JPH09162662A - Variable gain circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the reception sensitivity of the variable gain circuit by avoiding a loss caused by an input signal that passes through a switch circuit used to select a signal path. SOLUTION: A series connection circuit consisting of 1/4 wavelength transmission lines 21, 22 is connected in parallel with an amplifier 20, and a single pole single throw(SPST) switch S2 is inserted between a connecting point of the 1/4 wavelength transmission lines 21, 22 and ground. Furthermore, an SPST switch S1 is inserted into a power supply line of a power supply section 24 and the amplifier 20 similarly. When amplification of an input signal is required, a switch control section 23 closes both the switches S1, S2 to form a path for the input signal to be fed to the amplifier 20 from which an amplified output is obtained, and when no signal amplification is required, the switch control section 23 opens both the switches S1, S2 to allow the input signal to pass through the series connection circuit consisting of the 1/4 wavelength transmission lines 21, 22 as an output signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable gain circuit, and in particular, it is suitable for application to a variable gain circuit provided in a transmission device in which transmission power control is performed and a reception device in which the reception power level fluctuates. .

[0002]

2. Description of the Related Art In mobile communication, for example, generally, a signal of a reception / transmission signal is always received due to a change in distance between a mobile station, which is a mobile communication terminal, and a base station, and fading in a transmission line. The intensity varies. Therefore,
For example, on the mobile station side, a variable gain circuit capable of amplifying or attenuating the received signal according to the intensity of the received signal is provided in the RF signal processing stage or the IF signal processing stage, whereby the signal strength of The fluctuation is absorbed and the received signal is set to a substantially constant level and then supplied to a demodulator in the subsequent stage.

FIG. 9 is a block diagram showing a configuration example of the variable gain circuit. In this case, the description will be made assuming that the mobile communication terminal is provided with the gain adjustment for the RF signal. The variable gain circuit shown in this figure includes switches S10 and S11 and a switch controller 2
3 and an amplifier 20. Switch S
10 and S11 have terminals TM1 and TM2 or TM, respectively.
3 is selectively switched, and the switching control is performed in a linked manner by a control signal supplied from a switch control unit 23 described later. The switch unit 23 outputs a switching control signal to the switches S10 and S11 based on the level information of the received signal supplied from the baseband signal processing unit of the mobile communication terminal (not shown). The amplifier 20 is composed of an amplifier capable of amplifying a high frequency signal such as an RF signal and has a predetermined amplification factor.

The received wave of the RF signal input from the input terminal T1 is supplied to the terminal TM1 of the switch S10.
The terminal TM2 of the switch S10 is connected to the input of the amplifier 20, and the terminal TM3 is short-circuited with the terminal TM3 of the switch S11. The output of the amplifier 20 is the switch S11.
Of the switch S11, and the terminal TM1 of the switch S11 is connected to the output terminal T2.

The operation of the variable gain circuit having such a configuration is as follows. For example, the received power of the received wave is
When the amplification is so large that it is not necessary, the switch control unit 23 controls the switches S10 and S11 so that the terminal TM1 is switched to the terminal TM3. As a result, the RF signal input from the input terminal T1 is transferred to the terminal TM1 → TM of the switch S10.
The signal is output from the output terminal T2 without being amplified through the terminal 3 → TM1 of the switch 3 → switch S11. On the other hand, when the received power of the received wave is small enough to require amplification, the switch controller 23 controls the terminals T of the switches S10 and S11.
Both of M1 are switched to the terminal TM2. In this case, the RF signal input from the input terminal T1 is amplified by the amplifier 20 and then supplied to the output terminal T2. In the variable gain circuit shown in FIG. 9, the switches S10 and S11 are switched according to the level of the received wave as described above, so that the signal path to which the gain is given via the amplifier 20 and the path through the amplifier 20 are passed. Then, a signal path that is output without being amplified is formed, and thus the gain of the RF signal is variable. In the case of such a configuration, 0 dB due to the signal path not passing through the amplifier 20
And a gain based on a predetermined amplification factor set for the amplifier 20 can be obtained as a variable gain circuit.

