JP2600640B2 - High frequency amplifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high frequency amplifier.

[0002]

2. Description of the Related Art A high frequency amplifier for amplifying an output signal is used in a radio communication device or the like, and this high frequency amplifier is generally constituted by an FET (field effect transistor). This FET generates heat in the operating state, and the amount of generated heat P _diss is expressed by _Equation 1.

[0003]

P _diss = V _d × I _d −P _OUT + P _{IN In} equation 1, V _d is the drain voltage of the FET, and I _d is F
The drain current of ET, P _IN is the power of the RF (radio frequency) signal input to the high frequency amplifier, and P _OUT is the power of the RF signal output from the high frequency amplifier.

As can be seen from equation (1), in the high-frequency amplifier, when the supplied power (drain voltage V _d × drain current I _d ) is constant, when the power P _{IN of the} input signal decreases, the output signal Since the power P _OUT is further reduced and the difference between the input and output powers (−P _OUT + P _IN ) is increased, the amount of generated heat P _diss is increased, and there is a problem that the channel temperature is increased. _diss
Is the largest. As described above, when the generated heat amount P _diss increases and the channel temperature increases, the reliability of the element is impaired and causes a failure.

As a countermeasure, it is conceivable to provide a cooling means for cooling the high-frequency amplifier. For example, in the case of a high-frequency amplifier used in a portable radio telephone, it is desired to reduce the size and power consumption of the telephone. It is desirable to avoid increasing the size of the telephone and increasing power consumption due to the provision of the cooling means. Similarly, in the case of a high-frequency amplifier used in a communication device of an artificial satellite, it is necessary to reduce the size of the communication device and reduce power consumption in order to operate the entire artificial satellite with low power. Not desirable.

As another measure, for example, Japanese Patent Publication No. 3-1
1683 JP, Sho 62-248301 discloses, as disclosed in JP-A-3-167909, the drain voltage V _d to 0 if there is no input signal, to FET for amplifying the signals by not supplying power Te, configure the high frequency amplifier capable of reducing power consumption (that is, the drain voltage V _d × drain current I _d) and the heat generation amount P _diss, JP 2-149
As disclosed in 108 JP, to reduce or zero drain current I _d and the gate voltage V _g below pinch-off voltage when there is no input signal, amplifies the signal F
By reducing power supply power (drain voltage V _d × drain current I _d in Equation 1) supplied to the ET, it is possible to configure a high-frequency amplifier capable of reducing power consumption and generated heat P _diss. Already known.

[0007]

However, the high-frequency amplifiers disclosed in each of the above-mentioned publications have a problem in that there is no input signal.
Since the drain voltage V _{d is set} to 0 or the drain current I _d is reduced or set to 0, the power P of the input signal is reduced.
_{When IN} is small, the rise in channel temperature due to the generated heat P _diss cannot be prevented.

Since the high-frequency amplifier may be used in the high-output region or in the low-output region, the conventional high-frequency amplifier in which the above-described measures are taken is also used in the low-output region, that is, the power P _{IN of the} input signal. In a region where is small, the amount of generated heat P _diss becomes a problem.

Therefore, even in the case where the power P _{IN of the} input signal is small, it is possible to apply a conventional technique to perform control for changing the bias in an analog manner so as to reduce the drain current I _d. It is conceivable, however, that the input signal power P
The gain (P _OUT / P _IN ) when _IN is small is greatly reduced. This will be described below with reference to FIG.

[0010] Figure 5 shows the input-output characteristics of the high-frequency amplifier when the power P _IN of the input signal is reduced drain current I _d as decreases.

In FIG. 5, the horizontal axis represents the power P _{IN of the} input signal.
And the vertical axis is the power P _OUT of the output signal. And
Indicates the output characteristic when the fixed bias by the dashed line shows the input-output characteristic when the power P _IN of the input signal is reduced drain current I _d as reduced by the solid line.

As can be seen from FIG. 5, when the input signal power P _IN is small, the solid line input / output characteristics deviate considerably from the broken line input / output characteristics, and the gain of the high-frequency amplifier is reduced. Therefore, there is a problem that the high-frequency amplifier cannot be used over a wide dynamic range.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described circumstances, and suppresses a rise in channel temperature by reducing the amount of heat generated when the power of an input signal to a high-frequency amplifier constituted by FETs is small, and at the same time, suppresses an increase in the input signal. It is an object of the present invention to provide a high-frequency amplifier that can obtain almost the same gain as that of a fixed bias even when the power is small.

