JPH0685697A - Radio transmitter - Google Patents

Abstract

PURPOSE:To obtain a radio transmitter capable of employing a carrier wave in which a higher harmonic on the feedback loop of an oscillator can be suppressed without providing an expensive filter. CONSTITUTION:Only one IDTc out of plural IDTc and IDTd provided on a SAW element Y3 is used as the feedback part 10 of an oscillator 5 for carrier generation, and a signal excited from another IDTd is used as the carrier. Thereby, it is possible to obtain a small and inexpensive radio transmitter capable of using the carrier in which a higher harmonic level can be sufficiently suppressed by suppressing the higher harmonic generated on the feedback loop of the oscillator 5 for carrier generation by the SAW element Y3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio transmitter using a SAW element as a carrier wave generation oscillator.

[0002]

2. Description of the Related Art Currently, in the case of a wireless transmitter without a license, the allowable value of the radiated electric field strength is specified for each frequency by the Radio Law Enforcement Regulation in Japan, and the allowable value is small, but the wireless station is very small and inexpensive. Therefore, it is widely used as a simple communication and remote control means.

Such a wireless transmitter has a communication capacity of 300 [MH
It is effective to extend the communication distance with a small antenna if a high frequency near z] is used, but 322 [MHz]
10 [GH] over the following frequencies and 322 [MHz]
The allowable values of the electric field strengths at frequencies below z] are 500 [μV / 3 [m] away from the wireless transmitter.
m] and 35 [μV / m] or less are stipulated by the Radio Law Enforcement Regulations. Therefore, 322 [MH
z], the difference in the allowable value of the electric field strength is 23 [d
B] Since there is a wireless transmitter, for example, 300 [MHz]
When using the carrier wave of the maximum level of the specified value of, the oscillator for generating the carrier wave is 600 [M
It is necessary to suppress [Hz] by 23 [dB] or more.

For this reason, when the crystal oscillator is used as a carrier wave generation oscillator, the highest resonance frequency that can be directly oscillated by the crystal oscillator is currently about 50 [MHz], so that a carrier wave of, for example, 300 [MHz] is obtained. Therefore, it is necessary to multiply the oscillation output of 50 [MHz] by 6.
Moreover, since the oscillator and the multiplier are generally used in a saturated state, the harmonic level thereof is large, and the original vibration is 50 [MH].
Many harmonics of z] are also included. Therefore, in order to satisfy the conditions of the Radio Law, it is necessary to suppress not only the harmonic components of 300 [MHz] but also the harmonic components of 50 [MHz] higher than the harmonic components. Therefore, there is a problem that the manufacturing cost of the wireless transmitter increases.

In a radio transmitter which does not require frequency accuracy as high as that of a crystal oscillator, the cost for filtering and multiplication caused by suppressing the harmonic component of 50 [MHz] is eliminated, so that multiplication is not performed. However, by using a SAW oscillator that can directly obtain an oscillation output of 300 [MHz] or more as a carrier wave generation oscillator, spurious components near the carrier wave can be removed and the price of the wireless transmitter can be reduced. it can.

That is, in order to achieve this object, a conventional radio transmitter has a 1-port SAW element Y ₁ as shown in FIG.
_A feedback unit 1 in which capacitors C _A and C _B are combined is connected between an output end and an input end of the amplification unit 2, and a signal of a frequency based on a component parameter of the feedback unit 1 is supplied to the amplification unit 2. It was taken out from the output end and supplied to the harmonic suppression filter for use as a carrier wave. Further, as an oscillation circuit system, there is a feedback type oscillation circuit as shown in FIG. 3 in addition to the Colpitts type oscillation circuit described above. As shown in the figure, the feedback section 3 is composed of a 2-port SAW element Y ₂ , and the S
An amplifier 4 is provided at both ends of IDTa and b of the AW element Y _2.
The input terminal and the output terminal are connected to each other, and the signal of the resonance frequency of the SAW element Y ₂ is taken out from the output terminal of the amplification section 4 and supplied to the harmonic suppression filter for use as a carrier wave. According to the oscillating circuit using the SAW element capable of directly oscillating the desired frequency, the harmonics generated as spurious waves are twice as many as those of the carrier, so that the cost is relatively low like an LC filter.

