JPH0311807A - Modulation and demodulation circuit - Google Patents

Abstract

PURPOSE:To reduce number of components by utilizing a phase difference between a symmetrical mode and an anti-symmetrical mode in a MODEM circuit using signals shifted by 90 deg.. CONSTITUTION:A reception high frequency signal is converted into 1st and 2nd high frequency signals having a phase difference of 90 deg. with a surface acoustic wave filter 23, the frequency is converted by mixers 24, 25 and the result is given to low pass filters 27, 28. The frequency decreased to a base band frequency is given to mixers 33, 34 and the resulting output is differentially amplified by a differential amplifier 35 and a demodulation output is obtained. Thus, the adjustment of the level difference between two signals and the phase difference is omitted.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a modulation/demodulation circuit that performs angle modulation or demodulation using two signals having a phase difference of 90°, and in particular,
This invention relates to a surface acoustic wave filter that uses a surface acoustic wave filter as a means for generating a phase difference of 0°.

[Conventional technology]

In recent years, wireless communication devices such as pagers and cordless telephones have become rapidly popular. In these wireless communication devices, angle modulation such as FM or PM is generally used as a modulation method in many cases.

Conventionally, superheterodyne type receiving circuits have been widely used as angle modulation type receiving circuits. Although the superheterodyne method achieves good reception characteristics, (a) it requires a relatively complicated circuit, and (b) it requires an expensive element such as a crystal filter as an intermediate frequency bandpass filter. Furthermore, (c) the intermediate frequency stage is
It had the disadvantage that it was difficult to convert it into an I. result,
It was difficult to make it smaller and lower in price.

On the other hand, a direct conversion type modulation/demodulation circuit is being considered as a system suitable for integrating up to the baseband portion into an LSI and capable of achieving reductions in size and cost. The circuit configuration of a receiver using an example of this circuit will be briefly described with reference to FIG.

The high frequency signal received by antenna 1 is transmitted to high frequency amplifier 2.
The signal is amplified by the high frequency bandpass filter 3 and filtered by the high frequency bandpass filter 3. The filtered high frequency signals are applied to mixers 4 and 5, respectively.

On the other hand, a carrier signal generated by a carrier wave oscillator 6 and filtered by a bandpass filter 7 is applied to one mixer 5 via a buffer amplifier 8. The output of the buffer amplifier 8 is also given to a 90'' phase shifter 9.
The signal is applied to the other mixer 4 via an amplifier 10.

The received signals immediately dropped into the Haasband by the mixer 4.5 are then passed through the low-pass filters 11 and 11, respectively.
given to. After the low-pass filters 11 and 12, amplifiers 13 and 14, differentiating circuits 15 and 16, and a mixer 1
7.18 are connected, and the output of the mixer 17.18 is amplified by the differential amplifier 19 to obtain a demodulated output.

In the above configuration, the intermediate frequency stage (amplifier, intermediate frequency filter, etc.) required for the superheterodyne method is not required, so the circuit section after the part shown by the broken line A, that is, the configuration after the baseband section, is made up of 1,000 mp. It can be configured as an LSI. Therefore, miniaturization and cost reduction can be achieved.

[Technical Problem to be Solved by the Invention] When a direct conversion method is adopted, the balance between two signal paths having a phase difference of 90° is very important.

This is because if there is a difference in signal level or a shift in phase difference between the two signal paths, the characteristics will deteriorate.

If the baseband part after the mixers 4 and 5 is implemented as an LSI, it will be realized with a monolithic structure, so that circuit balance and symmetry can be achieved with high precision.

However, the 901 phase shifter 9 connected to the carrier wave oscillation circuit 6 poses a problem. That is, the 906 phase shifter 9 is generally composed of about two stages of LC filters, but
In that case, a phase difference error tends to occur due to a drop in the signal level or variations in the values of L or C, and it is impossible to use the device unless level adjustment and phase difference adjustment are performed.

Furthermore, since the output of the carrier wave oscillation circuit 6 generally includes spurious signals, a tank circuit (bandpass filter) consisting of an LC is provided at the output. Because of mutual interference between the two, it was necessary to insert a buffer amplifier 8 between them. As a result, as mentioned above, a relatively complex circuit configuration is required.

