JPH09199950A - Protection circuit for amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To protect a power amplifier consisting of a FET from being destroyed due to an increased drain current caused by an increase in an input signal level or the like. SOLUTION: When a signal level from a terminal 2 is increased and a drain current of a power amplifier 1 is increased, a drain current detection section 5 detects an increase in the drain current based on a voltage drop across a resistor 4, a gain voltage control section 6 controls a gate voltage of the power amplifier 1 via a loop filter 7 to suppress the increase in the drain current. In the case that the drain current is increased regardless of the control of the gate voltage control section 6 and the signal level from the drain current detection section 5 is larger than a reference voltage 9, an output signal level from a comparator 8 goes to 'H' and the signal is fed to a switch circuit 3 via a latch circuit 10 to switch off the circuit 3. The latch circuit 10 is reset by a required reset signal 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an overcurrent protection circuit for a power amplifier using a field effect transistor (FET), in which the drain current increases as the input signal level increases,
The present invention relates to a device that prevents a FET from being destroyed.

[0002]

2. Description of the Related Art When a power amplifier used in an output stage of a wireless communication device is constructed by using FETs, the output signal level of the amplifier in the preceding stage is increased due to a decrease in ambient temperature or the like, or noise is mixed in the power amplifier to cause a problem. The input signal level becomes excessive, which increases the drain current, which may lead to breakdown. In addition, when the gate voltage of the power amplifier is generated as a negative voltage from a required positive voltage power source and divided by a suitable resistor to be applied to the required voltage, an abnormality (fault, etc.) occurs in the circuit that generates this negative voltage. If it occurs, the gate voltage becomes 0 V, an excessive drain current flows, and the power amplifier is destroyed.

[0003]

In view of the above, the present invention detects the drain current of the power amplifier and controls the gate voltage of the power amplifier according to the drain current value, or the drain current is equal to or more than a required value. When the power supply voltage increases, the drain power supply is shut off to prevent damage to the power amplifier.

[0004]

In order to solve the above-mentioned problems, the present invention is based on a resistor inserted between a drain terminal and a drain power source of a power amplifier using an FET and a voltage drop of the resistor. A drain current detection unit that detects the drain current of the power amplifier, and a gate voltage control unit that controls the gate voltage of the power amplifier based on a signal from the drain current detection unit and suppresses an increase in the drain current, or A comparator that compares the signal from the drain current detection unit with a required reference voltage and outputs a signal when it is higher than the reference voltage, a latch circuit that latches the signal from the comparator, and a resistor connected in series with the resistor. The present invention provides a protection circuit for an amplifier, which is provided with a switch circuit which is inserted and opened by a signal from a latch circuit.

[0005]

With the above construction, in the amplifier protection circuit according to the present invention, the output signal level of the amplifier at the preceding stage increases due to a decrease in ambient temperature or the input signal level of the power amplifier is increased due to the inclusion of noise. When the drain current increases due to the increase, the gate voltage of the power amplifier is controlled based on the signal from the drain current detector to suppress the increase of the drain current, thereby protecting the power amplifier from breakdown. Alternatively, when the gate voltage (negative voltage) is generated from a required positive voltage power source, an abnormality occurs in the negative voltage generation circuit, the gate voltage becomes 0 V, and the drain current increases and becomes equal to or higher than the required reference level. , The switch circuit inserted in the drain power supply is opened, and the drain power supply is shut off.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an amplifier protection circuit according to the present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram of a main part of an embodiment of an amplifier protection circuit according to the present invention. In the figure, 1 is a power amplifier (PA), which is composed of an FET and amplifies a signal from a terminal 2, for example, a final circuit of a radio communication device which outputs a high frequency power of about 200 mW at about 2.4 GHz. Is. 3 is a switch circuit, 4 is a resistor, the switch circuit 3 and the resistor 4 are connected in series between the drain power supply Vdd and the drain terminal D of the power amplifier 1, and the switch circuit 3 is normally turned on. The resistor 4 is for detecting the drain current (Id) of the power amplifier 1, and is set to a sufficiently small value so as not to hinder the supply of the drain voltage required for the power amplifier 1. 5
Is a drain current detection unit that detects the drain current (Id) of the power amplifier 1 based on the voltage drop of the resistor 4. 6
Is a gate voltage control unit that generates a gate voltage (Vgs) of the power amplifier 1 based on a signal from the drain current detection unit 5 and applies it to the gate terminal G of the power amplifier 1 via the loop filter 7. Reference numeral 8 is a comparator, which is a drain current detection unit 5
The level of the signal is compared with the required reference voltage 9 and the signal is output when the level is higher than the reference voltage 9. A latch circuit 10 latches a signal from the comparator 9 and applies this signal to the switch circuit 3 to turn it off. The latch circuit 10
Is released by a reset signal 11 by a required operation.

FIG. 2 is a block diagram of essential parts of another embodiment of the amplifier protection circuit according to the present invention. In the figure, reference numeral 21 denotes a gate voltage generator, which generates a gate voltage Vgs from a positive voltage from a power source Vdd '(which is always supplied) different from the drain power source Vdd (which is supplied only when transmitting), It is supplied to the gate terminal G of the power amplifier 1. The other reference numerals are the same as those in FIG. 1, and therefore their explanations are omitted.

