JPH03196719A - Radio transmitter-receiver - Google Patents

Abstract

PURPOSE:To reduce number of parts and to avoid production of side tone attended therewith by applying a low frequency input signal to a discriminator coil of an FM demodulation detector via a variable capacitor. CONSTITUTION:A transmission low frequency input signal inputted via a microphone 24 is given to a modulation circuit 22 modulating a local oscillating frequency FL1 generated from a local oscillation circuit 13 and a modulated transmission frequency FT radiates from an antenna 10. On the other hand, a heat signal is obtained from a reception frequency FR inputted from the antenna 10 with respect to the frequency FL1 from the circuit 13 to form an intermediate frequency FIF1 in the mixer 12. On the other hand, a low frequency input signal from a microphone 24 is applied via a variable capacitor VC to a discriminator coil L1 provided to a detector 16 being an FM demodulation circuit whose frequency is FIF1. Thus, a side wave component on the frequency FIF1 is cancelled by the detector 16. Furthermore, since the circuit 13 is used in common for the transmission and reception, number of parts is reduced.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention provides a wireless transmitter/receiver that performs full-duplex communication, such as a cordless telephone, by using a crystal oscillator ( The present invention relates to improvements in reducing the number of PLL (phase locked loop) circuits using crystals or PLL circuits using the same, and their associated circuits.

[Prior Art] When a heterodyne is used in the reception system of a wireless transmitter/receiver that performs full-duplex communication, in the most basic and classic circuit configuration, it is necessary to stably obtain the local oscillation frequency for the heterodyne. crystal oscillator or PL using it
The L circuit (hereinafter referred to as a "crystal oscillator etc." when collectively described) and the crystal oscillator etc. for stably obtaining the transmission frequency require separate dedicated devices.

In addition, if it is a single heterodyne, it is sufficient to use two crystal oscillators, one for the receiving system and one for the transmitting system, but if it is a double heterodyne, an additional one on the receiving system side is required. In order to stably obtain the first and second local oscillation frequencies, each of them has its own separate crystal oscillator, etc., so in the end, a crystal oscillator, etc. is used to stably obtain the carrier frequency of the transmission system. In total, three crystal oscillators are required.

However, although it has become much cheaper recently,
Such crystal oscillators and PLL circuits are still expensive.

Therefore, conventionally, at least in the case of a single heterodyne, two are combined into one, and in the case of a double heterodyne, three are combined into two, and somehow those crystal oscillators or P
Various attempts have been made to reduce the number of LL circuits. Of course, reducing the number is desirable not only in terms of cost, but also in terms of circuit simplification and device miniaturization.

Under such circumstances, assuming that double heterodyne (super heterodyne) is used in the receiving system, the proposal shown in Figure 2 is considered to be practical and representative. There is a transmitting/receiving device as shown in .

Simply put, this means that the first local oscillation frequency FLI given to the first mixer 12 of the receiving system is also used as it is as the carrier frequency F of the transmitting system.

That is, a low frequency input signal for transmission which is converted into an electrical signal via the microphone 24 and amplified via a suitable low frequency amplifier (AF amplifier) 23 is converted into an electric signal whose frequency is stabilized by the crystal oscillator X. 1 generated by the local oscillation circuit 13
It is applied to a modulation circuit 22 that modulates the local oscillation frequency FLI, and then from the modulation circuit 22 to a high frequency amplification circuit (T
RF amplifier for X) 2! is radiated from the antenna lO via the

In the end, the first local oscillation circuit 13 has a transmission carrier frequency FT.
It is also used as a generation circuit for the transmission carrier frequency FT.
is equal to the first local oscillation frequency FLI, so
In the basic or classical configuration prior to this conventional example, two crystal oscillators, etc., which were required to be used separately for each, can be used as one.

However, in this case, the modulation component due to the input signal information from the microphone 24 is naturally transmitted to the first mixer 12 on the receiving side.
It will also be added to Therefore, if no countermeasures are taken against this, a problem will occur on the receiving system side.