An object of the present invention is to provide a modulation/demodulation circuit using a modulation method using carrier signals having a 90° phase difference, which eliminates the need for adjusting a 90° phase shifter and simplifies the overall circuit configuration. The purpose of the present invention is to provide a modulation/demodulation circuit.

[Means for solving technical problems]

The present invention is a modulation/demodulation circuit using signals whose phases are shifted by 90 degrees from each other, and includes a carrier wave generation means for supplying a carrier wave, and a first . The first signal for superimposing the second signal. a second mixing means;
Above 1. The first . Second
or convert it into a signal of 1. above. The second mixing means is connected downstream of the first mixing means. and a surface acoustic wave filter that provides a phase difference of 90'' between the output signals of the second mixing means.

A surface acoustic wave filter for providing a 90° phase difference is
The two output electrodes or input electrodes may have different distances in the surface wave propagation direction from the manual electrode or the output electrode so as to produce a phase difference of 90'.

More preferably, three or more input/output electrodes are distributed in the surface wave propagation direction, and two output electrodes or manual electrodes are connected to the input electrode in order to generate a 90° phase difference. Alternatively, it is placed on the opposite side of the output electrode in the surface wave propagation direction.

Furthermore, the two output electrodes or the input electrodes may be arranged in parallel in a direction perpendicular to the surface wave propagation direction.

[Operation] Since the means for providing a 90° phase difference is composed of a surface acoustic wave filter with stable characteristics, adjustment of the level difference and phase difference between the two signals to which the phase difference is given is omitted. It becomes possible to do so.

[Explanation of Examples]

FIG. 1 shows a circuit diagram of an embodiment of the present invention.

This embodiment is applied to a direct conversion type demodulation circuit.

Referring to FIG. 1, a high frequency amplifier 22 is connected to an antenna 21 so as to receive a high frequency signal received by the antenna. A surface acoustic wave filter 23 is connected after the high frequency amplifier 22.

The surface acoustic wave filter 23 converts the input high frequency signal into
The first . It is provided for converting into a second high frequency signal.

The structure of this surface acoustic wave filter 23 will be explained later with reference to FIG.

The first and second high frequency signals output from the surface acoustic wave filter 23 are provided to γjX combiners 24 and 25, respectively. A carrier wave oscillator 26 is connected to the mixer 24,25.

In the mixer 24.25, the first. The second high frequency signals are frequency converted and are respectively low pass filtered 27.2.
given to 8.

The circuit configuration after the low-pass filters 27 and 28, ie, the circuit of the hair band portion, is the same as the conventional example shown in FIG. That is, the amplifier 29°30, the differential circuit 31
, 32, mixer 33, 34 are connected, mixer 3
The outputs of 3 and 4 are differentially amplified by a differential amplifier 35 to obtain a demodulated output.

The feature of this embodiment lies in the circuit portion that converts the received high frequency signal into a Haasband signal. That is, the received high frequency signal is filtered by the surface acoustic wave filter 23 into the first . are converted into a second high frequency signal, and each first... The second high frequency signal is the first high frequency signal. It is characterized in that it is frequency converted in the second mixer 24, 25 and dropped into the Haasband.

FIG. 3 is a plan view schematically showing a structural example of the surface acoustic wave filter 23. In the surface acoustic wave filter 23,
On the surface wave substrate 36, three interdigital electrodes each consisting of interdigitated comb electrodes are arranged at predetermined intervals in the surface wave propagation direction. That is, a central manual electrode 38 and output electrodes 37, 39 arranged on both sides of the central input 11i3B are formed. In the surface wave propagation direction, the distance between the output electrode 37 and the manual electrode 38 is 2. and the distance H1 between the output electrode 39 and the manual electrode 38
2 are different from each other so as to give a phase difference of 90° to their output signals. In other words, the distance ji in Figure 3! 2.
and distance Mi2 are configured to differ by 174 wavelengths.

