JPH0720023B2 - Frequency conversion circuit - Google Patents

Description

The present invention relates to a frequency conversion circuit used in, for example, a direct conversion receiver.

[Conventional technology]

The second example of the configuration of the direct conversion receiver
Shown in the figure.

This receiver is a high frequency signal RF input from the antenna etc.
Is supplied to the two mixers 6a and 6b via the high-frequency filter 2 and the high-frequency amplifier 4, while the local oscillation signal LO from the local oscillator 10 is supplied to the mixer 6a side via the π / 2 phase shifter 8. It is supplied to the mixer 6b side as it is, and each mixer 6a
It is configured to extract the intermediate frequency signals IF ₁ and IF ₂ from 6 and 6b, respectively, and supply them to the product detector 14 via the low-pass filters 12a and 12b, respectively, and perform product detection there to extract the audio signal AF. There is.

The frequency conversion circuit 5 surrounded by a broken line is configured using a double balanced mixer using a core-in transformer and a π / 2 phase shifter configured by LC at a frequency of several hundred MHz or less. In the microwave band over several GHz, a planar circuit is used, and a hybrid coupler (for example, branch line, rat race, etc.) is combined with two diodes and a λ / 4 length (λ is a high frequency signal dielectric substrate). (Wavelength above) with a π / 2 phase shifter.

When the latter is actually realized on a plane circuit, an example in which this is composed of two rat race mixers 16a, 16b, microstrip line delay lines 23a, 23b and two Wilkinson power splitters 24a, 24b is shown in FIG. Shown in.

Each rat race mixer 16a, 16b has two diodes 20a, 22a, 20b, 22b respectively connected to the positions of annular transmission lines (rat races) 18a, 18b as shown in the figure.

Further, the lengths L ₁ and L ₂ in the delay lines 23a and 23b have a relationship of L ₁ −L ₂ = λ / 4, which constitutes a π / 2 phase shifter.

[Problems to be Solved by the Invention]

However, the frequency conversion circuit shown in FIG. 3 requires two rat-race mixers 16a and 16b, two power splitters 24a and 24b, and a π / 2 phase shifter, which makes the configuration complicated. In addition, there is a problem that the lengths L ₁ and L ₂ for obtaining the phase difference of π / 2 in the delay lines 23a and 23b require high accuracy.

Therefore, it is a primary object of the present invention to improve the frequency conversion circuit configured by the above planar circuit and to simplify the circuit configuration.

[Outline of Invention]

In order to achieve the above object, the frequency conversion circuit of the present invention, roughly speaking, uses two rat race mixers with a λ / 4.
It is characterized in that the π / 2 phase shift on the local oscillation side is performed on the high frequency side by connecting to each other via a long transmission line, thereby omitting a special phase shifter and a power splitter used for distribution of high frequency signals. To do.

〔Example〕

FIG. 1 is a circuit diagram showing a frequency conversion circuit according to an embodiment of the present invention.

The frequency conversion circuit of this embodiment is provided on a dielectric substrate (not shown), and both are 3 / 2λ (λ
Is the wavelength of the input high frequency signal RF on the dielectric substrate)
The first and second annular transmission lines (rat races) 18a and 18b having the length of

For each of the annular transmission lines 18a and 18b, the first and second output terminals 32a, 33a and 33a are provided inside two positions b and c which are arbitrarily separated by λ / 4 from the position a in the opposite direction. 32b and 33b are provided, and in this example, the input terminal 34 for the local oscillation signal LO is located at a position d further λ / 4 away from the position b therein.
a and 34b are provided.

Such two ring-shaped transmission lines 18a and 18b are connected to each other through the transmission line 28 having a length of λ / 4 at the antipodal points e of the respective arbitrary positions a.

In this example, the input terminal 31a for the high frequency signal RF is provided at the arbitrary position a of the first annular transmission line 18a.

Further, for each annular transmission line 18a, 18b,
The first diodes 20a, 2 are connected to the first output terminals 32a, 32b.
The second output terminal 33 is connected to the anodes of 0b.
The cathodes of the second diodes 22a and 22b are connected to a and 33b, respectively, and the cathodes of the first diodes 20a and 20b and the anodes of the second diodes 22a and 22b are connected to each other with intermediate frequency signals IF ₁ and IF _{2 respectively.} Are connected to output terminals 35a and 35b, respectively.

Thus, the first and second rat race mixers
26a and 26b are constructed and connected to each other via a transmission line 28.

Then, the input terminal 34 of each rat race mixer 26a, 26b
In this example, a Wilkinson type power splitter 24 is connected to a and 34b, and local oscillation signals LO in phase with each other are input through the power splitter 24.