In other words, the reception frequency FR input from the antenna 10 is
After appropriately passing through a high frequency amplifier (RF amplifier for RX) 11, it is input to a first mixer 12, where it is beatted with the first local oscillation frequency FLI generated by the first local oscillation circuit 13, and is converted into a first intermediate signal. The frequency becomes F + □, and this is further sent to the subsequent second mixer 14, but at this time, if the first local oscillation frequency FLI itself contains a modulation component due to the low frequency input signal on the transmitting side, of course , which also rides on this first intermediate frequency F, □, therefore, the audible acoustic information output from the speaker 18 after being demodulated from the second mixer 1 (from the detector 16) includes:
The audible information input to the microphone 24 side is picked up as "sidetone."

Therefore, in the conventional example shown in this 's2 diagram, the receiving system uses a second crystal oscillator whose oscillation frequency is stabilized by two
A second modulation circuit 31 equivalent to the modulation circuit 22 for transmission carrier modulation described above is also inserted in the line of the second local oscillation frequency signal FL2 from the local oscillation circuit 15 to the second mixer 14. ing.

In this way, in the second mixer 14, the modulated wave component on the transmission system side intervening in the first intermediate frequency FfPI is canceled out, and the second intermediate frequency FIrz without sidetone components can be obtained. can.

However, in order to satisfy this, it is necessary in principle for both the first and second modulation circuits 22 and 31 to have the same degree of modulation. This can be done relatively easily using a circuit system, such as level adjustment using a simple potentiometer circuit.

Of course, the second intermediate frequency or the final fixed frequency F1, 2 obtained above is demodulated by the detector 16 and then sent to an electro-acoustic conversion means as an information reproducing terminal, generally a speaker. 18 as an audible information signal.

On the other hand, a conventional example as shown in FIG. 3 has been proposed as a configuration that can be used even when the heterodyne system employed in the receiving system is a single heterodyne system.

In the figure, the same reference numerals as in FIG. 2 indicate constituent elements that may be the same or similar to those in the previous conventional example, and some of them may not be explained again. Similarly to the example, the local oscillation circuit 13 also serves as a transmission carrier frequency generation circuit, and the low frequency input signal input to the microphone 24 is transmitted to the transmission carrier frequency FTE(
"FLI)" is modulated by a modulation circuit 22, and the result is amplified by an appropriate RF amplifier 21 and then radiated from an antenna IO.

Therefore, like the previous conventional example, the local oscillation frequency FLI output from the local oscillation circuit 13 is modulated by the information signal to be transmitted from the microphone 24 side, and then the mixer on the receiving system side 12, the modulation component is added to the intermediate frequency FIP+, which is the output of the mixer 12, as a sidetone.

Therefore, in the conventional example shown in FIG. The canceller 19 is designed to remove the sidetone components.

In this case as well, the adjustment of the amount of cancellation by level adjustment or the like can be done by the relatively simple compensation circuit 33, as in the prior art example.

[Problems to be Solved by the Invention] Among the two conventional examples described above, the first conventional example shown in the second figure has the disadvantage that it can only be used in a wireless transmitting/receiving device having a receiving system with a double heterodyne configuration. be.

In particular, recently, surface acoustic wave filters (SAW filters) have been used to provide receiving systems that exhibit narrow band characteristics even at high frequencies, so transmitter/receivers that have sufficient receiving characteristics even with single heterodyne are being provided. but,
The configuration of the conventional example shown in the second figure cannot be used for such a device, even in view of the principle described above.

On the other hand, the second conventional example shown in FIG. 3 can be adopted for either single or double heterodyne systems, but it uses an AF amplifier that is connected after the canceller 19 and applies well-known de-emphasis during FM demodulation. The amount of cancellation is easily influenced by the frequency characteristics of the detector 17, and distortions generated in the front-stage detector 16, such as nonlinear distortion and gain distortion due to temperature changes, cannot be canceled.

