JP2931445B2 - Interference Modulator for Radio Transmitter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a transmission frequency between a plurality of transmitters corresponding to the number of slave units built in a master unit when a call between slave units in a cordless telephone system is performed by relaying a subscriber telephone equipped with a radio unit. The present invention relates to a device that suppresses a modulation interference wave caused by mutual sneaking around.

[0002]

2. Description of the Related Art In a cordless telephone system comprising a plurality of portable radio units provided with a calling function capable of moving within a certain distance, using a subscriber telephone with a radio unit connected to a telephone line as a base unit. Since the communication between the slaves is performed by relaying the master, the master has a built-in transmitter and receiver corresponding to the number of slaves.

By the way, as long as the output frequency of each transmitter wraps around from one side to the other and the non-linear transistor provided in each RF stage is used as an amplifier, it is possible to avoid the occurrence of speech disturbance due to intermodulation. I can't. Normally, the transmission and reception channels of a radio are divided at a fixed frequency interval, and occur in a voltage-controlled oscillator that transmits the transmission frequency of a transmitter in order to suppress the level of an interfering wave caused by intermodulation to a certain value or less. There is known a circuit configuration as shown in FIG. 2 in which transistor amplifiers are connected in multiple stages to cope with the intermodulation level.

In FIG. 2, four stages of cascade-connected transistor amplifiers 11 to 14, 21 to 24 are connected to voltage-controlled oscillators 10 and 20, which are transmission frequency sources of the respective transmitters.
Are connected, and isolators 15 and 16 each composed of a non-reciprocal transmission circuit element are provided. Each transmitter is connected to the antenna 1 via the coupler 2. However, in the above-mentioned conventional circuit configuration, a so-called “one transmitter”
Since the reverse attenuation cannot be sufficiently obtained, the output frequency of the other transmitter reaches the voltage-controlled oscillator, but this voltage-controlled oscillator has a tuning function for variably controlling the oscillation frequency. The difference between the oscillation frequency of the transmitter from one to the other and the oscillation frequency of the other transmitter Δ
From the relationship between f and the level of the interfering wave caused by intermodulation, it seems at first glance that the further away from the frequency, the greater the amount of attenuation is obtained, but when trying to lower the level of the interfering wave due to intermodulation, It will increase the interval between the transmission channels of each of the multiple transmitters,
As a result, the use efficiency of the channel is significantly reduced, and in an area where a large number of cordless telephones are installed, a call failure may be caused.

If the number of transistor amplifiers is increased in the RF stage of the transmitter to reduce the level of the reverse input to the voltage controlled oscillator in order to increase the channel utilization efficiency, the internal space of the radio becomes insufficient and the cost increases. The drawback is that the current consumption increases and the current consumption increases.

[0006]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to reduce an interference wave caused by an intermodulation caused by a wraparound of a transmission frequency from one of a plurality of transmitters to the other. With the amount of reverse attenuation that is suppressed to
The purpose is to provide sufficient transmission power to the antenna.

[0007]

SUMMARY OF THE INVENTION The present invention provides a pi-type configuration between multiple stages of transistor amplifiers cascaded to the RF stage of a voltage controlled oscillator having a tuning function for each of a plurality of transmitters to transmit a transmission frequency. At least two or more stages of attenuators with resistors are interposed to suppress the level of the other transmission frequency due to the sneak path between the transmitters without increasing the frequency interval between the channels of the plurality of transmitters,
The purpose is to suppress the level of an interfering wave generated by the intermodulation.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention (in the case of two slave units) will be described in detail with reference to FIG. First, in FIG. 2, a voltage controlled oscillator (VCO ₁ or VC
O ₂ ) 10 is −10 dB, the reverse attenuation of the transistor amplifier, that is, the level from the collector to the base is 15 dB
And the gain of the four-stage transistor amplifier is 15 for 15
B and 13 are 11 dB and 14 are 11 dB, and the output of the last stage is a minimum of +20 dBm. When there is no attenuator 31 or 32 having a π-type resistor, the total attenuation in the reverse direction is 20 dB for the coupler and 20 dB for the isolator 15.
B, the transistor amplifiers 11, 12, 13, 14 are 15
Since × 4 = 60 dB, the total is almost 100 dB.

If the output of the last-stage transistor amplifier 10 of the other transmitter is +20 dBm, the transmission frequency of the one transmitter sneaking into the voltage-controlled oscillator 10 in the reverse direction reaches +20 dBm-100 dB = 80 dBm. As can be seen from FIG. 3, the intermodulation level generated at the output side of one of the voltage controlled oscillators is the difference between the intermodulation level for the reverse input frequency Δf of the voltage controlled oscillator and the reverse input level to the voltage controlled oscillator. Looking, Δf is 12.
-65.8d at 5KHz (corresponding to one channel interval)
Bm, -72.6 dB at 25 KHz (corresponding to two channels), -76.0 dBm at 37.5 KHz (corresponding to three channels), -77.6 at 50 KHz
It has been demonstrated to be dBm.

[0010] Therefore, in order to suppress the intermodulation level to a level that does not disturb as an interfering wave, it is suggested that the intermodulation level occurring in the voltage-controlled oscillator for transmitting the transmission frequency of each transmitter should be -90 dB or less. And
Therefore, according to the conventional circuit, the interval between the channel frequencies must be increased.

Therefore, in the present invention, as shown in FIG. 1, the gain of the cascaded multi-stage transistor amplifier is selected to the maximum, and the stages of the transistor amplifier are selected so that the maximum attenuation of the output of the final-stage transistor amplifier is +20 dB or more. When at least two or more attenuators each having a π-type resistor with a coupling capacitor interposed therebetween are inserted, the gain from the output terminal of the voltage-controlled oscillator to the output of the last-stage transistor amplifier is +20 dB − (− 10 dB) = 30 dB. Becomes
In this embodiment, the total gain of the four-stage transistor amplifier is 1
Since 5 dB + 15 dB + 11 dB + 11 dB = 52 dB, a predetermined output and level can be obtained by interposing an attenuator of 52 dB-30 dB = 22 dB.

[0012] Thus, the reverse attenuation from one transmitter to the other transmitter was conventionally 100 dB, but according to the circuit of the present invention, it becomes 122 dB, and the level of intermodulation occurring in the voltage controlled oscillator is reduced. 22dB for each transmitter
As shown in FIG. 3, the conventional circuit was −72.6 dB with respect to the intermodulation level when Δf was 25 KHz. However, in the circuit of the present invention, −72 + (− 22) = − 94.6 dB. It can be seen that a modulation level of -90 dB or less has been achieved. Therefore, the intervals between the transmission channels of the transmitters are not affected by interference only by separating two channels, and it is not necessary to increase the intervals between the transmission channels of the plurality of transmitters.

[0013]

The final stage of the multistage cascaded transistor amplifier connected to the RF stage of the transmitter is based on the amount of reverse attenuation of the disturbance wave to the voltage-controlled oscillator which is stored in each of the plurality of transmitters and transmits the transmission frequency. In consideration of the total gain up to the stage, only by inserting an attenuator configured as a resistor WO type between the stages of the transistor amplifier, it is possible to effectively and inter-modulate the intermodulation interference wave caused by the sneak in the transmission frequency between the transmitters. It can be easily attenuated, and the level of the interfering wave itself due to intermodulation is attenuated even if the interval frequency of the transmission channel is narrowed by suppressing the wraparound level of the transmitter output frequency from the other side below a certain value. Therefore, the present invention contributes to efficient and trouble-free use of the communication channel even in an area where the cordless telephone is frequently used. In addition, the transistor amplifiers 11, 12, 21, and 22 have a buffer function, so that the current is suppressed. Even if the intermodulation characteristics are not excellent, the attenuator is inserted between the stages of the transistor amplifiers. Can be improved, and the intermodulation level generated by the voltage controlled oscillator can be reduced to the same level.

[0014]

[Brief description of the drawings]

FIG. 1 is a block diagram of a main part of a transmitter RF stage for suppressing intermodulation due to a transmission frequency according to the present invention.

FIG. 2 shows a conventional RF of a transmitter having an intermodulation suppression function.
FIG. 2 is a block diagram of a main part of a step.

FIG. 3 is a graph showing a relationship between a reverse input frequency Δf to a voltage controlled oscillator and a difference between an intermodulation level and a reverse input level of the voltage controlled oscillator.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Antenna 2 Coupler 10, 20 Voltage controlled oscillator 11, 12, 13, 14 Transistor amplifier 21 22, 23, 24 Transistor amplifier 31, 32, 41, 42 Attenuator

Claims (1)

(57) [Claims] In a cordless telephone system in which a plurality of mobile terminals communicate with each other by relaying a telephone set with a radio connected to a telephone line, a plurality of transmitters corresponding to the number of the above-mentioned terminals are provided. A multi-stage cascaded transistor amplifier for amplifying a transmission frequency from a voltage-controlled oscillator having a tuning function is provided. Each of the transistor amplifiers is configured to have a maximum gain, and the stages of the transistor amplifier are considered in consideration of an overall gain. At least two stages of attenuators, each of which has a π-type resistor with a coupling capacitor between them, are inserted in at least two stages to reduce inter-modulation interference waves without expanding the channel spacing frequency of each of the multiple transmitters. A device for suppressing interfering waves due to intermodulation of a wireless transmitter.