Here, the switches S10 and S shown in FIG.
A specific configuration example of 11 is shown in the circuit diagram of FIG. The switches S10 and S11 are, for example, four field effect transistors (hereinafter referred to as FETs) 101, 102, 103,
By connecting 104 as shown in the figure, a signal input to the terminal TM1 is selectively output to either of the terminals TM2 and TM3, so-called SPDT (Single Pole).
Double Throw) switch. In this case, for example, the FET 101 is turned on and the FET 102 is turned off, whereas the FET 103 is turned off and the FET 1 is turned on.
It is possible to obtain a state in which the terminal TM1 is switched with respect to the terminal TM2 by controlling 04 to be turned on. Then, the FET 101 is turned off and the FET 102 is turned on so that the on / off states of the respective FETs are reversed.
Are controlled to be turned on, the FET 103 is turned on, and the FET 104 are turned off, so that the terminal TM1 is turned on.
The state switched to M3 is obtained.

[0007]

By the way, in the case of the variable gain circuit having the above-mentioned configuration, the received RF signal always passes through the switches S10 and S11. These switches S10 and S11 are formed of FETs as described with reference to FIG. 10, but it is known that loss occurs when a signal passes through these FETs. Since the variable gain circuit as shown in FIG. 9 is provided for the reception front end section of a mobile communication terminal, for example, attenuation of signal strength due to power loss as described above adversely affects reception sensitivity. There is a problem of causing. Further, the switches S10 and S11 as shown in FIG. 9 are SPDT switches as described above, but in order to form this type of switch, for example, as shown in FIG. FETs are required, so the cost will be higher. Furthermore,
In a transmission / reception device or the like provided with such a variable gain circuit, it is preferable that the power consumption be as low as possible from the viewpoint of battery life and the like.

[0008]

In order to solve the above problems, the present invention solves the above-mentioned problems by amplifying means for amplifying an input signal, a first impedance inverting line for inverting the impedance characteristic of a transmission signal, and a second impedance. A transmission line formed by connecting inversion lines in series and provided so as to pass through the amplifying means, and a connection portion between the first impedance inversion line and the second impedance inversion line with respect to the ground, depending on switching on / off. Switch means provided so that connection / disconnection is set, and switch control means for controlling ON / OFF of the switch means based on intensity information of a signal to be input to the variable gain circuit, for example. The variable gain circuit is configured as a provision. At this time, switch means inserted into the power supply line to the amplifying means and turned on / off by the switch control means is provided.

Further, an amplifying means for amplifying the input signal, a first impedance inverting line and a second impedance inverting line for inverting the impedance characteristic with respect to the transmission signal are connected in series, and an end portion on the first impedance inverting line side is connected. Is connected to the input side of the amplifying means, and the end portion on the side of the second impedance inverting line is connected to the output line of the amplifying means and the power supply input line. And connecting / disconnecting the connection portion between the first impedance inverting line and the second impedance inverting line with respect to the ground, and the switch means provided so that supply / stop of power to the amplifying means is set. It was decided to construct a variable gain circuit.

Further, according to the above configuration, since the high frequency signal supplied to the variable gain circuit is output without passing through the switch circuit formed by the FET, the power of the signal due to passing through this switch circuit. The loss will be eliminated. Further, when the signal path passing through the amplifier is selected, the power supply to the amplifier is stopped.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a variable gain circuit of the present invention will be described below with reference to FIGS. FIG. 1 is a block diagram showing a configuration example of a transmission / reception apparatus as a mobile communication terminal including a variable gain circuit according to an embodiment of the present invention. First, in the configuration of the reception system of this transmission / reception device, the radio wave received by the antenna 1 is supplied to the reception amplifier 3 as an RF signal by the transmission / reception duplexer 2. In the reception amplifier 3, the gain is varied according to the power of the reception signal, and the high frequency signal output from the reception amplifier 3 is mixed with the local frequency from the local oscillator 5 by the mixer 4 to be an intermediate frequency signal. The gain of the intermediate frequency signal is variably controlled by the variable intermediate frequency gain amplifier 6, and the output is demodulated by the demodulator 7 to be converted into a baseband signal and supplied to the baseband signal processing circuit 8.