[Means for Solving the Problems] In order to eliminate both the drawbacks of the conventional example described above, the present invention has a receiving system and a transmitting system, and within the receiving system, a receiving frequency and a local oscillation frequency are connected. The transmission system includes a mixer means for taking the beat of the signal and finally generating a fixed intermediate frequency, and a detector for demodulating the intermediate frequency, and the transmission system modulates the transmission carrier frequency with a low frequency input signal. In a type of wireless transmitting/receiving device that can be defined as a "wireless transmitting/receiving device that includes a modulation circuit," the transmitting carrier frequency modulated by the low-frequency input signal as described above is also used as the local oscillation frequency of the receiving system. , when trying to reduce the number of crystal oscillators, PLL circuits attached to them, etc. by giving this to the mixer means, the input signal component on the transmitting system side that rides on the intermediate frequency of the receiving system,
In other words, we propose the following configuration as a new device for removing sidetone components.

First, a varicap is connected to a discriminator coil that is attached to a detector for FM demodulating intermediate frequencies on the receiving system side.

Then, a low-frequency input signal that modulates the transmission carrier frequency is applied through this varicap, and this modulates the resonant frequency of the resonant circuit including the discriminator coil, thereby changing the mixer output. The sidetone component due to the transmitting side input signal mixed in the intermediate frequency is canceled out.

Furthermore, various types of FM demodulation detector integrated circuits (detector ICs) that are commercially available these days do not have a discriminator or
Since the coil is externally attached, the varicap required for the present invention can be easily attached, and such a detector IC can be conveniently used as is.

Of course, the configuration of the present invention as described above can be applied both to a wireless transmitter/receiver that uses a single heterodyne system in its reception system and to one that uses a double heterodyne system. This is because the sidetone is removed in the detector section that demodulates the intermediate frequency that is finally fixed.

[Function] In the present invention, since the transmitting carrier frequency modulated by the input signal is also given to the mixer means as the local oscillation frequency of the receiving system, the crystal oscillator used for generating the transmitting carrier frequency Alternatively, the PLL circuit and the one for generating the local oscillation frequency on the receiving system side can be shared with each other and do not need to be provided separately, resulting in savings. As far as this point is concerned, it is similar to each of the conventional examples shown in FIGS. 2.3.

However, on the other hand, the removal of the sidetone component as a modulation component on the transmitting side that is present in the intermediate frequency that is ultimately fixed in the receiving system is completely different from the method shown in each of the conventional examples described above. Follow different principles.

That is, in the present invention, a varicap is connected to a discriminator coil that is essential to a detector for FM demodulation, and a low frequency input signal modulating the transmission carrier frequency is applied via the varicap. Therefore, the resonant frequency of the resonant circuit including the discriminator coil is modulated by the input signal component on the transmitting side, thereby canceling out sidetone components that may be mixed in the intermediate frequency on the receiving system side.

Therefore, whether the heterodyne system adopted on the receiving system side is double heterodyne or single heterodyne has no relation to the sidetone cancellation principle of the present invention. The present invention can be applied to both the single heterodyne method and the single heterodyne method.

In addition, sidetone components are removed by modulating the resonant frequency of the resonant circuit, including the discriminator coil, which is directly involved in demodulation, depending on the input signal to be transmitted. It is difficult to be affected by the frequency characteristics of the amplifier, and it is also difficult to be affected by distortion generated by the detector itself.

Furthermore, the present invention is directed toward a simple circuit configuration, and the connection between the varicap and the discriminator coil is also simple.
In reality, this can be achieved by adding several auxiliary capacitors.

[Embodiment] An embodiment of the present invention will be described below with reference to FIG. 1, but the same reference numerals as in FIG. In particular, the constituent elements shown here indicate those that do not require modification or may be the same as those in the conventional example, and in some cases, the explanation for the previous conventional example will be referred to with respect to them, and this section will refer to them. Some explanations may be omitted.