[0014]

In order to achieve the above object, the present invention provides a power detecting means for detecting the power level of an input signal, an FET for amplifying the input signal, and a power level for the input signal. When the voltage is equal to or higher than the first predetermined value, the drain voltage and the gate voltage are set to specified values. When the power level of the input signal is lower than the first predetermined value and equal to or higher than the second predetermined value, the drain voltage is changed from the specified value. When the power level of the input signal is lower than the second predetermined value, the drain voltage is lowered to the lower limit of the predetermined range and the gate voltage is gradually lowered. And a power supply control circuit for performing control to lower the power consumption.

[0015]

According to the present invention, the power supply control circuit independently changes the drain voltage and the gate voltage, which are the bias voltages of the FET, based on the power level of the input signal detected by the power detection means. The amount of heat generated in the amplifier is not increased.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of a high-frequency amplifier according to the present invention.

The RF signal input from the input terminal 1 is input to the gate of the FET 4 for amplifying the RF signal. A part of the RF signal is detected by the directional coupler 2 and input to the power control circuit 3. Power supply control circuit 3 changes the gate voltage V _g and the drain voltage V _d of the FET4 in accordance with the level of the power P _IN of the input RF signal.

The drain current I _d of the FET4 is controlled by adjusting the gate voltage V _g, for example, -0.7 V gate voltage V _g from -0.5 V, is varied to -1.0 V, the drain current I _d from 80 to 900mA
It changes to 0 mA and 700 mA.

[0020] FET4 amplifies the RF signal from the input terminal 1 in response to the gate voltage applied from the power supply control circuit 3 V _g and the drain voltage V _d, and outputs to the output terminal 5.

[0021] FIG. 2 is in accordance with the drain voltage V _d FET4
FIG. 5 is a diagram showing the change in input / output characteristics of an RF signal, wherein the horizontal axis represents the power P _IN of the input RF signal, and the vertical axis represents the output amplified RF signal.
Signal power P _OUT .

[0022] In the figure, curves A, B, C is the input-output characteristics in the case where the drain voltage V _d 8V, 7V, the 6V respectively, in curves, the gate voltage V _g and the drain current I _d is constant is there.

On the other hand, FIG. 3 is corresponding to the drain current I _d F
It is a figure which shows the change of the input / output characteristic of ET4, the horizontal axis is the power P _IN of the input RF signal, and the vertical axis is the power P _OUT of the output amplified RF signal.

[0024] In the figure, curves D, E, F is the drain current I _d by varying the gate voltage V _g, respectively 9
00MA, 800 mA, an input-output characteristics when the 700 mA, in curves, the drain voltage V _d is constant.

Here, in the input / output characteristics of the FET 4, even if the power P _IN of the input signal changes, the power P of the output signal changes.
A region where _OUT shows almost the same value is called a saturation region, and a region where the power P _{OUT of the} output signal changes almost linearly in accordance with the change of the power P _IN of the input signal is called a small signal region.

As can be seen from FIG. 2, the drain voltage V _d
Is changed within a predetermined range, the saturation output changes in the saturation region depending on the drain voltage _Vd , but the input / output characteristics hardly change in the small signal region.
However, if the drain voltage _Vd is reduced beyond a predetermined range, the gain of the FET 4 will be significantly reduced regardless of whether it is in the saturation region or the small signal region.

As shown in FIG. 3, the gate voltage V _g
In the case where the drain current _Id is changed by changing the drain current Id, the saturation output in the saturation region does not depend on the drain current _Id and does not change much, but the gain of the FET 4 decreases in the small signal region.

FIG. 4 shows the bias voltage and the input / output characteristics in one embodiment of the high-frequency amplifier according to the present invention shown in FIG. 1, and (a) shows the power P _IN of the input RF signal and the power supply control circuit 3. bias voltage which is controlled by, that shows the relationship between the drain voltage V _d and the gate voltage V _g, (b) is an input-output characteristic of FET4 for amplifying the RF signal.

In FIG. 4A, a curve G is a curve showing the relationship between the gate voltage V _g and the input RF signal power P _IN, and a curve H is a drain voltage V _d and the input RF signal power P _{IN. This} is a curve showing the relationship with _IN , the horizontal axis is the power P _IN of the input RF signal, the right vertical axis is the voltage related to the curve G, and the left vertical axis is the voltage related to the curve H.

In FIG. 4B, the horizontal axis represents the power P _IN of the input RF signal, and the vertical axis represents the output RF signal.
Signal power P _OUT . The input / output characteristics in the case of the fixed bias are indicated by broken lines, and the input / output characteristics in the case where the bias voltage is changed as shown in FIG.

Since the amount of generated heat P _diss becomes a problem in the high-frequency amplifier in the small signal region, in this embodiment, when the high-frequency amplifier is used in the saturation region,
As shown in FIG. 4A, the drain voltage _Vd and the gate voltage _Vg are set to predetermined constant values (specified values) by the power supply control circuit 3 (in FIG. 4A, the drain voltage V
8V the _d, has a gate voltage V _g to -0.5V. ).