As a structure of the transmission system, the transmission baseband signal output from the baseband signal processing circuit 8 is modulated by the modulator 10 and amplified by the intermediate frequency variable gain amplifier 11 in a required gain state. Then, the mixer 12 mixes it with the local frequency from the local oscillator 5 to form a high frequency signal (radio frequency signal), which is amplified by the radio frequency gain variable amplifier 13. Further, the transmission power amplifier 14
Is amplified by, and is supplied from the transmission / reception duplexer 2 to the antenna 1 and is transmitted and output.

The controller 10 varies the gain set in the receiving amplifier 3 and the variable intermediate frequency gain amplifier 6 in the receiving system, for example, based on the information signal of the received signal strength supplied from the baseband signal processing circuit 8. Output a control signal for. Further, to the transmission system, a control signal is output based on an information signal having the same received signal strength as described above or an instruction signal from a partner station such as a base station, and the intermediate frequency gain variable amplifier 11 and the radio frequency gain variable amplifier Amplifier 1
3 and the gain in the transmission power amplifier 14 are variably set.

In the transmitter / receiver shown in this figure, the gain of the reception signal or the transmission signal is varied by both the RF signal stage and the IF signal stage in each of the reception system and the transmission system. Is due to the following reasons. Taking the reception system as an example, in a system in which the power fluctuation of the signal received by the antenna becomes extremely large,
Corresponding to this, it is necessary to give a wide variable gain width of the received signal, but due to limitations such as the dynamic range of the constituent elements and the isolation of the input / output system, one variable gain circuit can have a wide variable gain as described above. It is difficult to give a gain range, and it is not preferable from the viewpoint of reception sensitivity. Therefore, for example, in the case of a receiving system like the transmitting / receiving apparatus shown in FIG. 1, the receiving amplifier 3 (RF
Signal stage) and the intermediate frequency variable gain amplifier 6 (IF signal stage) to share the variable gain of the received signal,
It is designed to support a wide variable gain range. Specifically, for example, the required total variable gain width is 80d.
In the case of about B, the variable gain width of 30 dB is given to the receiving amplifier 3 and the variable gain width of 50 dB is given to the intermediate frequency variable gain amplifier 6.

In the transmitter / receiver configured as described above, the variable gain circuit of the present invention has the RF in the receiving system.
It is supposed to be applied to the reception amplifier 3 that amplifies the reception signal. Therefore, an example of the configuration of the variable gain circuit of this embodiment, which is the receiving amplifier 3, will be described below with reference to FIGS.

FIG. 2 is a block diagram showing a first example of the variable gain circuit according to the present embodiment. The same parts as those shown in FIG. 9 described above as a conventional example are designated by the same reference numerals and the description thereof will be omitted. In the variable gain circuit shown in this figure, first, the input terminal T1
Is connected to the input of the amplifier 20, and the output terminal T2 is connected to the output of the amplifier 20. In this case, the DC power output from the power supply unit 24 to the amplifier 20 is the switch S.
1 can be supplied. In this case, the switch S1 operates so that one contact is connected or disconnected to the other contact, that is, a so-called SPST (Sing).
le PoleSingle Throw) switch is used. Further, in the present embodiment, the quarter wavelength transmission line 21 and the quarter wavelength transmission line 22 are connected in series, and this series connection is provided in parallel with the amplifier 20 as shown in the figure. The connecting portion between the 1/4 wavelength transmission line 21 and the 1/4 wavelength transmission line 22 is grounded to the ground via the switch S2 of the SPST. The 1/4 wavelength transmission line 21 and the 1/4 wavelength transmission line 22 are each assumed to have a characteristic of passing a signal frequency of the 1/4 wavelength with respect to a wavelength corresponding to the transmission signal frequency. This has the effect of inverting the impedance characteristic with respect to the transmission signal frequency. The switch control unit 23 outputs a control signal for turning on / off the switches S1 and S2 based on the information signal output from the controller 10 shown in FIG.

