JP2796360B2 - Transmission mixer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] A mixer used in a microwave radio apparatus is provided with a four-terminal 90 ° hybrid circuit for the purpose of suppressing an unnecessary wave output level due to a clock signal for modulation. One end of each of the two diodes is connected to two of the four terminals of the hybrid circuit, and the remaining two terminals are respectively configured as a first signal input terminal and a signal output terminal. In a mixer to which an input terminal is connected, the two diodes are connected in opposite directions, and a quarter-wave phase shifter is provided between one of the two diodes and the hybrid circuit. It is configured to interpose.

[Industrial applications]

The present invention relates to a mixer used for a microwave radio device.

In the transmitting section of the microwave radio device, an IF signal (for example, 70
MHz), and is mixed with a local signal in the microwave band and converted into a desired microwave band signal. A transmission mixer using a Schottky diode is used in this mixing unit. Further, as a modulation method of the IF signal, phase modulation (for example, 4-phase PSK), amplitude phase modulation (for example, 16QAM) and the like are used.

[Conventional technology]

2. Description of the Related Art Conventionally, as a transmission mixer used in a microwave radio apparatus, there is one shown in FIG. FIG. 6 is an equivalent circuit diagram showing the configuration of a conventional transmission mixer. In FIG. 6, 1 is a local signal input terminal, 2 is an RF signal (desired microwave band signal) output terminal, and 3 is an IF The signal input terminal 4 is a 90 ° hybrid circuit, and the hybrid circuit 4 has four terminals 4a to 4d.
The terminals 4a and 4b are connected to the local signal input terminal 1 and the RF signal output terminal 2 via DC cut capacitors 8 and 8, respectively, and are configured as a signal input terminal and a signal output terminal. On the other hand, Schottky diodes 5a and 5b are connected in the same direction to the remaining two terminals 4c and 4d, respectively, and the IF signal input terminal 3 is connected via a DC cut capacitor 8.

6 is a 1/4 wavelength open stub of the operating frequency, 7
Is a choke coil for the DC return of the diodes 5a, 5b.

IF signal input terminal 3 of the transmission mixer having such a configuration
FIG. 7A shows the spectrum of the RF output signal output from the RF signal output terminal 2 when an IF input signal (multi-level modulated) having the spectrum shown in FIG. It is shown in b). In FIG. 7B, reference numerals 21 and 22 denote spectrum portions of RF signals obtained by mixing IF signals having the spectrum shown in FIG. 7A with local signals in the above-described mixer hybrid circuit 4 and frequency-converting them. Frequency f _LO ±
f _IF ) and 23 indicate a spectrum portion (frequency f _LO ) in which the local signal from the input terminal 1 is wet to the RF signal output terminal 2 side.

[Problems to be solved by the invention]

By the way, as shown in FIG.
Although the signal at the clock frequency f _CL is not found in the spectrum of the signal, as shown in FIG. 7B, the spectrum of the RF output signal has a frequency that is ± f _CL away from the local frequency f _LO. The spectrum part 24 appears. This is an unnecessary signal, and in some cases, it approaches the spectrum part 21 or 22 corresponding to the required RF signal modulation wave, and cannot be sufficiently removed by the microwave band filter. It is difficult to get a good D / u.

The generation process of the unnecessary signal (spurious) will be briefly described. When a signal multi-level modulated at the clock signal frequency f _CL is input to a non-linear element such as a diode, a signal at the clock frequency f _CL is reproduced. In the conventional mixer shown in FIG. 6, the modulation signal (IF signal) input from the IF signal input terminal 3 is input to the diodes 5a and 5b in the same phase, and the signal of the clock frequency _fCL is reproduced. On the other hand, the local signal input to the input terminal 1 is applied to the diodes 5a and 5b with a 90 ° phase difference in the 90 ° hybrid circuit 4. The local signal and the reproduced clock signal are mixed, and a signal having a frequency f _LO ± f _{CL having} a phase difference of 0 ° or 180 ° is generated in the diodes 5a and 5b. , Appear at the RF signal output terminal 2 and become a signal corresponding to the spectrum part indicated by reference numeral 24 in FIG.

SUMMARY OF THE INVENTION An object of the present invention is to provide a mixer that solves such a problem and that can suppress an unnecessary wave output level due to a clock signal for modulation to be low.

[Means for solving the problem]

 FIG. 1 is a principle circuit diagram of the present invention.

In FIG. 1, 3 is an IF signal input terminal, 4 is a 90 ° hybrid circuit, and this hybrid circuit 4 has four terminals 4a to 4a.
4d, of which two terminals 4a and 4b are configured as a first signal input terminal and a signal output terminal, respectively, while the remaining two terminals 4c and 4d are connected to Schottky diodes 5A and 5A, respectively. One end of 5B is connected, and the second signal input terminal 3 is connected to the other end of these diodes 5A and 5B.