[0032] Then, when the power P _IN of the input RF signal is reduced to a small signal region from the saturation region, as shown in FIG. 4 (a), first, starts lowering the drain voltage V _d. In the small signal region, because although the power P _OUT of the input signal of the power P _IN output signal at a rate greater than the rate of decrease shown in Equation 1 is lowered, which lowers the drain voltage V _d, generated An increase in the amount of heat P _diss can be prevented. In this case, reduction in the drain voltage V _d is required to be suppressed to within a predetermined range mentioned above. This is because if the drain voltage _Vd is reduced beyond the predetermined range, the gain of the FET 4 is significantly reduced even in the small signal region as described above. Thus, by lowering the drain voltage V _d in a predetermined range in the small signal region, it is possible to prevent an increase in heat generation amount P _diss while obtaining substantially the same gain as when fixed bias.

[0033] After lowering the drain voltage V _d to the lower limit of the predetermined range, when using a high-frequency amplifier in the even smaller area power P _IN of the input signal, turn to deepen the gate voltage V _g (decrease let) reduces the drain current I _d by and prevent an increase in heat generation amount P _diss. According to the present invention, since the reduction in the drain current I _d only reduction in the drain voltage V _d is the heat generation amount P _diss increase prevention may be performed by an amount not sufficient, the drain current I
_Although the gain of the FET 4 is slightly reduced by decreasing _d , the decrease in gain can be reduced as compared with the case where only the drain current I _d is decreased, and the generated heat P _diss can be prevented from increasing.

By doing so, the input / output characteristics of the high-frequency amplifier according to the present invention have almost the same linearity as that at the time of fixed bias, and the heat quantity P _diss generated by the high-frequency amplifier is reduced over a wide dynamic range, and the channel temperature Can be suppressed.

In this embodiment, for simplicity, an FET for amplifying a signal is shown in a single-stage configuration. However, the present invention is not limited to this. It goes without saying that it can be applied.

In this embodiment, the directional coupler 2 is provided on the input side of the FET 4 to monitor the power P _{IN of the} input signal. However, the directional coupler is provided on the output side of the FET 4 to provide the output signal. of monitoring the power P _OUT, it may control the drain current V _d and the gate voltage V _g by the power control circuit in accordance with the level of the power P _OUT of the output signal.

[0037]

As described above, according to the present invention,
Since the drain current _Vd and the gate voltage _Vg, which are the bias voltage of the high-frequency amplifier, are independently controlled according to the power level of the input signal or the output signal, the amount of heat generated when the power of the input signal is small is reduced. Therefore, the increase in channel temperature can be suppressed.

Further, according to the present invention, even when the power of the input signal is small, the input / output characteristics of the high-frequency amplifier have substantially the same linearity as at the time of the fixed bias, and have almost the same gain as at the time of the fixed bias. As such, it can be used over a wide dynamic range and can be used for a wide range of applications.

[Brief description of the drawings]

FIG. 1 shows a circuit diagram of an embodiment of a high-frequency amplifier according to the present invention.

2 is a diagram showing changes in output characteristics of the FET in accordance with the drain voltage V _d.

3 is a diagram showing changes in output characteristics of the FET in accordance with the drain current I _d.

FIG. 4 shows a bias voltage and input / output characteristics in one embodiment of the high-frequency amplifier according to the present invention shown in FIG. 1,
(A) shows the power of the input RF signal and the bias voltage controlled by the power supply control circuit, that is, the drain voltage V
shows the relationship between _d and the gate voltage V _g, (b) the RF
This is an input / output characteristic of an FET that amplifies a signal.

Figure 5 shows the input-output characteristics of the high-frequency amplifier in the case of reducing the drain current I _d as the power P _IN of the input signal is reduced.

[Explanation of symbols]

 Reference Signs List 1 input terminal 2 directional coupler 3 power supply control circuit 4 FET 5 output terminal

Claims (1)

(57) [Claims] A power detection unit for detecting a power level of the input signal; an FET for amplifying the input signal; and a power level of the input signal being equal to or higher than a first predetermined value.
The drain voltage and gate voltage of the FET.
A constant value, and the power level of the input signal is
If the value is less than a predetermined value and is not less than a second predetermined value, the drain
The voltage is gradually reduced from the specified value within a predetermined range.
Together with the gate voltage to the specified value,
When the power level of the signal is less than the second predetermined value
When the drain voltage is set to a lower limit value of the predetermined range,
And a power supply control circuit for performing control to gradually reduce the gate voltage .