This embodiment shown in Figure 1 is a case where a single heterodyne system is adopted for the receiving system. First, to explain briefly from the transmitting system side, the signal is converted into an electrical signal via the microphone 24, and an appropriate low frequency signal is transmitted. The low frequency input signal for transmission amplified via the amplifier (AF amplifier) 23 is applied to the modulation circuit 22 which modulates the local oscillation frequency FLI generated by the local oscillation circuit 13 whose frequency is stabilized by the crystal oscillator XI. The transmission frequency FT modulated thereby is radiated from the antenna 10, which may be configured as a transmitting/receiving antenna, though it may be separate for transmitting and receiving, via a suitable high frequency amplification circuit (RF amplifier for Tx) 21.

For this reason, the local oscillation circuit 13 is also used as a generation circuit for the transmission carrier frequency FA, and since the transmission carrier frequency FA is equal to the local oscillation frequency FLI, the transmission carrier frequency generation circuit and the local oscillation circuit Compared to the case where each is prepared separately, the number of sets of crystal oscillators and accompanying PLL circuits is definitely reduced by one.

On the other hand, in terms of reception, the reception frequency FR input from the antenna IO is also connected to an appropriate high frequency amplifier (RX
RF amplifier)! 1, the signal is input to the mixer 12, where the beat is taken from the local oscillation frequency FLI generated by the local oscillation circuit 13, and the intermediate frequency F1 is obtained.

Since we are assuming a single heterodyne here,
This intermediate frequency FErI becomes the final fixed frequency to be applied to the detector δ.

However, as mentioned above, the local oscillation circuit 13
transmits the local oscillation frequency FLI emitted by the carrier frequency F
As a result of using it as a sidetone component, the local oscillation frequency FLI on the receiving system side contains a low-frequency input signal that modulates the transmitting carrier frequency on the transmitting system side as a sidetone component.
Therefore, as a result of this and the beat, mixer 1
Naturally, this sidetone component is also included in the intermediate frequency FIIFI appearing in the output of 2.

Therefore, in the first illustrated embodiment constructed according to the present invention, the discriminator coil attached to the detector 16, which is an FM demodulation circuit of intermediate frequency F1□ including the sidetone component, has the following characteristics: On the transmission system side, a low frequency input signal from the microphone 24, which is information to be transmitted, is applied via a varicap VC.

In this way, the resonant frequency of the resonant circuit including the discriminator coil L1 can be modulated according to the low frequency input signal, so the sidetone component on the intermediate frequency F, □ can be modulated by this detector. 16 can be offset.

Further, the modulation degree adjustment at this time can be accomplished, for example, by a simple compensation circuit 3o that adjusts the level of the AF amplifier output that amplifies the microphone input on the transmission system side. In addition to the potentiometer circuit, the transmission system modulation circuit 22 and the discriminator circuit.
Even if it is necessary to prevent mutual interference between coils, this can be achieved by adding a simple buffer amplifier.

However, in the case of the illustrated embodiment, the detector 16 is a detector IC that has recently been integrated and commercially available.
16 is assumed to be used.

Such detector ICs do not only have an FM demodulation function, but also include an intermediate frequency amplification stage at the front stage and a low frequency amplification driver stage at the rear stage, but in any case, they do not have a discriminator function.・Despite the size of the coil, it is usually installed externally.

However, this is rather advantageous when implementing the invention. This is because the varicap VC can be attached outside the IC.

For example, the detector I intended for use in the illustrated embodiment
At C, discriminator coil L.

is a type that is inserted in series between the power supply Vcc (.5V) and the IC-dedicated terminal.

Therefore, the varicap VC provided according to the present invention is inserted in series with the auxiliary capacitor between the IC side end of the discriminator coil Ll and the ground, and connected to the connection point between the varicap VC and the auxiliary capacitor. On the other hand, the low frequency output of the transmitting side AF amplifier 23 is applied via the above-described compensation circuit 30. This proves that, in practice, the additional components required to implement the invention are few in number and nothing special in kind.

Of course, depending on the actual commercially available type of detector 16 used, in order to modulate the resonant frequency of the resonant circuit including the discriminator coil Ll in the direction of canceling the sidetone component riding on the intermediate frequency F, Specific points suitable for actually connecting the varicap VC can be changed as appropriate, and such design changes are extremely easy for those skilled in the art.

