be corrected.

[0011]

Next, an embodiment of the present invention will be described. FIG. 1 shows a configuration diagram of an embodiment of the present invention. In the figure, the same components as those in FIG. 4 are denoted by the same reference numerals. In FIG. 1, the present embodiment further includes a variable phase shifter 10, couplers 11a, 11b and 11c, amplifiers 12a and 12
b and 12c, single mixers 13a and 13b, IF distributor 14, comparator 15, and drive circuit 16.

The variable phase shifter 10 shifts the phase of the output signal of the single mixer 3a in accordance with the control signal from the drive circuit 16. The couplers 11a and 11b respectively branch and extract a part of each output signal of the variable phase shifter 10 and the 90 ° phase shifter 6 input to the IF combiner 7. Coupler 11
“c” further branches the output signal of the 90 ° phase shifter 6 branched by the coupler 11b. Amplifiers 12a, 12b and 12c are coupled to couplers 11a, 11b and 11 respectively.
The signal c is amplified by c to the power required to operate in the saturation region.

The single mixers 13a and 13b are connected to the amplifier 1
The frequency conversion between the output signals of the amplifiers 12a and 12b and the output signal of the amplifier 12c divided into two by the IF distributor 14 is performed. The comparator 15 calculates a phase difference between the output signals of the single mixers 13a and 13c. The driving circuit 16 includes a comparator 15
Is applied to the variable phase shifter 10 as a control signal.

Here, the coupler 11a to the amplifier 12
a, coupler 11b to amplifier 12b, coupler 1
The respective phases of 1c to amplifier 12c, amplifier 12a to single mixer 13a, amplifier 12b to single mixer 13b, amplifier 12c to IF distributor 14, and IF distributor 14 to single mixers 13a and 13b are matched. .

Next, the operation of this embodiment having the above configuration will be described. The RF signal input from the RF terminal 1 is R
After being divided by the F hybrid 2 into two signals having the same amplitude and a phase difference of 90 °, the single mixer 3a,
3b, the LO signal from the LO terminal 4 is frequency-converted by the LO distributor 5 into a LO signal divided into two equal amplitudes and the same phase, and converted into an IF signal.

The first I extracted from the single mixer 3a
The F signal is a signal in which the desired wave and the image signal shifted from the LO signal by the IF frequency to the opposite side to the desired signal are equal in amplitude and differ in phase by 90 °, and are provided to improve the image suppression ratio. The IF signal is supplied to the IF synthesizer 7 through the variable phase shifter 10 and the coupler 11a. Also, a single mixer 3
In the IF signal extracted from b, the desired signal and the image signal shifted from the LO signal by the IF frequency on the opposite side to the desired signal have the same amplitude, the phases are shifted from each other by 180 °, and ° phase shifter 6 where it is phase-shifted by -90 ° relative to the first IF signal to produce a second I
After being converted into the F signal, the signal is supplied to the IF synthesizer 7 via the coupler 11b. These first and second IF signals are vector-combined by the IF combiner 7, so that the image signal is canceled and the IF converted from the desired wave is converted.
The signal is output to the IF terminal 8. The above operation is the same as that of the conventional circuit shown in FIG.

Further, in this embodiment, the following operation is performed in order to correct the phase difference between the first and second IF signals input to the IF synthesizer 7. That is, the first IF signal output from the variable phase shifter 10 is partly branched and taken out by the coupler 11a and amplified by the amplifier 12a to the power required to operate in the saturation region.
It is supplied to the single mixer 13a.

On the other hand, the second output from the 90 ° phase shifter 6
Part of the IF signal is extracted by the coupler 11b and taken out, amplified by the amplifier 12b to the power required to operate in the saturation region, and then amplified by the single mixer 13b.
Is further branched and extracted by the coupler 11c, amplified to the power required to operate in the saturation region by the amplifier 12c, and then supplied to the IF distributor 14. The IF distributor 14 receives the input second
Are divided into two and output to the single mixers 13a and 13b.

The single mixer 13a includes an amplifier 12a and an IF
The frequency conversion of each output IF signal of the distributor 14 is performed and a phase-detected DC signal is output. Also, the single mixer 13b
Converts the frequency of each output IF signal of the amplifier 12b and the IF distributor 14 and outputs a phase-detected DC signal.
Here, as described above, the phases of the signals input to the single mixers 13a and 13b are set to be equal to each other, and the amplitudes are amplified so as to be used in the saturation region. The difference between the level of the DC signal and the first and second IF
Appears as a signal phase difference.

FIG. 2 shows this relationship. In the figure, the vertical axis indicates the level difference of the DC signals (DC signals) output from the single mixers 13a and 13b, and the horizontal axis indicates the relative phase difference. Here, when a use frequency signal is input to the RF terminal 1 in advance, and the phase amount of the variable phase shifter 10 is varied from 0 ° to 360 ° to obtain the output voltage maximum value P (V), FIG. Such characteristics are obtained.

Accordingly, the phase amount φ to be corrected is obtained from FIG.

