JPH0570964B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a mixer circuit that receives a high frequency signal and a local oscillation signal and outputs a low frequency intermediate frequency signal.

[Prior art]

Direct TV broadcasting from geostationary satellites using 12GHz radio waves in the SHF band is planned in many countries around the world. FIG. 1 shows the configuration of a conventional general satellite broadcasting receiver. The satellite receiver includes an antenna 1, an outdoor converter 2, and an indoor receiving unit 3. Now, the 11.7 to 12.2 GHz television signal received by the antenna 1 is amplified by the preamplifier 4 of the outdoor converter 2, and converted into a first intermediate frequency signal in the 1 GHz band by the first mixer circuit 5. When the oscillation wave of the first oscillator 6 injected into the first Misaku circuit 5 is set to 10.8GHz,
The first intermediate frequency signal is a 0.9~1.4GHz signal,
The intermediate frequency amplifier 7 amplifies and outputs the signal. The first intermediate frequency signal is transmitted via cable 8 to indoor receiving unit 3. The indoor receiving unit 3 mainly includes an intermediate frequency converter 9, an FM demodulator 10, a video processing section 11, an audio demodulating section 12, a remodulator 13, and a tuning section 1.
4 and an AFC circuit 15. The intermediate frequency converter 9 includes an amplifier circuit 16 and a tuning filter 1.
7, second mixer circuit 18, second oscillator 19,
Consisting of a bandpass filter 20, the first intermediate frequency signal input from the cable 8 is amplified, the tuning filter 17 removes interference waves in unnecessary bands, and the second mixer circuit 18 amplifies the first intermediate frequency signal input from the cable 8. The signal is converted into a signal, and a bandpass filter 20 selects and outputs only the desired channel signal. Therefore, the second oscillator 19 is a variable frequency oscillator, and when the second intermediate frequency is set to 130 MHz, it generates a frequency 130 MHz higher than the first intermediate frequency signal in accordance with the tuning voltage from the tuning section 14. This second intermediate frequency signal is demodulated into a baseband signal by an FM demodulator 10 and separated into an audio carrier and a video signal.The video signal is subjected to waveform shaping such as de-enhancement in a video processing unit 11 and is output. . Further, the audio carrier is demodulated by the audio demodulation section 12 and output. Furthermore, the output video signal and audio signal are sent to a re-modulator 13.
Modulates and outputs VHF or UHF signals.
The FM demodulator 10 detects frequency detuning from the DC detection voltage of the FM detection, generates a control voltage in the AFC circuit 15, superimposes it on the tuning voltage, and controls the oscillation frequency of the variable oscillator 19 to be constant. do. Thus, the satellite broadcast receiver uses a double heterodyne receiver configuration consisting of an outdoor converter 2 with a first local oscillator 6 of fixed frequency and an intermediate frequency converter 9 with a second local oscillator 19 of variable frequency. .

The problem with the above configured receiver is the BC Engineering Report 5 of the June 1977 issue.
As shown in page Figure 7, this is the case when different signal bands are received. According to the above literature, 11.7
~12.1GHz and 12.1~12.5GHz satellite broadcasting is planned, and as shown in Figure 2, outdoor converter 21 and 12.1~12.5 will be installed to convert 11.7~12.1GHz signals to 0.9~1.3GHz intermediate frequency signals. This method uses an indoor receiving unit 23 in common with an outdoor converter 22 that converts a GHz signal into the above-mentioned intermediate frequency signal. This has the disadvantage that two types of outdoor converters are required depending on the region or desired reception band.

Naturally, it would be more convenient if one set of outdoor converter and indoor unit could be used for both of the different bands. This includes an outdoor converter that converts a 11.7~12.5GHz signal to 0.9~17GHz and a 0.9~17GHz signal.
An indoor receiving unit that receives a 17GHz intermediate wave signal is required, but in this case, the outdoor converter's received signal bandwidth is ±3.3% of 12.1GHz ± 0.4GHz, while the indoor receiving unit's received signal bandwidth is ±3.3% of 12.1GHz ± 0.4GHz. teeth
Wide range of 1.3GHz±30% of 0.4GHz. For this reason, the second mixer 18 of the intermediate frequency converter 9 shown in FIG. 1 is required to have wideband characteristics in order to convert high frequency signals of 0.9 to 1.7 GHz (800 MHz), resulting in the following drawbacks. .

Figure 3 shows a mixer circuit using a general 1/2 wavelength line. In this circuit, a diode 25 and two
6 in series in the same direction, 1/2 wavelength line 24
A local oscillation signal input line 28 (28A and 28B) having a capacitive circuit 27 is connected to one end, and a trap circuit 30 with a substantially short-circuit impedance is connected to the connection point of the diodes 25 and 26 with a low (intermediate) frequency signal.
Connect the high frequency signal input line 29 with the line 2
4 is connected to an intermediate frequency signal output line 31 having an impedance that is almost open to high frequency signals and local oscillation signals. The local oscillation signal input from the local oscillation signal input line 28 is transmitted through the diode 2 because the line 24 has a length of 1/2 wavelength.
The two diodes 5 and 26 are added in opposite phases and cancel each other out, so that the connection point between the diodes 25 and 26 is short-circuited. Diodes 25 and 2 like this
Since the high frequency signal input line 29 is connected to the connection point 6, the local oscillation signal is not excited (leaked) to the high frequency signal input line 29.

On the other hand, the high frequency signal input from the high frequency signal input line 29 is applied to the diodes 25 and 26 in the same phase. The connection point is short-circuited. the result,
The local oscillation signals are efficiently applied to the diodes 25 and 26 in opposite phases, and the high frequency signals are applied in the same phase.
Since the diodes 25 and 26 are oriented in the same direction, a low-frequency intermediate frequency signal having a frequency equal to the difference between the local oscillation signal and the high-frequency signal is output from the diodes 25 and 26 and is in phase with the line 24. Occurs in On the other hand, the connection point between the diodes 25 and 26 is connected to a trap circuit 30 provided on the high frequency signal input line 29.
This creates a short-circuit impedance for low-frequency signals, and the local oscillation signal input line 2
Since 9 is a capacitive circuit 27 and has an open impedance for low frequency signals, the intermediate frequency signals generated by the diodes 25 and 26 are combined on the line 24 and sent through the intermediate frequency signal output line 31. Output. This intermediate frequency output line 31 is
In order not to disturb the operation of the local oscillation signal and the high-frequency signal, the line 24 is passed through a low-pass filter 32 with an open impedance for these two signals.
connected to.

This mixer circuit has a band characteristic of approximately ±20% relative to the center frequency, which is wider than branch line balanced mixers and rattrace balanced mixers that use a 3dB divider, and is small and has a wide band. For satellite broadcasting in the range of 11.7 to 12.2 GHz, the first intermediate wave signal is 0.9 to 1.4 GHz, that is, 1.15 GHz±22%, which is wider than the band characteristic of the mixer circuit 18, but it has been confirmed through experiments that it can be used without problems. However, in 11.7 to 12.5 GHz satellite broadcasting, the first intermediate frequency signal is 0.9 to 1.7 GHz.
Since the frequency is as high as 1.3 GHz±30%, the bandwidth of the mixer circuit 18 is insufficient.

For this reason, there is a method of using a plurality of mixer circuits with different center frequencies. FIG. 4 shows a configuration example of an intermediate frequency converter 9 using two mixer circuits with different center frequencies. The mixer circuits 18a and 18b have different center frequencies, and the mixer circuits 18a and 18b have different center frequencies.
The first intermediate wave signal from the tuning filter 17, the local oscillation signal from the second oscillator 19, and the second intermediate wave signal output from the mixer circuits 18a and 18b are inputted to the interlocking switches 33 and 34. The configuration is such that either the mixer circuits 18a or 18b is operated. Here, the mixer circuit 18a
is carried with its center frequency at 1.1GHz, and the first intermediate frequency signal is carried at 0.9~1.3GHz, or 11.7~
Operates during 12.1GHz satellite broadcasting, mixer circuit 18
b has its center frequency signal carried at 1.5GHz,
The first intermediate frequency signal is 1.3~1.7GHz or 12.1
Operates during ~12.5GHz satellite broadcasting. As a result,
Since the mixer circuits 18a and 18b operate within the band of the mixer circuits 18a and 18b, which is within ±18% of the center frequency, good characteristics can be obtained.
However, in the above configuration, since a plurality of mixer circuits are required, the mixer circuits 18a, 18
The compact feature of the mixer constructed from the 1/2 wavelength line used in section b is lost, the shape of the intermediate frequency converter 9 becomes large, and the interlocking switch 3 is required to switch between the mixer circuits 18a and 18b.
3 and 34 are required, and its characteristic is that a large number of terminals are switched, and a device with low high frequency loss is required, making it expensive and complicated.

In addition, it is generally difficult to obtain the 800MHz oscillation band of 1.03 to 1.83GHz of the local oscillation signal required in the above example with a single second oscillator 19, so it is necessary to use two or more second oscillators. In the conventional method, multiple mixer circuits and a second oscillator must be switched, which increases the circuit scale.
There are drawbacks that make it even more complicated.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a mixer circuit which eliminates the above-mentioned conventional drawbacks, has a simple configuration, and can obtain good characteristics over a wide signal band.

[Summary of the invention]

In order to achieve the above object, the present invention provides a plurality of local oscillation signal input terminals on the 1/2 wavelength line constituting the mixer circuit according to the signal band to be used, and inputs the local oscillation signal according to the band to be used. By switching the input terminal, one mixer circuit can obtain good characteristics even in a wide signal band.

[Embodiments of the invention]

Hereinafter, the present invention will be explained in detail according to embodiments shown in the drawings. FIG. 5 is an operational principle diagram explaining the operation of the present invention. Conventionally, both ends of the 1/2 wavelength line 24 are connected and a high frequency signal is input to the midpoint A, and a local oscillation signal is input to one end B of the 1/2 wavelength line 24, but at this time, the 1/2 wave from B to B' The line length 35 of the wavelength line 24 is approximately 1/2 wavelength of the high frequency signal and local oscillation signal used, and the middle point A in the used band.
As mentioned above, and B are almost in a short-circuit state, but if C, which is inside one end B of the 1/2 wavelength line 24, is selected as the force of the local oscillation signal, the midpoints A and C are almost in a short-circuit state. The frequency is C', where C' is a distance equal to the length from B to C from the other end B' of the 1/2 wavelength line 24.
This is the frequency at which the line length 36 from C' to C' is a 1/2 wavelength, which means that the 1/2 wavelength line 24 is equivalently shortened and the operating band is moved upward. This is C
When is the input point of the local oscillation signal, the phase length from A to C via B is equal to the phase length from A to B' to C', and the local oscillation signal and This is because the phase changes of the high frequency signals are the same and are not directly involved in the operation of the mixer circuit. Here, the line length of the mixer circuit of the present invention and the input position of the local oscillation signal are determined as follows. The center frequency of the first operating band of the mixer circuit is f ₁ The center frequency of the second operating band is f ₂
(However, f ₁ < f ₂ ), the wavelength short circuit rate of the line used for the 1/2 wavelength line 24 is η, and the speed of light is D, the line length l ₁ of the 1/2 wavelength line 24 has two operations. Determined by the lower center frequency f ₁ in the band, approximately l ₁ =
Dη/2f ₁ , and at this time, the line length l ₂ of the 1/2 wavelength line 24 required for the second operating band is approximately l ₂ = Dη/2f ₂ , so the input position of the first local oscillation signal is The distance l between one end B of the 1/2 wavelength line 24 and the input position C of the second local oscillation signal may be selected to be approximately l=l ₁ -l ₂ /2. The above discussion assumes that one end B of the 1/2 wavelength line 24 is used as the input for the first local oscillation signal, and that C, which is separated from B by l determined by the above formula, is used as the input for the second local oscillation signal. However, it is clear that C', which is separated by l from the other end B' of the 1/2 wavelength line 24, can also be used as the input for the second local oscillation signal.

For these reasons, one mixer can have multiple operating bands by changing the input position of the local oscillation signal to the 1/2 wavelength line in the mixer circuit.

FIG. 6 shows an embodiment of the present invention, in which a local oscillation signal input line 28 and a 1/2
A local oscillation signal input line 38 having a capacitive circuit 37 exhibiting an open impedance in the intermediate frequency signal is provided at a distance determined by the above formula from the wavelength line and the connection point, and the second oscillator 19 A switch 39 switches the local oscillation signal from the oscillator. Considering the mixer circuit having a band of 0.9 to 1.7 GHz necessary for reception of satellite broadcasting of 11.7 to 12.5 GHz as described in the conventional example in the above embodiment, the line length of the 1/2 wavelength line 24 is 0.9 to 1.3 GHz. center frequency
The local oscillation signal input line 38 is connected to a center frequency of 1.5 GHz with an equivalent length of 1.3 to 1.7 GHz in the 1/2 wavelength line 24.
approximately 18 mm from the local oscillation signal input line 28 (however, the wavelength shortening rate η =
1, and the influence of the line width of the local oscillation signal input line is not considered)). Therefore,
Even when receiving satellite broadcasts from 11.7 to 12.5 GHz,
When receiving 11.7 to 12.1 GHz, the local oscillation signal output of the second oscillator 19 is applied to the local oscillation input line 28 by the switch 39, and when receiving 12.1 to 12.5 GHz, the local oscillation signal output of the second oscillator 19 is applied to the local oscillation input line 28. By applying the signal to the local oscillation input line 38 via the switch 39, good characteristics can be obtained with one mixer circuit. FIG. 7 shows another embodiment of the conventional 1/
A capacitive circuit 2 connected to one end of a two-wavelength line 24 and exhibiting open impedance in the intermediate frequency signal
7 and a local oscillation signal input line 28 having a capacitive circuit 40 exhibiting an open impedance in the intermediate frequency signal at a distance determined by the above formula from the other end of the 1/2 wavelength line 24. Two second oscillators 19A, 1 which are connected to the oscillation signal input line 41 and have different oscillation frequency bands.
The local oscillation signal from 9B is connected to the interlocking switch 42A,
42B and input it, interlocking switch 4
2A, 42B are two second oscillators 19A, 19
By interlocking with and switching the B +B power switches 43A and 43B, the same effects as in the former embodiment can be obtained with one mixer circuit. In particular, this embodiment is effective when the oscillation frequency band of one second oscillator is not sufficient and multiple second oscillators are required, and the second oscillators are placed on both sides of the mixer circuit. It also shows good results in terms of circuit configuration due to its placement. In addition, interlocking switches 42A, 42B
does not have to be a mechanical switch. FIG. 8 shows an example of an electronic switch, in which the local oscillation signal obtained from the collector of the output transistor 44 of the second oscillator 19 is input to a pin diode (or switching diode) 45, The output of the switching diode 45 is grounded through a resistor 46 and connected to a local oscillation signal input line 47 having a capacitive circuit 47 of the mixer circuit. The pin diode (or switching diode) 45 is
When a bias is applied in the forward direction and a current flows, the internal resistance decreases and the transistor becomes conductive. Therefore, when the second oscillator 19 is in operation, a forward bias is applied to the pin diode (or switching diode) 45 by the resistors 48 and 46, and the second oscillator 19 becomes conductive. The generated local oscillation signal is input to the mixer circuit, but when the +B power supply of the second oscillator 19 is cut off and its operation is stopped, no bias is applied to the pin diode (switching diode) 45, resulting in a high impedance. Therefore, the second oscillator 19 is disconnected, and the influence of the second oscillator 19 on the mixer circuit disappears.

Furthermore, in this embodiment, there are two local oscillation signal input lines.
Although the case is not limited to this, two or more local oscillation signal input lines are connected to appropriate positions on the 1/2 wavelength line, and the local oscillation signal is input according to the signal band to be used. By switching the mixer, good characteristics can be obtained in a continuous wide signal band or even in separate signal bands.

〔Effect of the invention〕

As described above, in the present invention, a plurality of local oscillation signal input terminals are provided on the 1/2 wavelength line constituting the mixer circuit according to the signal band to be used, and a terminal for inputting the local oscillation signal is provided depending on the band to be used. By switching, good characteristics can be obtained even in a wide signal band with one mixer circuit.

[Brief explanation of drawings]

Figure 1 is a block diagram showing the configuration of a conventional general satellite broadcasting receiver, Figure 2 is a block diagram showing the configuration for receiving different conventional signal bands, and Figure 3 is a block diagram of a conventional mixer circuit. Circuit diagram: Figure 4 is a block diagram showing the configuration of a conventional intermediate frequency converter;
FIG. 5 is a diagram of the operating principle of the present invention, FIGS. 6 and 7 are circuit diagrams of an embodiment of the present invention, and FIG. 8 is a circuit diagram of a switch circuit. 27, 37, 40, 47...capacitance circuit, 19...
...Second oscillator, 29...High frequency signal input line,
25, 26...diode, 28, 38, 41,
47... Local oscillation signal input line, 30... Trap circuit, 32... Low pass filter, 31... Intermediate frequency signal output line, 39, 43... Switch,
42... Interlocking switch, 44... Output transistor, 45... Pin diode (or switching diode), 46, 48... Resistor.

Claims (1)

[Claims] 1. A 1/2 wavelength line with a length of approximately 1/2 wavelength of the high frequency signal and local oscillation signal, a pair of diodes connected in series between both ends of the 1/2 wavelength line, and a a first line connected to one end, a circuit connected at or near the connection point of the first line and the 1/2 wavelength line and having high impedance to the intermediate frequency signal, and a pair of diodes. the second line connected to the connection point of and any one of the 1/2 wavelength lines
an intermediate frequency output line that is connected to a point and has an impedance that is almost open to local oscillation signals and high-frequency signals; and a circuit that is connected in parallel with the second line and has a low impedance to intermediate frequency signals. In a mixer circuit that inputs a local oscillation signal to the first line and a high frequency signal to the second line, the position of the 1/2 wavelength line excluding the connection point between the first line and the 1/2 wavelength line In addition, a third line or third
A circuit to which a plurality of lines from to nth are connected and which has a high impedance to an intermediate frequency signal at or near a connection point between a third line or a plurality of lines from third to nth and a 1/2 wavelength line. 1. A mixer circuit comprising: selectively supplying a local oscillation signal to a first line and a third line or a plurality of third to n-th lines according to a high-frequency signal band used.