In any case, according to the present invention, the low frequency output signal demodulated with the sidetone component removed is sent to an electro-acoustic converter as an information reproducing terminal via a suitable AF amplifier 17. Generally, it is radiated from the speaker 18 as an audible information signal.

However, the microphone 24 and the speaker 18 are only examples of the most common input/output means for low-frequency signals, and other low-frequency signal generation means and low-frequency signal processing means can be used to A transmitting/receiving system in place of the speaker 18 is also conceivable. In addition, when the antenna IO is generally configured as a transmitting/receiving antenna, a means for splitting or combining the transmitting frequency FT and the receiving frequency FR is adopted, but this is also not directly related to the present invention. , illustration is omitted.

Furthermore, in the case of the illustrated embodiment, the case where a single heterodyne system is adopted on the receiving system side has been described, but based on the principle of the present invention, it is also applicable to a receiving system that adopts a double heterodyne system. be able to. This is because a sidetone component similar to that of the first intermediate frequency Fart can be recognized at the second intermediate frequency FIP2, and this can be similarly removed by the detector 16 as long as the present invention is followed.

[Effects] As described above, according to the present invention, by configuring a crystal oscillator and a PLL circuit that are used for both transmission and reception, the number of parts can be reduced,
By simplifying the circuit, downsizing the device, and lowering the cost, it is possible to rationally avoid the inconvenience of sidetone generation associated with this.

In particular, this can be avoided by applying a low-frequency input signal to the discriminator coil attached to the detector via a varicap, as seen in the conventional example mentioned at the beginning. There are no drawbacks such as the heterodyne system employed in the receiving system being limited to the double heterodyne system or being affected by the circuit characteristics of the downstream stage of the detector.

Moreover, the circuit configuration for realizing the present invention is extremely simple, and there are no restrictions on installing it in a product.In the end, it is possible to provide a wireless transmitting/receiving device that is highly flexible, has good performance, and is inexpensive. can.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of a wireless transmitting/receiving device constructed according to the present invention. FIG. 2 is a schematic configuration diagram of a typical example of a conventional wireless transmitting/receiving device that is designed to reduce the number of crystal oscillators when a super-heterodyne system is adopted for the receiving system. FIG. 3 is a schematic configuration diagram of a typical example of a conventional wireless transmitting/receiving device that is designed to reduce the number of crystal oscillators even when a single heterodyne system is adopted for the receiving system. In the figure, lO is an antenna, 12 is a mixer, 13 is a local oscillation/transmission carrier oscillation circuit, 16 is a detector, 22 is a modulation circuit, 30 is a compensation circuit, X, , X is a crystal oscillator, and L is a disc limiter. Noeta coil, VC is varicap. Figure Δk, j′tsu

Claims (3)

[Claims] (1) It has a receiving system and a transmitting system, and the receiving system includes a mixer means that takes the beat of the receiving frequency and the local oscillation frequency and finally generates a fixed intermediate frequency, and a mixer means that takes the beat of the receiving frequency and the local oscillation frequency, and The transmitting system includes a detector for demodulating, and a detector for demodulating.
In a radio transmitter/receiver including a modulation circuit that modulates a transmission carrier frequency with a low frequency input signal; while providing the modulated transmission carrier frequency to the mixer means as a local oscillation frequency of the reception system; A varicap is connected to a discriminator coil assembled to the detector; the low frequency input signal modulating the transmission carrier frequency is applied via the varicap, and a resonant circuit including the discriminator coil is connected. A wireless transmitting/receiving device characterized in that a sidetone component due to the low frequency input signal mixed in the intermediate frequency is canceled by modulating the resonance frequency of the wireless transmitter/receiver. 2. The apparatus according to claim 1, wherein: (2) the mixer means is a single mixer in a single heterodyne receiving system. (3) The mixer means includes first and second mixers in a double heterodyne receiving system, the local oscillation frequency is applied to the first mixer, and the final fixed intermediate frequency is output from the second mixer. The device according to claim 1, characterized in that: