JPH01248706A - High frequency amplifier with switch - Google Patents

Abstract

PURPOSE:To interrupt an input signal given to a base at bias voltage OFF and to reduce the leakage signal level with simple circuit constitution by applying the input signal and a base bias voltage to a base of a transistor(TR) via a diode. CONSTITUTION:With a transmission output off-state commanded, a base bias voltage VBB is interrupted into 0V, and a voltage applied across an input diode 21 is lowered and it is turned off and the input resistance reaches several hundreds kOMEGA. Since a base-emitter voltage of a transistor(TR) 13 is nearly 0V, the TR 13 stops its amplifying function. The signal level of an input signal (d) given from an input terminal 11 is attenuated considerably by the input diode 21 and the resulting signal is fed to the base of the TR 13. Since the amplification function of the TR 13 is stopped, however, the signal level of an output signal (c) is very small. Thus, the input signal given to the base is cut off and the leakage signal level of the output signal is reduced with simple circuit constitution.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a high frequency amplifier using transistors,
In particular, by changing the base bias voltage, you can turn on the output signal.
This invention relates to a high frequency amplifier with a switch for off control.

[Prior Art] For example, some high-frequency amplifiers incorporated in transmitters that use high-frequency waves with a carrier frequency of about several 100 MHz have a switch mechanism. A transmitter incorporating a high frequency amplifier with a switch having such a switch function is configured as shown in FIG. 2, for example. That is, a high frequency signal a output from a high frequency signal source 1 is amplified by a high frequency amplifier with a switch 2, power amplified by a power amplifier 3, and radiated into the air via an antenna 4. The high frequency amplifier with switch 2 controls on/off the output signal C to be sent to the power amplifier 3 in accordance with the transmission control signal inputted from the transmission control section 5.

This high frequency amplifier 2 with a switch has a circuit configuration shown in FIG. 3, for example. A high frequency input signal d (high frequency signal a) sent from the high frequency signal source 1 is input to the base of an npn type transistor 13 via an input terminal 11 and a coupling capacitor 12. A DC base bias voltage V is applied to the base of this transistor 13 via a resistor 14.
BB is applied. And this base bias voltage V
BB is variably controlled by a transmission control signal sent from the transmission control section 5.

In addition, a base resistor 15 is connected between the base and ground,
A parallel circuit including a resistor 16 and a capacitor 17 is inserted between the emitter of the transistor 13 and ground. The output taken out from the collector is a pair of capacitors 18a and 18b.
The output signal C is sent to the power amplifier 3 as an output signal C via a tuning circuit 18 consisting of a variable coil 18c and an output terminal 19.

Further, the collector of the transistor 13 is connected to the DC collector 7 [EV] via the above-mentioned flexible coil 18c. .

is applied. Note that a capacitor 20 is inserted between the variable coil 18C and ground.

In such a high-frequency amplifier 2 with a switch, when a high-frequency signal a is applied to the base of the transistor 13 via the input terminal 11 with the base bias voltage VBB and collector voltage VCC controlled to constant voltages optimal for this amplifier, This input signal a is amplified by the transistor 13 and output as an output signal C from the collector to the output terminal 19 via the tuning circuit 18. Note that the output signal C has an unnecessary frequency component ρ (removed by the tuning circuit 18).

When the output signal C output from the output terminal 19 is cut off (turned off), the base bias voltage VBB applied to the base of the transistor 13 is cut off using the transmission control signal from the transmission control section 5. Collector current stops flowing and output signal C is cut off.

That is, by variably controlling the base bias voltage V[lB with the transmission control signal, the output signal C can be controlled on/off without controlling the input signal d on/off.

[Problems to be Solved by the Invention] However, the high frequency amplifier with switch shown in FIG. 3 still has the following problems to be solved. In other words, in general, the amplification characteristics of a transistor are as follows:
Since the collector voltage VCC is applied to the collector,
Even if the base bias voltage VBII is lowered to Ov, a small collector current flows. therefore,
As long as the input signal d is applied, a minute output signal C corresponding to the input signal d is output from the output terminal 19.

Then, the signal level of the output signal C input to the power amplifier 3 when the transmission control signal SGA from the transmission control unit 5 instructs the transmission output OFF state and the base bias voltage VBB is Ov is the signal level of the transmission control signal SGA that is input to the power amplifier 3. Since the signal level of the output signal C is not sufficiently attenuated when the output signal is turned on and the base bias voltage VI is constant, even when the transmission output is off, the intensity from the antenna 4 is greater than the allowable value. There is a problem that radio waves with .

In order to eliminate this inconvenience, the high frequency amplifier 2 with a switch shown in FIG. 3 is interposed in multiple stages between the high frequency signal source 1 and the power amplifier 3 shown in FIG. It is considered to increase the signal level difference between the on-time and off-time of the output signal C of the high-frequency amplifier with switch 2 at the final stage by sequentially reducing the leakage signal level of the output signal C of each stage. .

However, if a plurality of switch-equipped high-frequency amplifiers 2 as shown in FIG. 3 are provided, not only the circuit configuration of the entire transmitter becomes complicated, but also the entire device becomes larger and the manufacturing cost increases.

By applying an input signal and a base bias voltage to the base of a transistor through a diode, the present invention can block the input signal input to the base when the bias voltage is off, and with a simple circuit configuration, when the transmission output is off, An object of the present invention is to provide a high-frequency amplifier with a switch that can significantly reduce the leakage signal level of an output signal in a high-frequency amplifier.

Another object of the present invention is to provide a high-frequency amplifier with a switch that can further reduce the leakage signal level of the output signal by inserting a diode on the collector side in addition to the base side.

[Means for Solving the Problems] The present invention applies an input signal to the base of a transistor, extracts an amplified output signal from the collector of this transistor, and changes the base bias voltage applied to the base to output the signal. In a high frequency amplifier with a switch that controls signals on and off, an input signal and a base bias voltage are applied to the base via a common input diode.

In another invention, in addition to the input diode described above, an output signal is taken out from the collector via an output diode.

[Function] If the high frequency amplifier with switch is configured in this way,
The input signal and base bias voltage are applied to the base of the transistor through the input diode. When the transmission output is on and the base bias voltage is normally applied, the input diode is in the on state because the base bias voltage is applied in the forward direction, and the input signal is applied to the base as it is, so normally output signal level is obtained.

On the other hand, when the transmission output is off, in which the base bias voltage is cut off, the base bias voltage is not applied to the input diode in the forward direction, so the input diode is in the off state. Therefore, when the signal level of the input signal is less than the forward voltage drop of the input diode, almost no current flows through this input diode, so the signal level of the output signal taken out from the collector of the transistor is greatly suppressed. Ru.

In addition to the above-mentioned effects, another invention has an output diode inserted on the collector side of the transistor, so when the transmission output is off, the base bias voltage is OV, so almost no collector current flows. , since the output diode is in the off state, the leakage signal level of the output signal is further reduced.

Note that when the transmission output is on and the base bias voltage is normally applied, a normal output signal level is obtained from the collector of the transistor as described above. Since a large collector current flows, the output diode is turned on, and the output signal passes through the output diode and is output.

[Example code] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing a high frequency amplifier with a switch according to an embodiment. The same parts as in the conventional switch-equipped high-frequency amplifier shown in FIG. 3 are given the same reference numerals.

An input terminal 11 to which an input signal d is input is connected to an np terminal via a coupling capacitor 12 and an input diode 21 with the polarity shown.
n-type transistor] 3. Further, a DC base bias voltage VB is applied to the base of the transistor 13 via the resistor 14 and the input diode 21 in the forward direction. This base bias pressure VBB is variably controlled by a transmission control signal sent from the transmission control section 5 shown in FIG. That is, when the transmission control signal is on, the base bias voltage VRB becomes a constant positive voltage, and when the transmission output is off, the base bias voltage VRB is cut off and becomes OV.

Further, the output signal C taken out from the collector of the transistor] 3 is outputted to one output terminal via the output diode 22 of the illustrated polarity and the tuning circuit 18. And the second
The signal is sent to the power amplifier 3 shown in the figure.

Further, a DC collector voltage V (C) is applied to the collector through the variable coil 18c and the output diode 22 in the forward direction.

In such a high frequency amplifier with a switch, when a transmission output ON state is instructed by a transmission control signal, a base bias voltage VaO is applied to the base while being controlled to a constant voltage that is optimal for this amplifier. Then, a collector current IC flows in the direction shown in the figure via the output diode 22.

In other words, this transistor 13 has a sufficient amplification function. In this state, the input signal d is sent to the input terminal 11.
When VBB is applied, at this point, the input diode 21 is in an on state because the base bias voltage VBB is applied in the forward direction.

Note that the internal resistance in this on state is, for example, several lOΩ.
It is. Therefore, a high frequency input signal d is applied to the base of the transistor 13 via this input diode 21. This input signal d is then amplified by the transistor 13, and an output signal C is taken out from the collector. In this state, the output diode 22 is in the on state due to the collector voltage aIc, so the resistance is several lOΩ, and the output signal C is connected to the output diode 22 and the tuning circuit 18.
The signal is outputted to the output terminal 19 through almost no attenuation.

Next, when the transmission output OFF state is instructed by the transmission control signal S, the base bias voltage Vaa is cut off and becomes OV. Then, the voltage applied across the input diode 21 decreases, turning the input diode 21 off, and the resistance becomes several hundred ohms. Furthermore, since the base-emitter voltage of transistor 13 becomes approximately OV, this transistor 13 stops its amplification function, and the collector current IC
almost no longer flows. Therefore 1. The output diode 22 is also turned off, and the resistance becomes several hundred ohms.

In this state, the input signal d input from the input terminal 11 has its signal level significantly attenuated by the input diode 21 and is applied to the base of the transistor 13. However, since this transistor 13 has stopped its amplification function, the signal level of the output signal C taken out from the collector becomes extremely low. Furthermore, the signal level of this output signal C is further attenuated by the output diode 22. Therefore, the signal level of the output signal C output from the output terminal 19 and sent to the power amplifier 3 in FIG. 2 when the transmission output is off is attenuated in two stages by the input diode 21 and the output diode 22.

In this way, by inserting the input diode 21 and the output diode 22 into the base circuit and collector circuit of the amplification transistor 13, the leakage signal level of the output signal C when the transmission output is turned off can be adjusted to the conventional circuit shown in FIG. This can be significantly reduced compared to the leakage signal level of the output signal C in . Therefore, it is possible to suppress the intensity of leakage radio waves radiated from the antenna 4 when the transmission output is off to below a permissible value without connecting high frequency amplifiers with switches in multiple stages.

Furthermore, since each of the diodes 21 and 23 is a small and inexpensive electronic component, the entire device can be made smaller and the manufacturing cost can be reduced compared to the case where the amplifier is configured in multiple stages.

In the embodiment shown in FIG. 1, the input diode 2
1 and an output diode 22 are provided, but the output diode 22 is removed and the input diode 2
Even if the configuration includes only 1, the signal level of the output signal C taken out from the collector becomes sufficiently low, so that the object of the present invention can be fully achieved.

[Effects of the Invention] As described above, according to the high frequency amplifier with switch of the present invention, the input signal and base bias voltage are applied to the base of the transistor via the diode. Therefore, the input signal input to the base can be blocked when the bias voltage is off, and the leakage signal level of the output signal when the transmission output is off can be significantly reduced with a simple circuit configuration. Furthermore, manufacturing costs can be significantly reduced compared to conventional circuits with the same performance.

Further, since a diode is inserted on the collector side in addition to the base side, the leakage signal level of the output signal can be further reduced, and the above-mentioned effects can be further improved.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing a high-frequency amplifier with a switch according to an embodiment of the present invention, Fig. 2 is a block diagram showing a transmitter using a high-frequency amplifier with a switch, and Fig. 3 is a conventional high-frequency amplifier with a switch. FIG. 2 is a circuit diagram showing a high frequency amplifier. 11...Input terminal, 13...Transistor, 18.
... Tuned circuit, one ... Output terminal, 21 ... Input diode, 22 ... Output diode, C ... Output signal, d ... Input signal, VBB ... Base bias voltage, VCC. ...Collector voltage. Applicant's agent Patent attorney Takehiko Suzue vss VCC Figure 1 Figure 2

Claims (2)

[Claims] (1) Apply the input signal (d) to the base of the transistor (13), take out the amplified output signal (c) from the collector of this transistor, and change the base bias voltage (V_B_B) applied to the base. The high frequency amplifier with a switch controls the output signal on and off by applying the input signal and the base bias voltage to the base via a common input diode (21). amplifier. (2) Apply the input signal (d) to the base of the transistor (13), take out the amplified output signal (c) from the collector of this transistor, and change the base bias voltage (V_B_B) applied to the base. In the high frequency amplifier with a switch, the input signal and the base bias voltage are applied to the base via a common input diode (21), and the output diode (21) is applied from the collector to the output diode (21). 22)
A high frequency amplifier with a switch, characterized in that the output signal is extracted through a switch.