However, such a radio transmitter system requires a filter which is simple and low in cost for suppressing high-level harmonics with a sufficient attenuation rate based on the above-mentioned radio law, and therefore needs to be miniaturized. However, the cost is still insufficient for the purpose of simple communication and remote control means.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the problems of the conventional wireless transmitter as described above, and uses an oscillator capable of generating a carrier wave in which harmonics are suppressed to a desired level. This eliminates the need for filters,
Therefore, it is an object of the present invention to provide a wireless transmitter which can be further reduced in size and cost.

[0009]

SUMMARY OF THE INVENTION To achieve the above object, a wireless transmitter according to the present invention includes one of a plurality of IDTs included in a SAW element.
Only one is used for the feedback part of the oscillator for carrier generation, and the other I
It is configured to use the signal excited from the DT as a carrier.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on the embodiments shown in the drawings. FIG. 1 is a circuit diagram showing an embodiment of a wireless transmitter of the present invention. In the present embodiment, the modulation means is omitted for ease of explanation. In the figure, reference numeral 5 denotes a carrier wave generation oscillator including a Colpitts type oscillation circuit 6 and a 2-port SAW element Y _3, which is one of the IDTc of the SAW element Y ₃ , a transistor Tr ₁ , a coil L and a capacitor C _1. To C ₄ and bias resistors R _{1 to} R ₄ are connected to each other to form the Colpitts oscillator circuit 6, and the SAW
Both ends of the other IDTd of the element Y ₃ are used as output ends of the carrier wave generation oscillator 5. An output circuit 8 including an amplifier 7 in which a transistor Tr ₂ , capacitors C ₅ and C ₆ and bias resistors R _{5 to} R ₇ are connected to each other and an antenna (not shown)
Is connected to the output end of the carrier wave generation oscillator 5, and the radio transmitter is configured to supply the signal generated at both ends of the IDTd to the antenna via the amplifier 7.

The wireless transmitter configured as described above operates as follows. That is, the wireless transmitter can represent an equivalent circuit of the Colpitts type oscillation circuit 6 as shown in FIG. 4, the transistor Tr ₁ functions as the amplification section 9 of the oscillation circuit 6, and the capacitors C _{1 to} C ₄ and IDTc. And coil L
Functions as the feedback unit 10 of the oscillator circuit 6, and thus generates a fundamental wave S having a desired frequency according to the oscillation conditions of these circuit parameters and a harmonic wave N caused by stray capacitance. On the other hand, the SAW element Y ₃ has an ID due to the fundamental wave S and the harmonic wave N.
Tc is excited to generate a surface acoustic wave, but SAW element Y
_Since only the surface acoustic wave caused by the signal component having the same frequency as the resonance frequency of ₃ is transmitted to the IDTd, only the fundamental wave S can be generated at both ends of the IDTd. Moreover, since this wireless transmitter uses the signal extracted from the feedback loop of the Colpitts oscillator circuit 6 through the SAW element Y ₃ as a carrier wave, it is possible to provide a harmonic elimination filter unlike the conventional one. The harmonic wave N can be suppressed with a high attenuation rate based on the signal transfer characteristic of the SAW element Y ₃ from IDTc to d, and the radio transmitter can be downsized.

Further, in this radio transmitter, even if the level of the harmonic wave N on the feedback loop of the Colpitts oscillator circuit 6 is about the level of the fundamental wave S, only the fundamental wave S is output from the output end of the carrier wave generation oscillator. The harmonics N are generated by the SAW element Y ₃
Therefore, the feedback gain of the Colpitts oscillator circuit 6 can be increased to stabilize the oscillation operation.

Further, this radio transmitter sets each of the above circuit parameters in the following table.