In the present invention, these two diodes 5A, 5A
B are connected in opposite directions, and a quarter-wave phase shifter 9 is interposed between one diode 5A and the terminal 4c of the hybrid circuit 4. This phase shifter 9 causes a phase delay of 1/4 wavelength with respect to the frequency of the local signal.

[Action]

With the above configuration, the IF signals from the second signal input terminal 3 input to the diodes 5A and 5B are in phase,
Each diode 5A, because 5B are opposite to each other, the signal of clock frequency f _CL reproduced by the diodes 5A and 5B are reversed-phase.

On the other hand, the local signal from the terminal 4a is branched into two with a phase difference of 90 ° by the 90 ° hybrid circuit 4, but the local signals input to the diodes 5A and 5B are in-phase by the quarter-wave phase shifter 9. Become a relationship.

Next, the clock frequency f reproduced by the diodes 5A and 5B
The signals of the frequency f _LO ± f _CL generated by mixing the signal of the _{CL and} the signal of the local frequency f _LO are opposite to each other in the diodes 5A and 5B, and the input local signals are in phase. Signal of the frequency f _LO ± f _CL generated by the diode 5A due to the reverse phase relationship of the recovered clock signal of
The signal of the frequency f _LO ± f _CL generated by the diode 5B has the same phase.

These signals are combined with the phase shifter 9 and the 90 ° hybrid circuit 4
And unnecessary waves do not appear in the RF signal output from the terminal 4b.

〔Example〕

 Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 2 is an equivalent circuit diagram showing a configuration of a transmission mixer as a first embodiment of the present invention, and FIG. 3 is a circuit diagram showing a specific circuit configuration using a microstrip line corresponding to FIG. is there. In these FIGS. 2 and 3, 1 is a roll signal input terminal, 2 is an RF signal output terminal, 3
Is an IF signal input terminal, and 4 is a branch line type 90 ° hybrid circuit. The hybrid circuit 4 has two terminals 4a and 4b.
Are connected to the local signal input terminal 1 and the RF signal output terminal 2 via the DC cut capacitor 8, respectively, and are configured as a first signal input terminal and a signal output terminal.

In this embodiment, the remaining two terminals 4c and 4d of the hybrid circuit 4 are connected to the Schottky diodes 5A and 5A, respectively.
One end of 5B is connected in the opposite direction, and a DC cut capacitor 8 is connected to the other end of Schottky diodes 5A and 5B.
To the IF signal input terminal 3.

9 is one diode 5A and the hybrid circuit 4
And a phase shifter 9 of 1/4 wavelength interposed between the terminal 4c and the phase shifter 9. This phase shifter 9 is configured as a 1/4 wavelength transmission line, and has a 1/4 wavelength relative to the frequency of the local signal. Is caused.

In the figure, 6 is a 1/4 wavelength open stub of the used frequency, 7a and 7b function as choke coils for DC return of the diodes 5A and 5B, and 7a is a microwave side.
1/4 wavelength short stub provided in the DC return path, 7
b is a lumped constant choke coil on the IF side. Further, the entire circuit of the mixer according to the present embodiment is constituted by microstrip lines on an alumina ceramic substrate.

With the configuration described above, the output level of the unnecessary wave is suppressed in principle in the same manner as described above with reference to FIG.

That is, the IF signals from the input terminal 3 input to the diodes 5A and 5B are in phase,
Are opposite to each other, the signals of the clock frequency f _CL reproduced by the diodes 5A and 5B have opposite phases, while 9
The local signal from the input terminal 1 is branched into two at a phase difference of 90 ° by the hybrid circuit 4, but the local signals input to the diodes 5A and 5B are in-phase by the quarter-wave phase shifter 9. become.

The clock frequency f reproduced by the diodes 5A and 5B
The signals of the frequency f _LO ± f _CL generated by mixing the signal of the _{CL and} the signal of the local frequency f _LO are opposite to each other in the diodes 5A and 5B, and the input local signals are in phase. Signal of the frequency f _LO ± f _CL generated by the diode 5A due to the reverse phase relationship of the recovered clock signal of
The signal of the frequency f _LO ± f _CL generated by the diode 5B has the same phase.

These signals are combined with the phase shifter 9 and the 90 ° hybrid circuit 4
And unnecessary waves do not appear ideally in the RF signal output from the output terminal 2.