Φ = sin ^-1 {(DC signal difference) / P} (deg) The comparator 15 compares the levels of the DC signals output from the single mixers 13 a and 13 b, and An error signal corresponding to the phase difference between the first and second IF signals is generated (the phase difference is calculated from the DC signal difference). The drive circuit 16 receives this error signal from the comparator 15 as an input signal, generates a control signal that makes the phase amount φ in the above equation zero, and controls the phase amount of the variable phase shifter 10.

With the above operation, the RF hybrid 2,
Since a relative phase error caused by the phase balance of the LO distributor 5, the element variation of the single mixers 3a and 3b, the phase error of the 90 ° phase shifter 6, and the like can be corrected, a sufficient image suppression ratio can be obtained as compared with the related art. Obtainable.

In this embodiment, the single mixer 13a,
By obtaining the frequency characteristics of the maximum value of the output voltage of 13b, the frequency band limited by the hybrid circuit (that is, the RF hybrid 2, the LO distributor 5, and the like) can be widened.

It should be noted that the present invention is not limited to the above-described embodiment. For example, as shown in FIG.
0 may be provided on the 90 ° phase shifter 6 side. In the embodiment, the third coupler 11c branches the second IF signal branched from the second coupler 11b. However, the third coupler 11c is preferably based on the IF signal that does not pass through the variable phase shifter 10. This is because setting is easy, and in principle, the first IF signal branched by the first coupler 11a may be branched.

[0026]

As described above, according to the present invention,
The phase difference between the first and second intermediate frequency signals input to the synthesizer is calculated by the phase detection means and the comparator, and a control signal is generated by a drive circuit in accordance with the error signal indicating the phase difference. The input high frequency signal is divided into two by controlling the phase shift amount so as to make the above-mentioned phase difference zero by supplying the input high frequency signal to the variable phase shifter, and further performing frequency conversion by the first and second local oscillation frequencies, respectively. And the amplitudes are equal to each other, and
Corrects the relative phase error between the first and second intermediate frequency signals caused by the phase balance and element balance of each circuit unit that converts the signals into two intermediate frequency signals having different phases by 90 °, the phase error of the 90 ° phase shifter, and the like. Therefore, a sufficient image suppression ratio can be obtained as compared with the related art.

Also, according to the present invention, the frequency characteristic of the output voltage value of the first and second single mixers is determined in advance, so that the frequency band limited by the hybrid circuit or the like is wider than before. be able to.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a phase difference between two signals of a main part of FIG. 1;

FIG. 3 is a configuration diagram of another embodiment of the present invention.

FIG. 4 is a configuration diagram of a conventional example.

[Explanation of symbols]

Reference Signs List 1 RF terminal 2 RF hybrid 3a, 3b, 13a, 13b Single mixer 4 LO terminal 5 LO distributor 6 90 ° phase shifter 7 RF synthesizer 8 IF terminal 10 Variable phase shifter 11a, 11b, 11c First, second , Third coupler 12a, 12b, 12c first, second, third amplifier 14 IF distributor 15 comparator 16 drive circuit

Claims (2)

(57) [Claims] An input high-frequency signal divided into two is frequency-converted by first and second local oscillation frequencies, respectively, and converted into two intermediate-frequency signals having the same amplitude and a different phase by 90 °. Is supplied as a first intermediate frequency signal to a first input terminal of the combiner, and the other is phase-shifted by -90 ° by a 90 ° phase shifter to produce a second intermediate frequency signal at a second input of the combiner. In the image suppressing mixer circuit that outputs an intermediate frequency signal whose image has been suppressed from the combiner by supplying the signals to the terminals and combining them, the phase of the first or second intermediate frequency signal is adjusted according to a control signal. A variable phase shifter for phase-shifting the phase to output to the first or second input terminal of the synthesizer; and a first branching part of the input intermediate frequency signal of the first input terminal of the synthesizer. A coupler; and a second one of the combiners. A second coupler for branching a part of the input intermediate frequency signal of the input terminal of the first and second couplers; a third coupler for further branching a part of the intermediate frequency signal branched by the first or second coupler; The first and second intermediate frequency signals extracted from the first and second couplers are frequency-converted with the intermediate frequency signals extracted by the third coupler, respectively, to perform the first and second intermediate frequency signals. A phase detecting means for converting the first and second DC signals output from the phase detecting means into first and second DC signals having a level corresponding to the phase of the frequency signal; And a comparator that outputs an error signal corresponding to the phase difference between the second intermediate frequency signal and a control signal that is generated in accordance with the error signal and supplied to the variable phase shifter. Control to make the phase difference zero An image suppression mixer circuit comprising: a driving circuit. 2. The first and second phase detectors amplify respective intermediate frequency signals extracted from the first, second, and third couplers to electric power necessary for operating the respective intermediate frequency signals in a saturation region. A second and a third amplifier, a divider for dividing the output signal of the third amplifier into two, and a frequency conversion between the first amplifier and the output signal of the divider to convert the first DC signal. A first single mixer for outputting a signal, and a second single mixer for converting the frequency of the output signal of the second amplifier and the output signal of the distributor and outputting the second DC signal. The image suppression mixer circuit according to claim 1, wherein: