JPH04373317A - Portable digital telephone set - Google Patents

Abstract

PURPOSE:To obtain a telephone set reducing the insertion loss of the switching circuit of high frequency signals without operating transmission signals to a transmission system as jamming signals in the case of transmission by switching a reception system preamplifier and a transmission system power amplifier in the cases of reception and transmission, turning the transmission side to a high impedance in the case of reception observing it from the transmission/ reception connecting point of an antenna, and turning the reception side to the high impedance in the case of transmission. CONSTITUTION:Both a preamplifier 2 and a power amplifier 6 use an NPN transistor in an emitter installation system, a transistor for control is interposed between the collectors of both transistors and a power source B+. According to a control signal from a CPU, the two transistors for control are alternately conducted. In the case of reception, a phase characteristic is changed so that the impedance of the transmission side observed from a transmission/reception connecting point 7 of an antenna 1 can be made high and in the case of transmission, the phase characteristic is changed so that the impedance of the reception side observed from the transmission/reception connecting point 7 can be made high.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to mobile communication equipment, particularly digital car telephones and portable telephones.

0002

BACKGROUND OF THE INVENTION In recent years, mobile communication devices, particularly car telephones and mobile phones, have become widespread, and it is said that they will face a frequency shortage in the near future. Under these circumstances, as a countermeasure, the introduction of digital systems using quasi-microwave bands is being considered for current analog car phones, mobile phones, and even cordless phones.

That is, in the current analog system, one terminal uses one frequency exclusively (FDMA: Freque
ncy DivisionMultipulAcce
ss), as the number of users increases, there will be a shortage of frequencies. Therefore, a method of dividing one frequency by several people in time (TDMA: Time Division Ma
Digital mobile phones attempt to make effective use of frequencies.

Now, in the current analog system, calls are made using different frequencies for transmission and reception (FDD: Frequency
(TDD: Time Divisi), which uses the same frequency for transmission and reception by digitizing
on Duplex). Such digital systems are currently being planned for use in Japan as a core technology for future mobile telephone communications, and are also gradually being put into practical use in Europe. And this TDD
As an example of this method, a circuit configuration as shown in FIG. 4, for example, has been proposed.

In this circuit, a radio wave received by an antenna 1 is amplified by a preamplifier 2, and then amplified by a first local oscillator 5.
After the frequency is converted by the mixer circuit 3, the IF amplifier 4
The signal is amplified and then demodulated. On the other hand, when transmitting, the oscillation frequency of the first local oscillator 5 directly becomes the transmission frequency, and the transmission wave is amplified by the power amplifier 6 for transmission and then transmitted from the antenna 1. The first local oscillator is a PLL (Phase Locked Loo).
p) It uses a circuit to lock the frequency and is controlled by the CPU to change the frequency between transmitting and receiving. As described above, in the method currently being considered, switching between transmitting and receiving operations is achieved by changing the frequency of the first local oscillator, and at the same time, it reduces interference between transmitting and receiving caused by the fact that the transmitting and receiving frequencies are the same frequency. For this purpose, a transmit/receive signal switching circuit 8 is provided at the transmit/receive connection point of the antenna, and the circuit is switched between transmitting and receiving signals.

[0006]

[Problem to be Solved by the Invention] However, with the above configuration, when switching between transmission and reception, the switching circuit in the high frequency quasi-microwave band cannot sufficiently attenuate the signal, resulting in poor isolation characteristics. to degrade. Therefore, during transmission, the transmitted signal becomes a signal that interferes with the receiving system. Furthermore, since insertion loss increases in the high-frequency signal switching circuit, reception sensitivity deteriorates in the reception system, and a large amount of transmission power is required in the transmission system, resulting in deterioration of transmission efficiency.

[0007] In view of the above points, the present invention has been made for the purpose of providing a digital mobile phone that can sufficiently cope with future frequency shortages and has good transmission efficiency.

[0008]

[Means for Solving the Problems] In order to achieve the above object, in the present invention, a receiving system includes a preamplifier that amplifies a high frequency signal received from an antenna, a receiving system mixer circuit that converts the frequency of the amplified signal, A digital mobile phone having a local oscillator for performing the frequency conversion and an amplifier for amplifying the frequency-converted IF frequency, and a transmission system having a transmission amplifier for amplifying a high-frequency transmission signal and transmitting it from an antenna. In this method, the transmitting and receiving signals are switched by turning on and off the amplifier operations of the receiving system preamplifier and the transmitting system amplifier at the time of receiving and at the time of transmitting, and at the same time, at the transmitting and receiving connection point of the antenna, the impedance of the transmitting side is changed at the time of receiving. To make it high impedance,
The digital mobile phone is characterized in that the impedance at the transmission/reception connection point is set so that the impedance on the receiving side becomes high impedance during transmission.

[0009]

[Operation] With the above configuration, it is possible to switch the transmitter/receiver circuit by switching the amplifier and switching the impedance.

0010

Embodiments Hereinafter, embodiments of the present invention will be explained using FIGS. 1 to 3. FIG. 1 is a diagram showing its configuration. The main structure of the mobile phone of this embodiment, the functions of each component, etc. are the same as those conventionally considered as shown in FIG. Therefore, only the parts related to the present invention will be explained below, and explanations of the modulation circuit, demodulation circuit, data processing section, etc. will be omitted.

FIG. 2 is a circuit diagram showing on/off switching of the preamplifier 2 and the power amplifier 6. Here, both the preamplifier 2 and the power amplifier 6 include NPN transistors Tr1,
Tr2 is used in an emitter installation method. Control transistors Tr3 and Tr4 are interposed between the collectors of both transistors Tr1 and Tr2 and the power supply +B. A control signal is applied from the CPU to the bases of both control transistors Tr3 and Tr4. Here, one of the control transistors Tr3 is a PNP type, and the other is an NP type.
Since it is an N type, the two control transistors Tr3 and Tr4 are selectively turned on by a control signal from the CPU. That is, when the control signal is "H", the NPN type control transistor is conductive and the PNP type control transistor Tr3 is non-conductive, while when the control signal is "L", the PNP type control transistor is conductive. Tr3 conducts and becomes NPN
The type control transistor Tr3 becomes non-conductive. When the control transistor Tr3 or Tr4 becomes conductive, a +B voltage is applied to the transistor Tr1 or Tr2, which starts the desired preamplification or power amplification operation.

Furthermore, the input impedance of the receiving system preamplifier 2 is in a matching state with the antenna 1 during reception, but during transmission, the impedance is sufficiently mismatched due to the off state of the amplifier operation.
The output impedance of the antenna 1 is also matched with the antenna 1 during transmission, but the impedance is configured to be sufficiently mismatched during reception due to the off-state of the amplifier. Therefore, in this embodiment, during reception, the phase characteristics are changed so that the impedance on the transmitting side seen from the transmitting/receiving connection point 7 of the antenna becomes high impedance, and during transmission, the impedance on the receiving side seen from the transmitting/receiving connecting point 7 becomes high impedance. The phase characteristics are changed so as to change the impedance. The Smith chart in Figure 3 (Smith Cha
rt) shows the S11 characteristic of the S parameter, which is the input impedance of the receiving system preamplifier 2. Based on this diagram,
I will explain the changes. Figure 3-A is the receiving system amplifier 2
is the S11 characteristic during operation, and is the impedance seen from point a in FIG. 2 in the direction of the three arrows. S11 is matched to approximately 50Ω. However, at the time of transmission, the operation is turned off by a control signal from the CPU, so the S11 characteristic becomes largely mismatched as shown in FIG. 3-B. It is configured to change the phase characteristics so that this input impedance becomes a relatively high impedance. Therefore, for example, in a strip line with a characteristic impedance of 50Ω, the impedance can be set high at a location separated by a length l. Point b in FIG. 3-B is a point where the phase of the impedance at point a is changed by L. The impedance at this point is extremely high, so by setting this point to be the transmitting/receiving connection point 7 in Figure 2, the impedance when looking at the receiving side from this point in the direction of the three arrows as shown in Figure 2 during transmission. Since it can be set to a high value, it is possible to efficiently transmit the transmission signal from the antenna (that is, the design values of various components such as the strip line of the receiving system are determined so as to achieve this). On the other hand, during reception, the impedance b' when viewed from the transmission/reception connection point 7 in the direction of the arrow shown in FIG. The transmitting/receiving connection point is located at a distance of L'.

[0013]

Effects of the Invention: Since no transmission/reception switching circuit is required, there is no insertion loss of the switching circuit, and there is no deterioration in receiving sensitivity in the receiving system due to increased insertion loss. Furthermore, since transmission power can be directly output in the transmission system, transmission efficiency can be improved. Furthermore, at the time of transmission, the impedance on the receiving side at the transmitting/receiving connection point is set high, and the operation of the receiving system amplifier is turned off, so that the transmitting signal does not occur as an interference signal in the receiving system.

[0014] As a result, it becomes possible to provide an efficient digital mobile phone that can cope with future frequency shortages.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of a digital mobile phone according to the present invention.

FIG. 2 is a circuit diagram of a switching section in the above embodiment.

[Fig. 3] Input S-parameters (S1
1) Characteristic diagram.

FIG. 4 is an example of a block diagram of a TDD digital mobile phone according to the prior art.

[Explanation of symbols]

1 Antenna 2. Receiving system preamplifier 3 Receiving mixer circuit 4 Receiving system IF amplifier 5 First local oscillator 6 Transmission system power amplifier 7 Transmission/reception connection point 8 Switching circuit

Claims (1)

[Claims] Claim 1: The receiving system includes a preamplifier that amplifies the high frequency signal received from the antenna, a receiving system mixer circuit that converts the frequency of the amplified signal, a local oscillator for performing the frequency conversion, and an IF after the frequency conversion. In a digital mobile phone, the receiving system preamplifier and the transmitting system amplifier are connected at the time of reception in a digital mobile phone having a transmitting amplifier that amplifies the high frequency transmission signal and transmits it from the antenna in the transmitting system. At the time of transmission, the transmitting and receiving signals are switched by turning on and off the amplifier operation, and at the same time, at the transmitting and receiving connection point of the antenna, the impedance on the transmitting side becomes high impedance at the time of receiving.
A digital mobile phone characterized in that the impedance at the transmission/reception connection point is set so that the impedance on the receiving side becomes high impedance during transmission.