The mixing operation between the IF frequency f _IF and the local frequency f _LO is the same as that of the conventional mixer. This is because the local signal input to one diode 5A has a 90 ° phase delay in the phase shifter 9 and the RF signal converted by the diode 5A has a 90 ° phase delay in the phase shifter 9.
The phase difference is 180 ° in total, but because the directions of the diodes 5A and 5B are opposite to each other, the state is the same as the same-direction connection as shown in FIG.

As described above, according to the transmission mixer of the present embodiment, the unnecessary wave output level due to the clock signal for modulation can be suppressed to a low level, and the mixer can be easily implemented by a single-sided planar circuit as in the related art. Can be realized.

Here, the specific effect of the mixer of this embodiment is shown in FIG. 4 in comparison with the conventional one. FIG. 4 shows a case where a branch line type designed at 8 GHz is used as the hybrid circuit 4 and a transmission line having a quarter wavelength at 8 GHz is used as the phase shifter 9. 7 (portion indicated by reference numeral 24 in FIG. 7B)] shows an actual measurement value measured at the output terminal 2. This fourth
As is apparent from the figure, the output level of the unnecessary wave from the mixer of the present embodiment is confirmed to be improved by 10 dB or more as compared with the conventional one.

Next, a transmission mixer as a second embodiment of the present invention will be described. FIG. 5 is a circuit diagram showing a specific circuit configuration. In FIG.
It is a matching circuit for matching A, 5B and 50Ω load,
Thereby, the impedance characteristics of the local signal input terminal 1 and the RF signal output terminal 2 are improved. In the second embodiment, the phase shifter 9 is interposed between the matching circuit 10 on the diode 5A side and the terminal 4c of the 90 ° hybrid circuit 4. Further, in the second embodiment, unlike the first embodiment, an inductor constituting a DC return path (see reference numerals 7a and 7b in FIGS. 2 and 3)
However, if there is no problem that the internal resistance of the diodes 5A and 5B becomes a bias resistance, a path through which a DC current flows is configured, so that the inductor can be omitted.

With the above-described configuration, the same operation and effect as those of the above-described first embodiment can be obtained in the second embodiment, and as described above,
The impedance characteristics of the local signal input terminal 1 and the RF signal output terminal 2 can be improved.

In the first and second embodiments described above, the case where the 90 ° hybrid circuit 4 is a branch line type is described, but other types such as an interdigital type may be used.

〔The invention's effect〕

As described in detail above, according to the mixer of the present invention, a 90 ° hybrid circuit having four terminals is provided. One end of each of two diodes is connected to two of the four terminals of the hybrid circuit, and the remaining two terminals are connected. Terminals are first
Assuming that a second input terminal is connected to the other end of each diode, two diodes connected to two of the four terminals of the 90 ° hybrid circuit are configured as a signal input terminal and a signal output terminal. In the opposite directions, and 1 /
With an extremely simple configuration in which a four-wavelength phase shifter is interposed, an effect that the unnecessary wave output level due to the clock signal for modulation can be reliably suppressed to a low level is obtained.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of the principle of the present invention, FIG. 2 is an equivalent circuit diagram showing a configuration of a transmission mixer as a first embodiment of the present invention, and FIG. 3 uses a microstrip line corresponding to FIG. FIG. 4 is a graph showing a comparison between the spurious wave output level of the mixer of the present embodiment and the spurious wave output level of the conventional mixer, and FIG. 5 is a circuit diagram of the present invention. FIG. 6 is a circuit diagram showing a specific circuit configuration of a transmission mixer as a second embodiment, FIG. 6 is an equivalent circuit diagram showing a configuration of a conventional transmission mixer, and FIGS. IF in equipment
5 is a graph showing an input signal spectrum and an RF output signal spectrum. In the figure, 1 is a local signal input terminal, 2 is an RF signal output terminal, 3 is an IF signal input terminal, 4 is a 90 ° hybrid circuit, 4a to 4d are terminals, 5A and 5B are Schottky diodes, and 6 is 1/4. Wavelength open stub, 7a is a short stub, 7b is a choke coil, 8 is a DC cut capacitor, 9 is a phase shifter, and 10 is a matching circuit.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H03D 7/00-7/04 H03D 7/14-7/18 H03D 9/06

Claims (1)

(57) [Claims] 1. A four-terminal 90 ° hybrid circuit,
One end of each of the two diodes is connected to two of the four terminals of the hybrid circuit, and the remaining two terminals are respectively configured as a first signal input terminal and a signal output terminal. In a mixer to which an input terminal is connected, the two diodes are connected in opposite directions, and a quarter-wave phase shifter is provided between one of the two diodes and the hybrid circuit. A mixer characterized in that a mixer is interposed.