Next, the operation of the protection circuit for the amplifier according to the present invention will be described. First, in the case of FIG. 1, the power amplifier 1 is FE
If the signal level input from the terminal 2 is within the set range, the drain power supply Vdd is connected to the drain terminal D, and the gate terminal is connected. The voltage Vgs applied to G (for example,
Drain current Id (for example, 250m
A) flows. However, when the signal level from the amplifier at the previous stage input to the terminal 2 is increased due to a decrease in ambient temperature or the noise is added to the input signal to increase the level, the drain current is increased, and the drain current is increased between both ends of the resistor 4. Voltage rises. This increase in voltage is detected by the drain current detection unit 5, and the gate voltage control unit 6 increases the gate voltage Vgs of the power amplifier 1 in the negative direction based on the signal from the drain current detection unit 5 and decreases the drain current. Thus, the increase of the drain current Id is suppressed and the power amplifier 1 is prevented from being destroyed.

The above-mentioned control of the gate voltage cannot suppress the increase of the drain current, the voltage across the resistor 4 rises, the signal level output from the drain current detector 5 rises, and this level becomes the reference voltage. When it becomes higher than 9, the output signal level of the comparator 8 becomes "H", this signal is latched by the latch circuit 10, applied to the switch circuit 3 and turned off, and the drain power supply of the power amplifier 1 is cut off. Then
Prevent destruction.

In the case of FIG. 2, when the gate voltage generator 21 becomes abnormal and a negative voltage is not generated and the gate voltage Vgs of the power amplifier 1 becomes 0 V, the drain current Id becomes excessive and the resistor 4 The voltage drop of will rise. In this case, similarly to the above, the signal level input to the comparator 8 from the drain current detection unit 5 increases, becomes higher than the reference voltage 9, and the output signal level of the comparator 8 becomes “H”. This signal is latched by the latch circuit 10 and applied to the switch circuit 3 to turn it off, thereby cutting off the drain power source of the power amplifier 1 and preventing destruction. The latch circuit 10 is reset by the reset signal 11 output by a required operation, and returns the switch circuit 3 to the ON state.

[0011]

As described above, according to the amplifier protection circuit of the present invention, the output signal level of the pre-stage amplifier increases due to a decrease in ambient temperature, or the input signal level of the power amplifier increases due to noise. When the drain current increases, the gate voltage of the power amplifier is controlled according to the increase of the drain current to suppress the increase of the drain current, and the control of the gate voltage cannot suppress the increase of the drain current. When the drain current increases or the gate voltage of the power amplifier becomes 0V due to a failure of the gate voltage generator, and an excessive drain current flows, the switch circuit inserted in the drain power supply path is shut off. Therefore, it is useful because it can protect the power amplifier from damage.

[Brief description of drawings]

FIG. 1 is a block diagram of a main part of an embodiment of a protection circuit for an amplifier according to the present invention.

FIG. 2 is a block diagram of a main part of another embodiment of a protection circuit for an amplifier according to the present invention.

FIG. 3 is an example of a transfer characteristic of an FET that constitutes a power amplifier.

[Explanation of symbols]

 1 power amplifier (composed of FET) 3 switch circuit 4 resistor 5 drain current detection unit 6 gate voltage control unit 7 loop filter 8 comparator 9 reference voltage 10 latch circuit 11 reset signal 21 gate voltage generation unit

Claims (5)

[Claims] 1. A resistor inserted between a drain terminal and a drain power source of a power amplifier using a field effect transistor, and a drain current detection unit for detecting a drain current of the power amplifier based on a voltage drop of the resistor. , A gate voltage control unit that controls the gate voltage of the power amplifier based on a signal from the drain current detection unit and suppresses an increase in the drain current. 2. A resistor inserted between a drain terminal and a drain power source of a power amplifier using a field effect transistor, and a drain current detection unit for detecting the drain current of the power amplifier based on the voltage drop of the resistor. , A comparator for comparing the signal from the drain current detector with a required reference voltage and outputting a signal when it is higher than the reference voltage, a latch circuit for latching the signal from the comparator, and the resistor connected in series An amplifier protection circuit consisting of a switch circuit that is opened by a signal from the latch circuit. 3. A resistor inserted between a drain terminal and a drain power source of a power amplifier using a field effect transistor, and a drain current detection unit for detecting the drain current of the power amplifier based on the voltage drop of the resistor. A gate voltage control unit that controls the gate voltage of the power amplifier based on a signal from the drain current detection unit and suppresses an increase in the drain current, and compares the signal from the drain current detection unit with a required reference voltage, A comparator that outputs a signal when the voltage is higher than the reference voltage, a latch circuit that latches the signal from the comparator, and a switch circuit that is connected in series with the resistor and that is opened by the signal from the latch circuit are provided. A protection circuit for an amplifier, wherein the switch circuit is activated when the drain current still increases under the control of the gate voltage control unit. 4. The resistor does not hinder the voltage applied to the drain terminal during normal operation of the power amplifier,
An amplifier protection circuit according to claim 1, 2 or 3, which is set to a value necessary for detecting the drain current. 5. The amplifier protection circuit according to claim 2, wherein the latch circuit is reset by a required reset signal.