In the variable gain circuit of the present embodiment configured as described above, for example, when the received signal has a signal strength that does not require amplification in the RF signal stage, the controller 10 to the switch control unit 23. In contrast, an information signal corresponding to the above signal strength state is supplied. In this case, the switch control unit 23 controls both the switches S1 and S2 to be turned off. According to this, first, the switch S1 is turned off to stop the power supply to the high frequency amplifier 20,
The operation of the amplifier 20 will also be stopped. Further, the switch S2 is turned off and the quarter-wave transmission lines 21 and 22 are
By disconnecting the connection point of from the ground, the impedance of the transmission line of the quarter wavelength transmission lines 21 and 22 connected in series can be ignored. Therefore, in this case, the RF reception signal input from the input terminal T1 is not amplified by the 1/4 wavelength transmission line 21 → 1/4 wavelength transmission line 22 without passing through the amplifier 20. In this state, it is output from the output terminal T2.

On the other hand, when the strength of the received RF signal is weakened to the extent that amplification is required and the controller 10 outputs the information signal corresponding to this signal state, The switch control unit 23 controls both the switches S1 and S2 to be turned on.
As a result, the switch S1 is turned on to form a line for supplying the DC power from the power supply unit 24 to the amplifier 20, and the amplifier 20 becomes operable. Then, the switch S2 is turned on, and the quarter wavelength transmission line 21,
Since the connection point of 22 is grounded, the impedance of the line of the quarter wavelength transmission line 21 viewed from the input terminal T1 is inverted and becomes infinite. Further, the impedance of the line of the quarter wavelength transmission line 22 viewed from the output terminal T2 becomes infinite in the same manner. Therefore, in this case, the signal path of the 1/4 wavelength transmission line 21 → 1/4 wavelength transmission line 22 connected in series is invalid for the input signal, and all the RF signals input from the input terminal T1 are amplified. And is amplified based on the gain set in the amplifier 20. Therefore, all the signals output from the amplifier 20 are also output from the output terminal T2.

The variable gain circuit of this embodiment is configured to vary the gain to be given to the input signal as described above. Then, for example, in the case of the variable gain circuit shown in FIG. 9 as a conventional example, the input signal is output after passing through the switch composed of the FET, whereas in the present embodiment, such a switch is It is designed so that it cannot be provided in the signal path. As a result, in the present embodiment, it is possible to eliminate the loss due to the signal input to the variable gain circuit passing through the switch. Further, in the variable gain circuit shown in FIG. 9, the switches S10 and S11 have four switches, respectively.
Although the SPDT switch formed by using the FET of the book was used, the switches S1 and S2 of SPST shown in this figure are used.
Can be formed by a smaller number of FETs, which is advantageous in terms of cost. Further, in the present embodiment, the power supply to the amplifier 20 is stopped by the switch S1 when the amplification is not performed, so that the power consumption can be reduced in the time average. become.

FIG. 3 is a block diagram showing a configuration of a variable gain circuit according to a second embodiment of the present invention, and the same portions as those in the previous embodiment shown in FIG. The description is omitted. In the variable gain circuit shown in this figure, 1 / with respect to the line between the input terminal T1 and the input of the amplifier 20.
The 4-wavelength transmission line 25 is inserted and the input of the amplifier 20 is connected to the ground via the switch S3 of SPST. Further, the output line of the amplifier 20 and the output terminal T2
A quarter wavelength transmission line 26 is inserted between the two, and a SPST switch S4 is inserted between the output of the amplifier 20 and the ground.

In this case, the switch control section 23 controls the on / off of the switches S1, S2, S3 and S4. When the input signal is not amplified (non-amplified), the switch S1,
Control is performed so that both S2 are turned off and both switches S3 and S4 are turned on. Also, when amplifying the input signal (during amplification)
In this case, the switches S1 and S2 are both turned on, and the switches S3 and S4 are both turned off.

In the variable gain circuit having such a configuration, when the input signal is not amplified, the switches S1, S2, S3, and S4 corresponding to the above-described non-amplification state are set to the switching state. As in the case of, the power supply to the amplifier 20 is stopped and the amplifier 20 is deactivated,
Since the connection part of the four-wavelength transmission lines 21 and 22 is separated from the ground, the input signal is 1 / 4-wavelength transmission lines 21 and 2.
It is output via two serially connected lines. In this embodiment, the switch S3 is turned on at this time and the end of the quarter-wave transmission line 25 is grounded, so that the quarter-wave transmission line 2 seen from the input terminal T1.
The impedance to the input of the amplifier 20 via 5 becomes infinite. Similarly, the switch S4 is turned on and the end of the quarter wavelength transmission line 26 is grounded, so that the impedance to the output to the amplifier 20 as viewed from the output terminal becomes infinite. That is, in this case 25, 26
Thus, the amplifier 20 is isolated from the input terminal T1 and the output terminal T2. As a result, when compared with the embodiment of FIG. 2, for example, it is possible to more reliably reduce the signal loss when passing through the amplifier 20 without amplifying the input signal.

