JP2012114547A - Transmission circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transmission circuit capable of detecting a reflection signal from an antenna with an isolator without need for a directional coupler and capable of being automatically adjusted to a preferable transmission state.SOLUTION: The transmission circuit includes: an isolator 20 having a terminal resistance R; RF signal detection means (a detection diode D) electrically connected with the terminal resistance R; adjustment means (a switching element Sw) for switching antenna characteristics; and control means 30 for changing the switching element Sw by outputting a control signal corresponding to a magnitude of a detection signal by the detection diode D.

Description

  The present invention relates to a transmission circuit, and more particularly to a transmission circuit incorporated in a portable wireless communication terminal.

  Conventionally, a transmission signal from a power amplifier is output to an antenna via an isolator in a transmission circuit of a portable wireless communication terminal. The isolator has a characteristic (irreversible) in which a signal is transmitted only in a predetermined direction and is not transmitted in the reverse direction.

  By the way, in the portable wireless communication terminal, the input impedance of the antenna may change due to a change in usage environment (for example, a metal material is close to the terminal). In this case, impedance mismatch occurs and the transmission signal is reflected from the antenna, so that the radiation output from the antenna is reduced. In order to correct the drop in the transmission signal, there is a method for detecting a part of the transmission signal and feeding it back to the power amplifier to increase the transmission output. However, since the transmission signal reflected by the antenna is consumed by the isolator and there is no change in the transmission signal, this method cannot detect that the radiation output from the antenna has decreased.

  In order to detect a transmission signal reflected by an antenna, Patent Documents 1 and 2 describe a circuit configuration in which a directional coupler is added between an antenna and an isolator. However, this requires an expensive directional coupler having high directivity in order to distinguish the forward direction from the reverse direction, which is not practical in terms of cost.

JP 2002-57511 A JP 2000-341143 A

  Therefore, an object of the present invention is to provide a transmission circuit that can detect a reflected signal from an antenna by an isolator without requiring an expensive directional coupler, and can automatically adjust to a preferable transmission state.

A transmission circuit according to one embodiment of the present invention is
An isolator having a termination resistor;
RF signal detection means electrically connected to the termination resistor;
Adjustment means for switching antenna characteristics;
Control means for changing the adjustment means by outputting a control signal according to the magnitude of the detection signal by the RF signal detection means;
It is provided with.

  The isolator provided in the transmission circuit outputs a transmission signal to the antenna in the forward direction, and the reverse signal is not transmitted because it is consumed as heat by the terminating resistor. The reflected signal from the antenna is detected by the RF signal detection means, and when the magnitude of the detection signal increases, the control means changes the adjustment means to switch the antenna characteristics. For example, when a main antenna and a sub antenna are installed, the main antenna is switched to the sub antenna or vice versa. Moreover, the characteristic is switched by changing the impedance of one antenna. Thereby, the radiation output from the antenna can be stabilized without using an expensive directional coupler.

  According to the present invention, a reflected signal from an antenna can be detected by an isolator without requiring an expensive directional coupler, and can be automatically adjusted to a preferable transmission state.

FIG. 3 is an equivalent circuit diagram illustrating a transmission circuit according to the first embodiment. FIG. 6 is an equivalent circuit diagram illustrating a transmission circuit according to a second embodiment.

  Embodiments of a transmission circuit according to the present invention will be described below with reference to the accompanying drawings. In addition, in each figure, the same code | symbol is attached | subjected about the same member and part, and the overlapping description is abbreviate | omitted.

(See the first embodiment, FIG. 1)
The transmission circuit according to the first embodiment, as shown in FIG. 1, transmits a transmission signal to either the main antenna Am or the sub-antenna As, and includes a power amplifier PA, an impedance matching circuit 10, an isolator 20, A duplexer Dup and adjustment means (switching element Sw) are provided, and further, RF signal detection means (detection diode D) incorporated in the isolator 20 and a control circuit 30 are provided.

  The power amplifier PA amplifies the transmission signal of the baseband IC. The impedance matching circuit 10 converts the impedance to 50Ω, and is formed as a resonance circuit including an inductor L11 and a capacitor C11. The inductor L11 is connected in series between the output terminal 41 of the power amplifier PA and the input terminal 25 of the isolator 20. One end of the capacitor C11 is connected between one end of the inductor L11 and the input terminal 25 of the isolator 20, and the other end is grounded.

  The duplexer Dup transmits the transmission signal to the antennas Am and As and transmits the reception signal to a reception circuit (not shown). The switching element Sw is connected to the input / output terminal 45 of the duplexer Dup, and switches between the main antenna Am and the sub-antenna As for transmission or reception.

  The isolator 20 is a lumped constant type two-port type, and includes a ferrite 21 to which a DC magnetic field is applied by a permanent magnet (not shown), and a first center electrode 22 (L1) arranged to intersect the ferrite 21 in an insulated state. ) And a second central electrode 23 (L2). The first center electrode 22 has one end connected to the input port P1 and the other end connected to the output port P2. The second center electrode 23 has one end connected to the output port P2 and the other end connected to the ground port P3. A termination resistor R is connected in parallel with the first center electrode 22 between the input port P1 and the output port P2, and a first matching capacitor C1 is connected between the input port P1 and the output port P2. A second matching capacitor C2 is connected between P2 and the ground port P3. The first port P1 is connected to the input terminal 25, and the second port P2 is connected to the output terminal 26.

  The detection diode D is connected in parallel with the termination resistor R between the input port P1 and the output port P2. The control circuit 30 detects the detection signal of the detection diode D, drives the switching element Sw, and switches the antennas Am and As.

  In this isolator 20, during a forward operation in which a high-frequency signal (transmission signal) flows from the input terminal 25 to the output terminal 26, a large high-frequency current flows through the second center electrode 23, and almost all the high-frequency current flows through the termination resistor R and the capacitor C1. Does not flow (current does not flow through the detection diode D), so that the transmission signal is transmitted with a small insertion loss. On the other hand, when a high-frequency current is input from the output terminal 26, the high-frequency current is attenuated by the parallel resonance circuit formed by the first center electrode 22 and the capacitor C1, and is consumed as heat by the terminating resistor R. Is done. The amount of attenuation can be adjusted by the impedance of the terminating resistor R.

  This transmission circuit is used by being incorporated in a portable wireless communication terminal. When a metal material approaches the terminal at the time of use and the impedance of the antennas Am and As changes, the transmission signal is reflected from the antennas Am and As, and the radiation output decreases. When the reflected signals from the antennas Am and As increase, the reflected signals are detected by the control circuit 30 as the output value (DC voltage) of the detection diode D. Therefore, when the reflected signal from the currently used antenna (for example, the main antenna Am) increases by a certain amount, the control circuit 30 operates the switching element Sw to switch the used antenna from the main antenna Am to the sub antenna As. As a result, the communication state is adjusted to a preferable one.

(See the second embodiment, FIG. 2)
As shown in FIG. 2, the transmission circuit according to the second embodiment basically has the same configuration as that of the first embodiment, except that one antenna A is used, and the antenna characteristics are This is in that a variable capacitance device 35 is used in place of the switching element Sw as the adjustment means for switching. The variable capacitance device 35 is formed as a resonance circuit including an inductor L21 and a variable capacitance capacitor C21. The inductor L21 is connected in series between the input / output terminal 45 of the duplexer Dup and the antenna A. One end of the variable capacitor C21 is connected between one end of the inductor L21 and the antenna A, and the other end is grounded.

  The operation of the isolator 20 is as described in the first embodiment. When the input impedance of the antenna A changes in the vicinity of a metal material, the increase in the reflected signal from the antenna A is controlled as the output value of the detection diode D. Detected by the circuit 30, the capacitance of the variable capacitance capacitor C21 is changed. As a result, the input impedance of the antenna A is changed, and loss due to impedance mismatch can be reduced.

  The capacitance variable capacitor C21 may have either a capacitance value that can be changed stepwise or a capacitance value that can be changed steplessly.

(Other examples)
The transmission circuit according to the present invention is not limited to the above embodiment, and can be variously modified within the scope of the gist thereof.

  For example, the RF signal detection means can use various detection circuits other than the detection diode D. Even in the adjusting means, elements and circuits other than the switching element Sw and the variable capacitance capacitor C21 can be used. In addition, as long as the isolator 20 itself has a termination resistor R, it is possible to use various configurations.

  As described above, the present invention is useful for a transmission circuit incorporated in a portable wireless communication terminal and the like, and particularly excellent in that a reflected signal from an antenna can be detected by an isolator and automatically adjusted to a preferable transmission state. Yes.

DESCRIPTION OF SYMBOLS 20 ... Isolator 21 ... Ferrite 22 ... 1st center electrode 23 ... 2nd center electrode 30 ... Control circuit 35 ... Capacitance variable device P1 ... Input port P2 ... Output port P3 ... Ground port C1, C2 ... Capacitor for matching R ... Termination resistance D ... Detection diode PA ... Power amplifier Sw ... Switching element A, Am, As ... Antenna

Claims (5)

An isolator having a termination resistor;
RF signal detection means electrically connected to the termination resistor;
Adjustment means for switching antenna characteristics;
Control means for changing the adjustment means by outputting a control signal according to the magnitude of the detection signal by the RF signal detection means;
A transmission circuit comprising:   2. The transmission circuit according to claim 1, wherein the RF signal detection means is a detection diode.   The transmission circuit according to claim 1, wherein the adjustment unit is a switching element that switches connection to two antennas.   The transmission circuit according to claim 1, wherein the adjustment unit is a variable capacitance device that changes the impedance of one antenna. The isolator is
With permanent magnets,
A ferrite to which a DC magnetic field is applied by the permanent magnet;
A first center electrode and a second center electrode, which are arranged to intersect the ferrite in an insulated state;
With
The first center electrode has one end electrically connected to the input port and the other end electrically connected to the output port;
The second center electrode has one end electrically connected to the output port and the other end electrically connected to the ground port.
A first matching capacitor is electrically connected between the input port and the output port;
A second matching capacitor is electrically connected between the output port and the ground port;
The termination resistor is electrically connected between the input port and the output port;
The transmission circuit according to any one of claims 1 to 4, wherein:

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