JPH0311808A - Modulation and demodulation circuit - Google Patents

Abstract

PURPOSE:To omit the adjustment of a level difference and a phase difference of two signals, to attain no adjustment of a 90 deg. phase shifter and to simplify the circuit constitution by using a surface acoustic wave filter in a MODEM circuit using signals deviated by 90 deg.. CONSTITUTION:A surface acoustic wave filter 26 connects to a carrier oscillator 25 to supply a carrier signal for the conversion of a base band at multipliers 23, 24. The surface acoustic wave filter 26 converts a supplied carrier signal into 1st and 2nd carrier signals whose phases are shifted by 90 deg. and they are outputted. Since the phase difference of 90 deg. depends on the electrode distance of the surface acoustic wave filter, the phase difference of 90 deg. is far stably obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a modulation/demodulation circuit that performs angular modulation or demodulation using two signals having a phase difference of 90".
This invention relates to a surface acoustic wave filter using a surface acoustic wave filter as 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) is it relatively good? (b) requires an expensive element such as a crystal filter as an intermediate frequency band filter, and (c) requires an intermediate frequency stage of L.
There was a drawback that it was difficult to convert to SI. As a result, it was difficult to realize miniaturization and cost reduction.

On the other hand, a direct conversion type variable viff1 circuit is being considered as a system that is suitable for integrating up to the baseband part into an LSI, and can achieve downsizing and cost reduction. 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 filtered high frequency signals that are amplified by and filtered by the high frequency bandpass filter 3 are applied to mixers 'a4 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 buffer amplifier 8 is also provided to 90° phase shifter 9. 90@phase shifter 9
The second carrier signal whose phase is shifted by 90° is applied to the other mixer 4 via the buffer amplifier IO.

Then, the received signals immediately dropped into Haasband by mixers 4 and 5 are passed through low-pass filters 11 and 11, respectively.
given to. After the low-pass filters 11.12, amplifiers 13.14. Differentiator circuit 15.16 and mixer 1
7.18 is connected, mixer 17,! 8 is amplified by the differential amplifier 19 to obtain a demodulated output.The above configuration does not require an intermediate frequency stage (amplifier, intermediate frequency filter, etc.) used in the foothetero gain method. , the circuit section after the part indicated by the broken line A, that is, the configuration after the baseband section can be configured as a one-chip 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 90° phase shifter 9 connected to the carrier wave oscillation circuit 6 poses a problem. That is, the 90" 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 oscillator 6 generally includes spurious signals, a tank circuit (bandpass filter) consisting of an LC is provided at the output. Because of mutual interference, it was necessary to insert a buffer amplifier 8 in between. 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]

a carrier wave generating means for supplying a carrier wave; and a first . a surface acoustic wave filter that converts the signal into a second carrier signal; and a surface acoustic wave filter that is connected to the surface acoustic wave filter so as to receive the first or second carrier signal from the surface acoustic wave filter; A first device that modulates and demodulates a human input signal of No. 2 using a first or second carrier signal.
, and second multiplication means.

The surface acoustic wave filter for giving a phase difference of 90@ is:
The two output electrodes may be configured to have different distances in the surface wave propagation direction from the manual 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 for generating a 90° phase difference are arranged relative to the manual electrode, They are placed on opposite sides in the surface wave propagation direction.

Furthermore, the two output electrodes may have a structure in which they are arranged in parallel in a direction orthogonal to the surface wave propagation direction.

[Effect]

Since the means for giving a 90° phase difference is composed of a surface acoustic wave filter with stable characteristics, it is possible to adjust the level difference between the two signals that give the phase difference and adjust the phase difference. It can be omitted.

[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. The output side of the high frequency amplifier 22 is branched into first . It is connected to a second multiplier 23.24.

On the other hand, in order to supply a carrier signal for conversion to baseband in multipliers 23 and 24, a carrier wave oscillator 25,
The zero surface acoustic wave filter 26 to which the surface acoustic wave filter 26 is connected converts the supplied carrier wave signal into a first... It is configured to convert it into a second carrier wave signal and output it.

This first carrier wave signal is applied to the first multiplier 23, and the second carrier wave signal is applied to the second multiplier 24.゜2
4 is connected to the output terminal of the surface acoustic wave filter 26. The structure of the surface acoustic wave filter 26 will be explained later with reference to FIG.

1st. In the second multiplier 23.24, the high frequency amplifier 22
The first or second human power signal provided by the first or second carrier signal G is modulated by the first or second carrier signal G, respectively, and directly converted to baseband.

1st. A low-pass filter 27.28 is connected to the downstream stage G2 of the second multiplier 23.24, respectively. The circuit configuration after the low-pass filters 27 and 28, ie, the baseband circuit, is the same as the conventional example shown in FIG.

That is, amplifiers 29 and 30, differentiating circuits 31 and 32, and mixers 33 and 34 are connected, and the output of the mixers 33 and 34 is differentially amplified by a differential amplifier 35 to obtain a demodulated output. has been done.

The feature of this embodiment lies in the circuit portion that converts the received high frequency signal to baseband. That is, in the 1st and 2nd multipliers 23 and 24, the received high frequency signal is input to the 1st and 2nd multipliers 23 and 24 to which the surface acoustic wave filter 26 gives a phase difference of 90°. It is characterized in that it is dropped to the baseband by being multiplied by the second carrier signal.

FIG. 3 is a plan view schematically showing a structural example of the surface acoustic wave filter 26. In the surface acoustic wave filter 26,
On the surface wave substrate 36J, three interdigital electrodes made of interdigitated comb electrodes are arranged at predetermined intervals in the surface wave propagation direction. That is, a central input electrode 38 and outputs 1ui37.3B arranged on both sides of the central input electrode 38 are formed. Then, then,
In the surface wave propagation direction: 1. Output electrode 37 - manual electrode 3
The distance between 8! , and the distance 2□ between the output electrode 39 and the manual electrode 38 are made different so as to give a phase difference of 90° to the output signals. That is, distance 1 in FIG.
And distance! The two wavelengths are different from each other by 1/4 wavelength.

From the structure of FIG. 3, since the 90° phase difference is formed by the delay time difference, in the surface acoustic wave filter 26, if the output electrodes 37.39 have the same structure, the output electrodes 37.39. 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.

In addition, the distance I! ,,j! The difference in width does not necessarily have to be 1/4 wavelength, but can be ±90° such as 3/4 wavelength or 5/4 wavelength.
Any value is acceptable as long as it provides a phase difference of .

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
i,,f, may be corrected.

Similarly, even if there is a difference in the output signal level of both output electrodes 3739 due to a difference in load conditions, etc., each output electrode 37.
Correction may be made by changing the electrode crossing width and the logarithm in the interdigital electrode. However, the logarithm of the electrode fingers in the interdigital electrode is a very important element 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 Okayama force signals is 90°, the configuration of each electrode and the distance mz,,z,
can be changed as appropriate.

Although FIG. 3 schematically shows only the structure that provides a 90° phase difference, it is understood 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 first . It is applied to a second multiplier 23,24. On the other hand, from the surface acoustic wave filter 26, from its two output electrodes 37°39 (FIG. 3), a first. A second carrier signal is output.

In this case, 1. The 90' phase difference between the second carrier signals is provided by the surface acoustic wave filter 26 having the structure described above. In other words, since it is given based on the difference in distance #1.2□ from the output electrode 38 of the output type 8i37.39, there is almost no output level difference or phase difference error between the recarrier signals, and the 90 First and second high frequency signals having a phase difference of .degree. and having the same signal level are provided with high precision.

Therefore, it is possible to omit the complicated adjustment work such as level adjustment and phase difference error correction, which were necessary when using the 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 26 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 shown in FIG. 4, the output electrodes 44,
Since surface waves based on 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 surface acoustic wave filter 26 in FIG.
It is possible to achieve even lower 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 ll l + l l 2 and the distance H1z+, ext
What is necessary is to shift them by substantially 1/4 wavelength.

In general, the distance j! ++=Lt and distance 1. -E■, but it is not necessarily limited to these relationships 0 For example, 2□-j! It may be 1□+1 wavelength,
That is, l I l + l I K and 2□, 10
Distance as long as it is possible to shift the and by 1/4 wavelength! ,~
10 can be changed as appropriate.

Further, by appropriately varying the surface wave propagation path lengths, that is, 2□ to io, 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 a surface acoustic wave filter.
In the surface acoustic wave filter 51, l output electrodes 54 are formed on a surface wave substrate 52 on one side of an input electrode 53, separated by a distance M tz +. The other output electrode 55 is formed separated from the input electrode 53 by a distance Mlt. The distances i1 and l□ are 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 54 and 55 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.

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

Output electrodes 64 and 65 are formed on one side in the surface wave propagation direction of the input ti 63, and output electrodes 66 and 67 are formed on the other side. That is, this surface wave filter 61
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 surface acoustic wave propagation direction from the input electrodes.