On the other hand, in the case where the switches S1, S2, S3, S4 are in the switching state corresponding to the above-mentioned amplification for amplifying the input signal, the power is supplied to the amplifier 20. At the same time, the connection point of the quarter wavelength transmission lines 21 and 22 is grounded. At this time, the switches S3 and S4 are both turned off,
The RF signal input from the input terminal T1 is generated by disconnecting both ends of the four-wavelength transmission lines 25 and 26 from the ground.
The received signal is 1/4 wavelength transmission line 25 → amplifier 20 → 1
By passing through the / 4 wavelength transmission line 26, a gain is given and the signal is output from the output terminal T2, and the signal path is equivalent to the case of FIG.

FIG. 4 is a block diagram showing the configuration of a variable gain circuit as a third embodiment. The same parts as those in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted. In the variable gain circuit shown in this figure, a matching circuit 27 that performs impedance matching with respect to the input terminal T1 is provided, and its output is connected to the gate of the FET 20A which is the amplifier of the present embodiment via the DC blocking capacitor C1. Connected. Further, in this case, the gate of the amplifier 20A is connected to the gate bias voltage Vgg via the resistor R1. In addition, FET20
The drain of A has a DC blocking capacitor C2 and a matching circuit 2
8 is connected to the output terminal T2. FET2
The source of 0A is grounded.

In the case of the present embodiment, as a path for bypassing the FET 20A, a DC blocking capacitor C3 → 1/4 wavelength transmission line 21 → 1 / between the gate and drain of the FET 20A as shown in the figure. 4 wavelength transmission line 2
2 are provided so as to be connected in series. And
The connection point of the ¼ wavelength transmission lines 21 and 22 is connected to the power supply unit 24 via the switch S1 and branched and connected to the ground via the DC blocking capacitor C4. In this case, the switch control unit 23 controls the on / off operation of only the switch S1.

In the variable gain circuit of this embodiment,
For example, when the received signal needs to be amplified, the switch control unit 23 controls the switch S1 to be turned on based on the information signal from the controller 10. In this case, the DC power output from the power supply unit 24 is supplied from the switch S1 through the quarter wavelength transmission line 22 to the drain as the operating power of the FET 20A. Further, since the connection point of the 1/4 wavelength transmission lines 21 and 22 is connected to the ground via the DC blocking capacitor C4, the impedance of the line of the 1/4 wavelength transmission line 21 seen from the input terminal T1 side is infinite. Further, the impedance of the line of the quarter wavelength transmission line 22 as viewed from the output terminal T2 side becomes infinite. Therefore, the input signal is amplified by the FET 20A and output from the output terminal T2 via the DC blocking capacitor C2 and the matching circuit 28.

On the other hand, when it is not necessary to amplify the received signal, the switch controller 23 switches the switch S
1 is turned off, whereby the power supply from the power supply section 24 to the FET 20A is stopped, and the FE
T20A becomes inoperable. Further, since the connection point of the 1/4 wavelength transmission lines 21 and 22 is disconnected from the ground because the switch S1 is turned off, the input signal is transmitted from the DC blocking capacitor C3 to the 1/4 wavelength transmission line 21 → 1.
It is output via the path passing through the series connection of the / 4 wavelength transmission line 22, and the amplification by the FET 20A is not performed.

When the variable gain circuit is configured as in the present embodiment, the input signal is prevented from passing through the switch regardless of the presence or absence of the amplifying operation as in the previous embodiments. The switching of the power supply to the amplifier (FET 20A) and the switching of the passage of the input signal.
The switch S1 also has a dual function. This makes it possible to reduce the number of switches to be provided in the variable gain circuit in the present embodiment, which is more advantageous in terms of cost.

By the way, in each of the embodiments described so far, the connection form is based on the transmission lines of the quarter wavelength transmission lines 21 and 22 connected in series to the amplifier 20 or the amplifier such as the FET 20A. It can be considered that a return path is formed. Therefore, depending on the actual usage, when the amplification signal path and the non-amplification signal path are not reliably isolated from each other, especially when amplifying, the output of the amplifier is 1 /
It is conceivable that feedback may occur via the lines of the four-wavelength transmission lines 21 and 22 to cause oscillation in the loop. Further, for frequencies other than the reception frequency, the quarter-wave transmission line of the present embodiment does not actually have a quarter-wavelength, so there is a possibility of oscillation due to components other than the reception frequency. Therefore, hereinafter, a configuration of a variable gain circuit to which a configuration for preventing oscillation as described above is added will be described as an embodiment of the present invention.

FIG. 5 shows a fourth embodiment having the above-mentioned oscillation preventing structure.
2 is a block diagram showing a configuration of a variable gain circuit as an embodiment of FIG. The basic configuration of the variable gain circuit shown in this figure is the same as that of the variable gain circuit according to the embodiment shown in FIG. 1. Therefore, the same parts as those in FIG. In this case, a so-called tank resonance circuit is formed by a parallel resonance circuit in which the capacitor Cr and the inductor Lr are connected in parallel, and the resonance frequency thereof is set so that the impedance becomes infinite with respect to the reception frequency. This parallel resonant circuit is provided such that one end of its parallel connection is connected to the connecting portion of the quarter-wave transmission lines 21 and 22 and the other end is grounded as shown in the figure. With such a configuration, components other than the reception frequency, which are about to pass through the transmission line composed of the quarter-wave transmission lines 21 and 22, are made to fall to the ground through the parallel resonant circuit. It is possible to prevent oscillation due to signal components other than the reception frequency.

Further, in the variable gain circuit shown in FIG. 6 as the fifth embodiment, a series resonance circuit is formed by a capacitor Cr and an inductor Lr which are selected so that impedance becomes large for signal components other than the reception frequency. It is formed and inserted between the connecting portions of the quarter-wave transmission lines 21 and 22 as shown in the figure. However, even with this configuration, except the reception frequency, the same operation as the variable gain circuit of FIG. 5 is performed. It is possible to prevent oscillation due to the signal component of. In this figure, the same parts as those in FIG.

FIG. 7 is a block diagram showing the configuration of a variable gain circuit as a sixth embodiment. The same parts as those in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted. In the variable gain circuit shown in this figure, an isolator IS is inserted between the connection parts of the signal lines of the quarter-wave transmission lines 21 and 22 connected in series. In this case, the isolator IS is used.
As indicated by the arrow in the figure, it is provided in the transmission direction in which signals are transmitted from the 1/4 wavelength transmission line 21 side to the 1/4 wavelength transmission line 22 side. Further, in this case, instead of the switch S2, the switches S5 and S6 of SPST are provided between both ends of the isolator IS and the ground, respectively.
Is provided.

In the variable gain circuit having this structure, when the input signal is amplified, the switch control section 23 controls the switches S1, S5 and S6 so that they are all turned on. As a result, the amplifier 20 is supplied with power and is in an operable state. Further, since the switch S5 is turned on and the end of the 1/4 wavelength transmission line 21 is grounded, the impedance of the 1/4 wavelength transmission line 21 as seen from the input terminal T1 becomes infinite, and similarly the switch S6 is used. As a result, the end of the quarter-wave transmission line 22 is grounded, so that the impedance of the quarter-wave transmission line 22 viewed from the output terminal T2 becomes infinite. As a result, the input signal is supplied to the amplifier 20 and after being amplified,
It is output from the output terminal T2. At this time, the signal component that is output from the amplifier 20 and is about to be fed back to the input side of the amplifier via the quarter wavelength transmission line 21 is the isolator IS.
Therefore, the oscillation in the loop is prevented from occurring.

When it is not necessary to amplify the input signal, the switch control unit 23 causes the switch S1,
It is controlled so that S5 and S6 are all off. In this case, the amplifier 20 is not supplied with power and its operation is stopped, and each end of the quarter wavelength transmission lines 21 and 22 is separated from the ground, so that the input signal is transmitted through the quarter wavelength. Line 21 → isolator IS → quarter wavelength transmission line 22
And is supplied to the output terminal T2 without being amplified.
Further, in this case, since the signal passing through the isolator IS is considered to have no loss, power loss with respect to the passing signal does not occur.

FIG. 8 is a block diagram showing the configuration of the variable gain circuit as the seventh embodiment. The same parts as those in FIG. 7 are designated by the same reference numerals and the description thereof will be omitted. The variable gain circuit shown in this figure has a configuration in which the isolator IS previously provided in the embodiment shown in FIG. 7 is replaced by a switch S7. Then, when the signal is amplified in the variable gain circuit of this embodiment, the switches S1, S5, S6 are turned on and the switch S7 is turned off by the switch control unit 23. As a result, the circuit becomes equivalent to the case described in FIG. 7, the input signal is amplified by the amplifier 20, and
It is output without any signal loss. Further, in this case, since the switch S7 is in the off state,
Since the connecting portions of the quarter-wave transmission lines 21 and 22 are in a circuit-isolated state, in-loop oscillation is prevented as in the case of FIG. 7. When the input signal is not amplified, the switch control unit 23 controls the switches S1, S5, S6 to be off and the switch S7 to be on. Thereby, the input signal is 1/4 wavelength transmission line 21 → switch S7 → 1/4
The signal is output from the output terminal T2 without being amplified via the wavelength transmission line 22. In the case of the present embodiment, during this non-amplification, the signal passes through the switch S1 of SPST. For example, as shown in FIG. 9 as a conventional example, the signal passes through the switches S10 and S11 of SPDT. The degree of signal loss is improved when compared with the.

It should be noted that, as each of the above-described embodiments, FIGS.
The variable gain circuit shown in FIG. 1 has been described as being applied to the reception amplifier 3 in the transmission / reception apparatus shown in FIG. 1 as described above, but is a circuit block for changing the gain of another reception signal or transmission signal. The present invention can also be applied to the intermediate frequency variable gain amplifiers 6 and 11, the radio frequency variable gain amplifier 13, and the transmission power amplifier 14. Also,
Each of the embodiments having the configuration for suppressing the in-loop oscillation shown in FIGS. 5 to 8 can be applied to the variable gain circuit having the configuration as shown in FIGS. 3 and 4, though not shown. It Further, the detailed configuration of the variable gain circuit and the configuration of the transmitter / receiver including the variable gain circuit of the present invention are not limited to the configurations described so far, and can be changed according to actual use conditions and the like. It is said that

[0037]

As described above, in the variable gain circuit of the present invention, two impedance inversion lines connected in series to the amplifier are provided in parallel, and the connection point of the impedance inversion lines connected in series and the ground. On /
SPST whose conduction / non-conduction is switched by the off operation
A switch is provided, and by switching the switch on / off, switching between a signal path in which an input signal is amplified by an amplifier and a signal path in which the input signal passes through the series-connected impedance inverting line and is not amplified is output. With this configuration, the input signal can be output without passing through the switch circuit formed by the FET, for example. As a result, the signal input to the variable gain circuit of the present invention is output without being affected by the loss of the switch circuit. For example, the dynamic range of the variable gain circuit itself is expanded in consideration of the loss of the signal. It is possible to realize the improvement of the reception sensitivity without performing the above. Further, in the present invention, since the switch by SPST is used for the switching control of the signal path at the time of amplification and at the time of non-amplification, as compared with the case where the switch circuit of SPDT is conventionally used, the switch It is possible to reduce the number of FETs required for formation and reduce the cost. Further, in the present invention, when the signal path for non-amplification is selected, the power supply to the amplifier is configured to be stopped, whereby, for example, a transmitter / receiver device including the variable gain circuit of the present invention is used. It is also possible to reduce power consumption.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration example of a transmission / reception device including a variable gain circuit according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a variable gain circuit according to the present embodiment.

FIG. 3 is a block diagram showing a configuration of a variable gain circuit according to the present embodiment.

FIG. 4 is a block diagram showing a configuration of a variable gain circuit according to the present embodiment.