From the structure shown in FIG. 3, since the phase difference of 90'' is due to the delay time difference, in the surface acoustic wave filter 23, if the structures of the output electrodes 37 and 39 are made the same,
．． It can be seen that there is almost no difference in level between the output signals of No. 39, and there is also almost no difference in filter characteristics.

Note that the difference between the distances Itl and lx does not necessarily have to be 1/4 wavelength, but can be any value such as 3/4 wavelength or 5/4 wavelength, as long as a phase difference of ±90° can be obtained.

In addition, the load connected to the output electrode 37 and the output electrode 39
If there is a difference in the loads connected to the
, L may be corrected.

Similarly, even if there is a difference in the output signal level of both output electrodes 37 and 39 due to differences in load conditions, etc., each output electrode 37
．． Correction may be made by changing the electrode crossing width or logarithm in 39. However, the number of electrode fingers in an interdigital electrode is a very important factor in determining the band characteristics. Therefore, it is preferable that the logarithms of both output electrodes 37 and 39 be made the same as possible.

In short, in practical conditions, as long as the output signal levels of the output electrodes 3739 are approximately the same and the phase difference between the two output signals is 90°, the configuration of each electrode and the distance 1. ．． 1.
The second prize can be changed as appropriate.

Although Fig. 3 schematically shows only the structure that provides a phase difference of 90@, it goes without saying that in a practical surface acoustic wave filter, sound absorbing materials, packages, etc. (not shown) may be incorporated as necessary. Not even.

Returning to FIG. 1, in the demodulation circuit of this embodiment, the antenna 21
The high-frequency signal received by the high-frequency amplifier 22 is amplified by the high-frequency amplifier 22 and provided to the surface acoustic wave filter 23 . In the surface acoustic wave filter 23, the two output electrodes 37.3
9 (Fig. 3), the first one with a phase difference of 90° between them.
A second high frequency signal is output.

In this case, the first. The 90° phase difference between the second high frequency signals is provided by the surface acoustic wave filter 23 having the structure described above. That is, since it is given based on the difference in distance l1,1□ from the input electrode 38 of the output electrode 37.39, there is almost no output level difference or phase difference error between the two high frequency signals, and the 90' First and second high frequency signals having a phase difference and having the same signal level are provided with high precision.

Therefore, it is possible to omit complicated adjustment operations such as level adjustment and phase difference error '411i correction, which were necessary when using a conventional 90'' phase shifter.

In addition, it is also possible to omit a large number of circuit components such as the banpha amplifier 8.10 and the bandpass filter shown in FIG.

Next, other structural examples of the surface acoustic wave filter 23 are shown in FIGS.
This will be explained with reference to FIG.

In the surface acoustic wave filter 41 shown in FIG.
On one side, five interdigital electrodes 43~
47 are arranged at predetermined intervals. That is, an input electrode 45 is arranged at the center, output electrodes 44, 46 are arranged on both sides of the input electrode 45, and input electrodes 43, 47 are arranged outside the input electrode 45.

In the surface acoustic wave filter 41 of FIG. 4, the output electrode 44.
Since surface waves based on human input signals are propagated from both sides of the surface wave propagation direction of 46, loss can be significantly reduced. That is, compared to the case of the third surface acoustic wave filter 23,
It is possible to achieve even lower Ti loss.

In the surface acoustic wave filter 41, the main surface wave propagation path is between the input electrode 43 and the output electrode 44 and between the input electrode 45.
- between the output electrodes 44, between the input electrodes 47 and the output electrodes 46, and between the input electrodes 45 and the output electrodes 46, so the illustrated distance '11+'+2 and the distance H1lt1. lzt may be shifted by substantially 1/4 wavelength.

Most importantly, distance #l l 1l=l lt and distance 2□
, 12□, but it is not necessarily limited to these relationships. For example, 1Il=l+t+1 wavelength may be used, that is, '! Il+L2 and j! 21. 1
! As long as it is possible to shift at by 1/4 wavelength, the distance Ll~! 2! can be changed as appropriate.

Also, the surface wave propagation path length, that is, jl! By appropriately varying Lx, it is possible to reduce the reinforcement of multiple reflections between electrodes, and it is also possible to alleviate multiple reflections to some extent.

FIG. 5 shows a third structural example of the surface acoustic wave filter.

In the surface acoustic wave filter 51, on one side of the input electrode 53, on the surface acoustic wave substrate 52, there are two electrodes separated by a distance β.
An output electrode 54 is formed. And input electrode 5
3 and the other output electrode 55 is formed at a distance β. The distance, 1dlN1.12, is set in the same way as in the case of the surface acoustic wave filter 23 in FIG.

In the surface acoustic wave filter 51, output electrodes 5455 are arranged side by side in a direction perpendicular to the surface wave propagation direction. Therefore, it is possible to reduce the size of the surface acoustic wave filter in the surface wave propagation direction by one size.

FIG. 6 shows a fourth structural example of a surface acoustic wave filter.
In the surface acoustic wave filter 61, a manual electrode 63 is formed at the center of a surface wave substrate 62.

Output electrodes 64 and 65 are formed on one side of the input electrode 63 in the surface wave propagation direction, and output electrodes 66 and 67 are formed on the other side. That is, this surface wave filter 61, the fifth
This corresponds to a structure in which the output electrodes 54 and 55 of the surface acoustic wave filter 51 shown in the figure are also arranged on the opposite side of the input surface wave propagation direction.

The surface acoustic wave filter 51 shown in FIG. 5 has the disadvantage that, of the surface waves excited by the manual electrode 53, the surface waves propagating to the side where the output electrodes 54 and 55 are not provided are wasted, resulting in a large insertion loss. There is. On the other hand, in the surface acoustic wave filter 61 shown in FIG. 6, output electrodes are arranged on both sides of the manual electrode 63, so that the insertion loss can be reduced. In addition, the propagation distance is 41! I+"" 471g may be set in the same manner as in the case of FIG.

In surface acoustic wave filters 23, 41, 51, and 61, each input and output electrode is shown as a regular interdigital electrode for convenience, but weighting is applied to improve selectivity characteristics. Alternatively, each electrode finger may be a splint electrode consisting of two or more electrode fingers in order to reduce reflection of surface acoustic waves in the chaotic finger.

Similarly, in order to suppress direct waves generated between input and output electrodes, a shield electrode may be appropriately provided in the surface wave propagation direction.
That is, a characteristic improving structure used in general surface acoustic wave filters can be used as appropriate.

Furthermore, in order to improve insertion loss, a reflector may be used in combination with the transversal type surface acoustic wave filter as described above to form a surface acoustic wave resonator filter.

An example of a surface acoustic wave resonator filter is one in which grating reflectors made of metal strips or groups are arranged outside the input/output electrodes in the surface wave propagation direction of each of the above-mentioned structural examples.

In addition, as shown in Figure 7, a surface wave filter that requires elastic coupling in a direction perpendicular to the surface wave propagation direction may be used. In Figure 7, only the positions of each electrode and reflector are shown schematically. In the surface acoustic wave filter 71 shown in FIG. The output Tl h 75 is formed in the direction perpendicular to the surface wave propagation direction 67 fi-=
79 indicates a reflector.

In this structure, a two-boat type resonator serving as an output electrode 75 arranged in a direction perpendicular to the surface wave propagation direction is arranged close to a human-powered electrode in a direction perpendicular to the surface wave propagation direction, and is arranged in the lateral direction. It is made into a dual mode by utilizing the elastic coupling of. That is, a 90° phase difference is achieved by utilizing the phase difference between the symmetric mode and the antisymmetric mode.

By using a resonator filter as described above, it is possible to reduce the insertion loss. The width becomes narrower. Therefore, 90° over a wide band
When a phase difference of 2 is required, it is preferable to use a transversal type surface acoustic wave filter as described above.

Although the embodiment shown in FIG. 1 is applied to a demodulation circuit of a receiver, the present invention can be similarly applied to a modulation circuit on the transmitter side. An embodiment applied to a modulation circuit is shown in a circuit diagram in FIG.

The circuit shown in FIG. 8 is applied to a four-phase PSK modulation circuit, in which a human data string consisting of a digital signal is input to a plane-difference conversion circuit 81, and the output of the parallel-to-parallel conversion circuit 81 is ．． A second mixer 82, 83 is provided. 1st.
The second mixer 82 , 83 is also given a carrier wave signal from the carrier wave oscillator 84 , and the output signal of the surface difference conversion circuit is balanced-modulated in each mixer 82 , 83 and is given to the surface acoustic wave filter 85 . .

As the surface acoustic wave filter 85, for example, the surface acoustic wave filter 23 shown in FIG. 3 with the input electrode and output electrode reversed can be used. That is, electrode 3 in FIG.
By using 7.39 as the input end and the electrode 38 as the output end, a phase difference of 90° is given to the input signal on the surface acoustic wave filter 23.

A conventional modulation circuit corresponding to the embodiment shown in FIG.
As shown in the figure. Here, in order to maintain a 90° phase difference,
Similar to the conventional example shown in FIG.
However, in the case of an LC filter or the like, circuit adjustments and phase difference errors had to be adjusted. In addition, in FIG. 9, 91 represents a synthesizer, and 92 represents a bandpass filter.

On the other hand, in the embodiment shown in FIG.
Since the phase difference is provided stably and with high precision, 1. It is possible to omit level adjustment and phase error adjustment.

[Effects of the Invention] As described above, according to the present invention, a surface acoustic wave filter is used to provide an α phase difference of 90'' in a modulation/demodulation circuit that uses signals whose phases are shifted by 90''. Therefore, it is possible to stably obtain a phase difference of 90". In other words, since the phase difference of 90" is determined by the distance between the electrodes on the surface acoustic wave filter, it is possible to stably obtain a phase difference of 90". It is possible to obtain a phase difference of 90° much more stably with C1 than with the case using J, and therefore it is possible to omit phase difference errors and signal level adjustments.

Moreover, since it uses a surface acoustic wave filter,
Since it not only provides a phase difference of 906 but also has characteristics as a bandpass filter, it is also possible to reduce the number of parts.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a demodulation circuit according to an embodiment of the present invention, FIG. 2 is a circuit diagram showing an example of a conventional demodulation circuit, and FIG. 3 is a schematic plan view showing an example of the structure of a surface acoustic wave filter. , FIGS. 4 to 7 are schematic plan views showing other structural examples of the surface acoustic wave filter used in the present invention, and FIG. 8 is a circuit diagram of another embodiment of the present invention, and FIG. FIG. 9 is a circuit diagram showing an example of a conventional modulation circuit. In the figure, 23 is a surface acoustic wave filter, 24° and 25 are first . The second mixer, 26, represents a carrier wave oscillator. Part 2

Claims (4)

[Claims] (1) A modulation/demodulation circuit using signals whose phases are shifted by 90 degrees from each other, comprising a carrier wave generating means for supplying a carrier wave, and first and second signals for superimposing the first and second signals on the carrier wave. a mixing means, and a first and second mixing means connected upstream of the first and second mixing means and having input signals shifted in phase by 90 degrees from each other.
or a surface acoustic wave filter connected after the first and second mixing means and providing a phase difference of 90° between the output signals of the first and second mixing means; A modulation/demodulation circuit comprising: (2) The surface acoustic wave filter has two input electrodes or output electrodes, and the distances of the two input electrodes or output electrodes from the output electrode or the input electrode in the surface wave propagation direction are made different from each other. The modulation/demodulation circuit according to claim 1, wherein the modulation/demodulation circuit is configured to obtain a phase difference of 90 degrees. (3) The surface acoustic wave filter has at least three input and output electrodes arranged at a predetermined distance in the surface wave propagation direction, and has two
3. The modulation/demodulation circuit according to claim 2, wherein the output electrodes or the input electrodes are arranged on opposite sides of the input electrode or the output electrode in the surface wave propagation direction. (4) Two output electrodes or input electrodes of the surface acoustic wave filter for giving a phase difference of 90 degrees to each other are arranged in parallel in a direction orthogonal to the surface wave propagation direction. , The modulation/demodulation circuit according to claim 2.