The surface acoustic wave filter 51 shown in FIG. 5 has the disadvantage that of the surface waves excited by the input 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, the output electrodes are arranged on both sides of the input electrode 63, so that the insertion loss can be reduced. Note that the propagation distance 1. ~! 18 may be set in the same manner as in the case of FIG.

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

Similarly, in order to suppress direct waves generated between input and output electrodes, a shield bridge may be appropriately provided in the surface wave propagation direction.

That is, the characteristic improving structure used in the -C surface acoustic wave filter can be used as appropriate.

Furthermore, in order to improve insertion loss, a reflector may be used in combination with the transpernal 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 a grating reflector made of a metal string or group is 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. An output electrode 75 is formed in a direction perpendicular to the surface wave propagation direction. 76 to 79 indicate reflectors.

In this structure, a two-boat resonator serving as an output electrode 8i75 is arranged in a direction perpendicular to the surface wave propagation direction, and is arranged close to the input electrode in a direction perpendicular to the surface wave propagation 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 insertion loss, but -S has a narrow band when used as a resonator filter, and a band that can realize a phase difference of 90''. The width is narrower.Therefore, over a wide range of 90'
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 an input data string consisting of a digital signal is input to a serial-to-parallel converter circuit 81.
The output of is the first. A second multiplier 82,83 is provided.

On the other hand, the carrier wave signals generated by the carrier wave oscillator 84 are filtered by a surface acoustic wave filter 85 into the first . converted into a second carrier signal. and,
This first. The second carrier signals are connected to the first . Second
Multiplier 82. Awarded in '83. Therefore, the first. In the second multiplier 82, 83, the first . The second input signal is the first input signal. Modulated by a second carrier signal. In addition, in FIG. 8, 86 indicates an adder.

A conventional modulation circuit corresponding to the embodiment shown in FIG.
As shown in the figure. Here, in order to give a phase difference of 90 degrees to the carrier wave signal, a carrier wave oscillator 87 is used as in the conventional example in FIG.
In addition, bandpass filter 88, buffer amplifier 89.90
and a 90″ phase shifter 91.
When the ° phase shifter 91 is composed of an LC filter or the like, it is necessary to perform circuit adjustment and phase difference error adjustment. Note that in the ninth episode, 86 represents an adder and 92 represents a bandpass filter.

On the other hand, in the embodiment shown in FIG.
Since a phase difference of 0° is provided stably and with high precision, level adjustment and phase difference error adjustment can be omitted. Moreover, since the surface acoustic wave filter 85 itself also has a function as a bandpass filter, the bandpass filter 88 in FIG.
92 can also be omitted.

〔Effect of the invention〕

As described above, according to the present invention, in a modulation/demodulation circuit that uses signals whose phases are shifted by 90 degrees, a surface acoustic wave filter is used to provide a 90 degree phase difference. A stable phase difference can be obtained. In other words, the 90" phase difference is determined by the distance between the electrodes on the surface acoustic wave filter, so compared to the case where other phase shifters such as LC filters are used. , it is possible to obtain a 90° phase difference much more stably, 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 90@ 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, 23.24 is the first. The second multiplier, 25 is a carrier wave oscillator, and 26 is a surface acoustic wave filter. Figure 3

Claims (4)

[Claims] (1) A modulation/demodulation circuit using signals whose phases are shifted by 90 degrees from each other, comprising a carrier wave generation means for supplying a carrier wave, and a modulation/demodulation circuit that is connected to the carrier wave generation means and transmits carrier filtered signals so that their phases are shifted by 90 degrees from each other. A surface acoustic wave filter that converts into shifted first and second carrier signals; and a surface acoustic wave filter connected to the surface acoustic wave filter so as to receive the first or second carrier signal from the surface acoustic wave filter, respectively. 1. A modulation/demodulation circuit comprising: first and second multiplication means for modulating and demodulating the first or second input signal using the first or second carrier signal. (2) The surface acoustic wave filter has two output electrodes, and the distance of the two output electrodes from the input electrode in the surface wave propagation direction is made different, so that the 90° phase difference can be obtained. 2. The modulation/demodulation circuit according to claim 1, wherein the modulation/demodulation circuit is configured to (3) The surface acoustic wave filter has at least three input/output electrodes arranged at a predetermined distance in the surface wave propagation direction, and two electrodes for generating a phase difference of 90° between them.
3. The modulation/demodulation circuit according to claim 2, wherein the output electrodes are arranged on opposite sides of the input electrode in the surface wave propagation direction. (4) Two output electrodes of the surface acoustic wave filter for giving a phase difference of 90° to each other are arranged in parallel in a direction perpendicular to the surface wave propagation direction.
The modulation/demodulation circuit according to claim 2.