FIG. 5 is a block diagram showing a configuration of a variable gain circuit according to the present embodiment.

FIG. 6 is a block diagram showing a configuration of a variable gain circuit according to the present embodiment.

FIG. 7 is a block diagram showing a configuration of a variable gain circuit according to the present embodiment.

FIG. 8 is a block diagram showing a configuration of a variable gain circuit according to the present embodiment.

FIG. 9 is a block diagram showing a configuration example of a variable gain circuit as a conventional example.

FIG. 10 is a circuit diagram showing a configuration example of a switch used in a conventional variable gain circuit.

[Explanation of symbols]

 3 reception amplifier 6, 11 intermediate frequency variable gain amplifier 9 controller 13 radio frequency variable gain amplifier 14 transmission power amplifier 20 amplifier 20A FET (variable gain circuit) 21, 22, 25, 26 1/4 wavelength transmission line 23 switch control section 24 Power supply unit T1 input terminal T2 output terminal S1 to S7 switch (SPST)

Claims (9)

[Claims] 1. An amplification means for amplifying an input signal, and a first means for inverting an impedance characteristic with respect to a transmission signal.
Of the impedance inversion line and the second impedance inversion line connected in series, the transmission line being provided so as to pass through the amplifying means, and the first impedance inversion line and the first impedance inversion line according to the switching of ON / OFF. Switch means provided so that connection / disconnection of the connection portion with the impedance inverting line 2 with respect to the ground is set, and by varying the gain with respect to the input signal by performing on / off control of the switch means. A variable gain circuit, comprising: a switch control means capable of performing the above. 2. The switching device according to claim 1, further comprising a switching device that is inserted into a power supply line to the amplifying device and is turned on / off by the switch control device. Variable gain circuit. 3. A third impedance inverting line that is inserted into the signal input line of the amplifying means to invert the impedance of the transmission signal, and is inserted between the output end of the third impedance inverting line and ground. ON / OFF by the switch control means
A switch means whose OFF is controlled, a fourth impedance inversion line which is inserted in the signal output line of the amplification means and inverts the impedance of the transmission signal, and between the input end of the fourth impedance inversion line and the ground. Is turned on / off by the switch control means.
2. The variable gain circuit according to claim 1, further comprising switch means whose off is controlled. 4. A signal frequency selecting means is provided for the transmission line, and is provided with a signal frequency selecting means for passing only the frequency component of the signal to be supplied to the variable gain circuit through the transmission line. The variable gain circuit according to claim 1. 5. The variable gain according to claim 1, further comprising an isolator inserted in a connection portion between the first impedance inverting line and the second impedance inverting line in the transmission line. circuit. 6. An amplifying means for amplifying an input signal, a first impedance inversion line for inverting the impedance of a transmission signal and a second impedance inversion line are connected in series, and an end portion on the side of the first impedance inversion line. Is connected to the input side of the amplifying means, and the end portion on the side of the second impedance inversion line is connected to the output line of the amplifying means and the power supply input line, and according to the switching of ON / OFF. And a switch means provided so that connection / non-connection of the connection portion between the first impedance inverting line and the second impedance inverting line to the ground and supply / stop of power supply to the amplifying means are set. A switch control unit capable of varying a gain with respect to an input signal by performing on / off control of the switch unit; A variable gain circuit, comprising: 7. A third impedance inversion line, which is inserted into a signal input line of the amplification means and inverts impedance characteristics with respect to a transmission signal, and is inserted between an output end of the third impedance inversion line and ground. ON by the switch control means
A switch means whose OFF is controlled, a fourth impedance inversion line which is inserted in a signal output line of the amplification means and which inverts impedance characteristics with respect to a transmission signal, and between an input end of the fourth impedance inversion line and ground. Is turned on / off by the switch control means.
7. The variable gain circuit according to claim 6, wherein the variable gain circuit comprises: switch means whose OFF is controlled. 8. A signal frequency selecting means is provided which is provided for the transmission line and which allows only a frequency component of a signal to be supplied to the variable gain circuit to pass through the transmission line. The variable gain circuit according to claim 6. 9. The variable gain according to claim 6, further comprising an isolator inserted in a connection portion between the first impedance inverting line and the second impedance inverting line in the transmission line. circuit.