According to the above configuration, the high-frequency signal RF input to the input terminal 31a of the first rat race mixer 26a receives the antipodal point e thereof.
Then, the phase is delayed by 3 / 4λ (= 3 / 2π), and further λ / 4 (= π
It is supplied to the second rat race mixer 26b via a transmission line 28 having a length of / 2). Second rat race mixer 2
For 6b, this becomes a high frequency input, and the phase is delayed by 2π from the high frequency input of the first rat race mixer 26a. That is, there is no phase delay.

On the other hand, in the second rat race mixer 26b, the diodes 20b and 22b are connected to the first rat race mixer 26a at a position separated from the input point e of the high frequency signal RF by π (= λ / 2). The position of the diode is π / 2 different in comparison.
Therefore, compared to the first rat race mixer 26a,
In the rat race mixer 26b, the phase of the high frequency signal RF is delayed by π / 2.

Therefore, when the local oscillation signal LO from the power splitter 24 is input in phase to the input terminals 34a, 34b of both rat race mixers 26a, 26b, the phase between the high frequency signal RF and the local oscillation signal LO is the rat race mixer 26a side and rat race. It has the same function as the frequency conversion circuit 5 of FIG. 2 or the frequency conversion circuit of FIG. 3 in which the local oscillation signal LO is delayed by π / 2 and input to one side by π / 2 shift from the mixer 26b side.

Moreover, according to this frequency conversion circuit, unlike the example of FIG. 3, the π / 2 phase shifter on the local oscillation side can be omitted, and the power splitter used for distributing the high frequency signal RF can also be omitted. it can. Therefore, the circuit configuration is simplified and the cost can be reduced accordingly.

Further, since the planar circuit around the two annular transmission lines 18a and 18b can be formed line-symmetrically (symmetrically to the line A in FIG. 1),
There is also an effect that the design of the mask pattern for forming them becomes easy.

It is also possible to provide an input terminal at the position a of the second annular transmission line 18b and input the high frequency signal RF from here, and also to provide an input terminal at the position f of both annular transmission lines 18a and 18b. , Local oscillation signals LO in phase with each other may be input, and in either case, the same operation as in the example of FIG. 1 is performed.

If a high dielectric constant dielectric substrate is used as the substrate that constitutes the frequency conversion circuit, the diameters of the annular transmission lines 18a and 18b can be reduced, and the conventional double balanced mixer and LC can be used for π / 2 phase shift. It is possible to use the above-mentioned planar circuit even in the several hundred MHz band, which was configured by a container, which can significantly reduce the number of parts and the number of parts to be attached, resulting in a significant cost reduction.

〔The invention's effect〕

As described above, according to the present invention, the π / 2 phase shifter on the local oscillation side and the power splitter used for distributing the high frequency signal can be omitted, so that the circuit configuration is simplified and the cost is reduced accordingly. be able to. Further, since the plane circuits around the two annular transmission lines can be formed line-symmetrically, there is an effect that the design of the mask pattern for forming these becomes easy.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a frequency conversion circuit according to an embodiment of the present invention. FIG. 2 is a block diagram showing an example of a direct conversion receiver. FIG. 3 is a circuit diagram showing an example of a conventional frequency conversion circuit. 18a, 18b …… annular transmission line, 20a, 20b, 22a, 22b …… diode, 24 …… power splitter, 26a, 26b …… rat race mixer, 28 …… transmission line, 31a …… high frequency signal input terminal, 32a, 32b ... first output terminal, 33a, 33b ... second output terminal, 34a, 34b ... local oscillation signal input terminal, 3
5a, 35b ... Output terminal for intermediate frequency signal.

Claims (1)

[Claims] 1. A dielectric substrate, which is (3 /
2) First and second annular transmission lines having a length of λ (where λ is the wavelength on the dielectric substrate of the input high frequency signal) are provided, and for each annular transmission line, First at two positions separated from each other by λ / 4 in opposite directions
And a second output terminal are provided, and an input terminal for the local oscillation signal is provided at a position further λ / 4 away from either one of the two positions, and both ring-shaped transmission lines are provided with the above-mentioned arbitrary ones. The antipodal points with respect to the position are connected to each other via a transmission line having a length of λ / 4, and the high-frequency signal input terminal is provided at the arbitrary position of either one of the annular transmission lines. , For each ring transmission line,
The first output terminal is connected to the anode of the first diode, the second output terminal is connected to the cathode of the second diode, and the cathode of the first diode and the anode of the second diode are respectively connected. Is connected to the output terminal of the intermediate frequency signal, and the local oscillation signals of the same phase are input to the input terminals of the local oscillation signal of each annular transmission line.