A radio frequency amplifier protection circuit

Abstract

The utility model relates to radio frequency amplifier technical field especially relates to a radio frequency amplifier protection circuit, including triode Q1 and Q2, the triode Q1 and Q2's emitting electrode is coupled and has voltage source VCC in common external, the triode Q1 and Q2's collector is coupled and has current source ISS in common external, the triode Q1's base is coupled with diode D1, diode D1's negative pole is coupled with diode D3, diode D3's positive pole is coupled with the triode Q2's base, the utility model discloses through diode D1 to D6 to the overvoltage protection of input differential pair tube, at this time, if the voltage difference between two input terminals is applied and exceeds the conduction voltage (0.7V) of PN junction, diode D1 or D2 will be turned on, and the input signal flow is made to flow between two input terminals, reaches the purpose of protecting radio frequency amplifier input differential pair tube.

Description

Technical Field

[0001] This utility model relates to the field of radio frequency amplifier technology, and in particular to a radio frequency amplifier protection circuit. Background Technology

[0002] When the input terminal of an RF amplifier is subjected to an excessively large input voltage, or even if the voltage exceeds the power supply voltage of the RF amplifier, the RF amplifier is highly likely to be damaged by a large injected current. Although the large input current caused by input overvoltage can be effectively limited by connecting a resistor in series with the input terminal, this resistor will greatly increase the equivalent input noise voltage.

[0003] Therefore, it is necessary to design an input overvoltage protection circuit that can change its resistance value according to the operating state of the RF amplifier. When the RF amplifier experiences input overvoltage, the protection circuit provides a high resistance value to limit the input current. When the RF amplifier is operating normally, the resistance of the protection circuit can be ignored. To this end, we propose an RF amplifier protection circuit to solve this problem. Utility Model Content

[0004] To address the shortcomings of existing technologies, this utility model provides a protection circuit for an RF amplifier, which solves the technical problem that "when the input terminal of an RF amplifier is subjected to an excessively large input voltage, or even if the voltage exceeds the power supply voltage of the RF amplifier, the RF amplifier is highly likely to be damaged by a large injected current. Although the large input current caused by input overvoltage can be effectively limited by connecting a resistor in series on the input terminal, this resistor will greatly increase the equivalent input noise voltage."

[0005] To achieve the above objectives, this utility model provides the following technical solution:

[0006] A radio frequency amplifier protection circuit includes transistors Q1 and Q2. The collectors of transistors Q1 and Q2 are coupled to each other via current-limiting resistors RC1 and RC2, respectively. A voltage source VCC is externally connected to both current-limiting resistors RC1 and RC2. The emitters of transistors Q1 and Q2 are coupled to each other and are externally connected to a current source ISS. A diode D1 is coupled to the base of transistor Q1 via a current-limiting resistor RB1. A diode D3 is coupled to the cathode of diode D1. The anode of diode D3 is coupled to the base of transistor Q2 via a current-limiting resistor RB2. A diode D4 is coupled to the base of transistor Q2 via a current-limiting resistor RB2. A diode D2 is coupled to the anode of diode D4. The cathode of diode D2 is coupled to the base of transistor Q1 via a current-limiting resistor RB1. The bases of transistors Q1 and Q2 are coupled to an input VINP and an output VINN, respectively, via a current-limiting component.

[0007] As a preferred embodiment of this invention, the current limiting component at the base of transistor Q1 includes field-effect transistors J1 and J2, the sources of which are coupled to each other and connected to the base of transistor Q1 via a current-limiting resistor RB1.

[0008] As a preferred embodiment of the present invention, the current limiting component at the base of the transistor Q2 includes field-effect transistors J3 and J4, the sources of which are coupled to each other and coupled to the base of the transistor Q2 via a current-limiting resistor RB2.

[0009] As a preferred embodiment of this invention, the current limiting component at the base of the transistor Q1 is a resistor R1.

[0010] As a preferred embodiment of this invention, the current limiting component at the base of the transistor Q2 is a resistor R2.

[0011] This utility model provides a radio frequency amplifier protection circuit, which has the following beneficial effects:

[0012] In this invention, field-effect transistors J1, J2, J3, and J4 are all P-channel depletion-type JFET devices. When the RF amplifier operates within the specified voltage range, the input bias current of the RF amplifier flows through the JFET device. At this time, the channel of the JFET device is in the conducting state and can be regarded as a resistor with a very low resistance value. The actual resistance value is about 1 milliohm, which can minimize capacitance and leakage.

[0013] In this invention, diodes D1-D4 are used for overvoltage protection of the input differential pair transistors. If the voltage difference applied between the two input terminals exceeds the forward voltage of the PN junction (0.7V), diode D1 or D2 will conduct, allowing the input signal to flow between the two input terminals, thereby protecting the input differential pair transistors of the RF amplifier. Attached Figure Description

[0014] Figure 1 This is a circuit diagram of Embodiment 1 of the present invention;

[0015] Figure 2 This is a circuit diagram of Embodiment 2 of the present invention. Detailed Implementation

[0016] To make the technical problems, technical solutions, and beneficial effects of this utility model clearer, the present utility model will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present utility model and are not intended to limit the present utility model.