[0014]

[Table 1]

According to the result of the experiment for transmitting the carrier of 300 [MHz] from the antenna,
The ratio of the fundamental wave to the harmonic wave on the feedback loop was 3 [dB], but 20 [dB] could be obtained at the output end of the amplifier. That is, the above-mentioned wireless transmitter transmits harmonics at 3 [d
B] By providing a suppressible low-cost antenna or attenuator, it is possible to miniaturize the unlicensed wireless transmitter stipulated by the Radio Law.

Further, although the two-port SAW element is used in the above-mentioned embodiment, the present invention is not limited to this, and a SAW element having a plurality of IDTs is used as an oscillator for carrier wave generation, and the feedback section of the oscillator is used. Only one of the plurality of IDTs may be used and a signal excited by another IDT may be used as a carrier. For example, as shown in FIG. 5, a SAW element Y ₄ having a plurality of IDTe ₀ , e ₁ , e ₂ , ... And e _-1 , e _-2 , ... Is provided in place of the SAW element Y _3.
Both ends of DTe ₀ are connected to the feedback section 10 of the carrier wave generation oscillator 5, and both ends of the other IDTs are connected to the output circuit 8 via the selector 11 so that the other IDTs can be output according to the information to be modulated. If the selector 11 is controlled to supply one or a plurality of carrier waves excited by the output circuit 8, a pulse amplitude modulated wave, a pulse phase modulated wave, or a modulated wave in which these are combined is illustrated. Can be sent from the antenna without. Further, in this embodiment, it is convenient to use the SAW element which has a predetermined relationship between the phase and the amplitude of the signal excited by each IDT.

Although the Colpitts type oscillating circuit is used as the carrier wave generating oscillator in the above-mentioned embodiment, the present invention is not limited to this, and may be a Hartley type or a feedback type oscillating circuit, or a SAW element. It would be convenient to enhance the effect of suppressing harmonics by using an IDT pattern designed so that the coupling capacitance between the IDT terminals becomes small.

Further, the present invention does not need to limit the scope of its use to the above-mentioned unlicensed wireless transmitter,
It will be obvious that it may be used as a wireless transmitter for communication and remote control.

[0019]

As described above, the present invention provides a plurality of I's.
By using a SAW element having a DT for a carrier wave generating oscillator, using only one of the plurality of IDTs in the feedback section of the oscillator, and using a signal excited by another IDT as a carrier wave. Even if a harmonic is generated on the feedback loop of the oscillator, this harmonic is suppressed by the SAW element, so in order to miniaturize the wireless transmitter that can use the carrier whose harmonic level is sufficiently suppressed. It is very effective.

[0020]

[Brief description of drawings]

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

FIG. 2 is a configuration diagram for explaining a Colpitts type oscillation circuit using a conventional 1-port SAW element.

FIG. 3 is a configuration diagram for explaining a feedback type oscillation circuit using a conventional 2-port SAW element.

FIG. 4 is an equivalent circuit diagram for explaining the operation of the embodiment of the present invention.

FIG. 5 is a configuration diagram showing another embodiment of the present invention.

[Explanation of symbols]

5 Carrier wave generation oscillator, 6 Colpitts oscillation circuit, 8
Output circuit, Y ₃ SAW element, c and d IDT.

Claims (3)

[Claims] 1. A wireless transmitter using a SAW element having a plurality of IDTs for a carrier wave generation oscillator, wherein only one of the plurality of IDTs is used for a feedback section of the carrier wave generation oscillator. A radio transmitter characterized in that a signal excited from the IDT is used as a carrier wave. 2. The radio transmitter according to claim 1, wherein a signal excited by at least one of the other IDTs is supplied to the antenna directly or via an output circuit. 3. The SAW element, wherein the positional relationship between the IDTs is set so that the phases and amplitudes of the signals excited by the IDTs have a predetermined relationship with each other, is used for transmitting information. The wireless transmitter according to claim 1, wherein