[0017] Therefore, a feature pointed out in this specification is used to describe one feature of one embodiment of the present invention, and does not imply that every embodiment of the present invention must have the described feature. Furthermore, it should be noted that this specification describes many features. Although certain features may be combined to illustrate possible system designs, these features may also be used in other combinations not explicitly stated. Therefore, unless otherwise stated, the described combinations are not intended to be limiting.

[0018] The principle and structure of this utility model will be described in detail below with reference to the accompanying drawings and embodiments: Example

[0019] refer to Figure 1 A radio frequency amplifier protection circuit includes transistors Q1 and Q2. The collectors of transistors Q1 and Q2 are coupled to each other via current-limiting resistors RC1 and RC2, respectively. Current-limiting resistors RC1 and RC2 are connected to an external voltage source VCC. The emitters of transistors Q1 and Q2 are coupled to each other and are connected to an external current source ISS. The base of transistor Q1 is coupled to a diode D1 via a current-limiting resistor RB1. The cathode of diode D1 is coupled to a diode D3. The anode of diode D3 is coupled to the base of transistor Q2 via a current-limiting resistor RB2. The base of transistor Q2 is coupled to a diode D4 via a current-limiting resistor RB2. The anode of diode D4 is coupled to a diode D2. The cathode of diode D2 is coupled to the base of transistor Q1 via a current-limiting resistor RB1. The bases of transistors Q1 and Q2 are coupled to an input VINP and an output VINN, respectively, via a current-limiting component.

[0020] Furthermore, the current limiting component at the base of transistor Q1 includes field-effect transistors J1 and J2, the sources of which are coupled to each other and connected to the base of transistor Q1 via a current-limiting resistor RB1; the current limiting component at the base of transistor Q2 includes field-effect transistors J3 and J4, the sources of which are coupled to each other and connected to the base of transistor Q2 via a current-limiting resistor RB2.

[0021] Among them, field-effect transistors J1, J2, J3, and J4 are all P-channel depletion-type JFET devices. When the RF amplifier operates within the specified voltage range, the input bias current of the RF amplifier flows through the JFET device. At this time, the channel of the JFET device is in the on state and can be regarded as a resistor with a very low resistance value, with an actual resistance value of about 1 milliohm.

[0022] A normally functioning RF amplifier has a very low input bias current. No matter how high the gate-drain voltage difference is, the conductive channel of the JFET device will not be shut off. If the common-mode input voltage VIN of the RF amplifier exceeds the voltage drop of a diode in the power supply, a large input current will flow through the JFET device, causing the channel to be pinched off. Its equivalent resistance will increase exponentially, eventually causing the input differential pair transistors to be subjected to a large current injection due to overvoltage. Example

[0023] refer to Figure 2 The difference between Embodiment 2 and Embodiment 1 is that the current limiting component at the base of transistor Q1 is resistor R1, and the current limiting component at the base of transistor Q2 is resistor R2. By setting resistors R1 and R2, the magnitude of the current is limited, thereby reducing the noise generated by the amplifier.

[0024] The above description is merely a specific embodiment of this utility model, but the protection scope of this utility model is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this utility model, and these modifications or substitutions should all be covered within the protection scope of this utility model. Therefore, the protection scope of this utility model should be determined by the scope of the claims.

Claims

1. A radio frequency amplifier protection circuit, comprising transistors Q1 and Q2, characterized in that, The collectors of transistors Q1 and Q2 are coupled to each other via current-limiting resistors RC1 and RC2, respectively. A voltage source VCC is connected to both current-limiting resistors RC1 and RC2. The emitters of transistors Q1 and Q2 are coupled to each other and are connected to a current source ISS. The base of transistor Q1 is coupled to diode D1 via current-limiting resistor RB1. The cathode of diode D1 is coupled to diode D3. The anode of diode D3 is coupled to the base of transistor Q2 via current-limiting resistor RB2. The base of transistor Q2 is coupled to diode D4 via current-limiting resistor RB2. The anode of diode D4 is coupled to diode D2. The cathode of diode D2 is coupled to the base of transistor Q1 via current-limiting resistor RB1. The bases of transistors Q1 and Q2 are coupled to the input VINP and output VINN, respectively, via current-limiting components.

2. The radio frequency amplifier protection circuit according to claim 1, characterized in that, The current limiting component at the base of transistor Q1 includes field-effect transistors J1 and J2, the sources of which are coupled to each other and connected to the base of transistor Q1 via a current-limiting resistor RB1.

3. The radio frequency amplifier protection circuit according to claim 1, characterized in that, The current limiting component at the base of transistor Q2 includes field-effect transistors J3 and J4, the sources of which are coupled to each other and connected to the base of transistor Q2 via a current-limiting resistor RB2.

4. The radio frequency amplifier protection circuit according to claim 1, characterized in that, The current limiting component at the base of the transistor Q1 is a resistor R1.

5. The radio frequency amplifier protection circuit according to claim 1, characterized in that, The current limiting component at the base of the transistor Q2 is resistor R2.

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