KR20040040099A - Circuit for Protecting Front-end of the Receiver in the Communication Equipments - Google Patents

Abstract

PURPOSE: A receiver input port protecting circuit in a communication equipment is provided to protect an input terminal from a high level external signal. CONSTITUTION: A first BPF(Band Pass Filter)(21) is formed to be alternately closed with a protecting circuit(22), so if a signal of above a bias voltage(Vbias) is received, it is totally reflected. The first BPF(21) is set to be turned to pass only a 5% band of a used center frequency to thereby prevent interference, and includes two inductors(L1,L2) and a first capacitor(C1). A matching circuit(23) matches the first and second BPFs(21,24) and includes three inductors(L3-L5). The second BPF(24) includes two inductors(L6,L7) and a second capacitor(C2). The protecting circuit(22) reflects or receives a signal introduced according to a switch ON/OFF of a BJT(Bipolar Junction Transistor)(Q1) and is performed even when power is OFF.

Description

Circuit for Protecting Front-end of the Receiver in the Communication Equipments

The present invention relates to a receiver input stage protection circuit in communication equipment, and more particularly, to a receiver input stage protection circuit in communication equipment to protect the input stage from an external signal flowing at a high level suitable for a transceiver of a VHF (Very High Frequency) communication equipment. will be.

In general communication equipment, the receiver input stage protection circuit may include the first and second TVS diodes 11 and 12, the general types of the first and second diodes 13 and 14, and a matching circuit (as shown in FIG. 1). 15) and LNA 16.

The two TVS diodes 11 and 12 are connected in parallel between the antenna and the LNA 16, that is, the anode side is connected by a signal line and the cathode side is connected to ground. In addition, the respective TVS diodes 11 and 12 are connected to the diodes 13 and 14 in series, respectively, to reduce the high capacitance of the TVS diodes 11 and 12.

In addition, the two TVS diodes 11 and 12 prevent a weak circuit from an electrical transient caused by electrostatic discharge, inductive load switching, or induced lightning. This is a device used for general purpose. It is generally referred to the maximum rating on the data sheet, that is, the peak pulse power, response time, surge rating, and the like. Appropriate TVS diodes 11 and 12 are selected and applied to the circuit.

In the two TVS diodes 11 and 12, the influx of voltages that damage the circuitry is avalanche operation or clamping of the silicon PN junction which reduces the magnitude of the voltage to such an extent that the circuit is not damaged. Is limited by).

Here, the waveforms limited by the TVS diodes 11 and 12 are as shown in FIG. 2, that is, FIG. 2 illustrates a case in which a transient peak voltage is applied to the TVS diodes 11 and 12. The waveform is shown and relates to a single power supply (+, GND) among DC power supplies.

As shown in FIG. 2, the rear end element is limited so as not to be destroyed, but in the case of a positive power supply (+, GND,-) and an AC line, as shown in FIG. 1, two TVS diodes 11 and 12 are shown. Is needed.

For example, when connected to the receiving end of a radio transceiver, it is an AC line, that is, only one half sine wave is applied when only one is connected, so the TVS diodes 11 and 12 must be connected in both directions. .

When the signal of LNA maximum rating level is introduced into the corresponding circuit input terminal, the corresponding TVS diodes 11 and 12 operate as protection circuits, and the positive half and negative half-waves pass through the respective TVS diodes 11 and 12. Energy is absorbed into the ground. In the following signals, the TVS diodes 11 and 12 do not perform the protection circuit operation and do not pass through the TVS diodes 11 and 12.

The TVS diodes 11 and 12 do not operate until a transient state occurs in the circuit, that is, when a general circuit operates, the breakdown voltage, which is an electrical characteristic of the TVS diodes 11 and 12, Standby current (i.e. leakage current), capacitance, etc. should not affect the operation of the general circuit in question, especially when applied to AC signal lines.

Here, the corresponding breakdown voltage is usually above 10 (%) of the reverse standoff voltage, which limits the stand-by current and is caused by the temperature coefficient of the corresponding TVS diodes 11 and 12. It is close to the Circuit Operating Voltage that allows the transition to the breakdown voltage.

On the other hand, if a transient occurs in the circuit, the TVS diodes 11 and 12 immediately limit the transient voltage to a safe voltage level called 'Clamping Voltage' and at the same time a potential circuit damage current. By inverting it prevents it from becoming any more protective element.

However, the high and nonlinear capacitance of the TVS diodes 11 and 12 deteriorates the linearity of the receiver input circuitry, which in turn reduces the available dynamic range of the receiver.

In addition, the TVS diodes 11 and 12 are directly connected to the receiver input terminal, and since the TVS diodes 11 and 12 may perform an operation of a protection circuit to an external frequency signal far away from the frequency band of the receiver. In this case, a limited signal is input to the receiver and at the same time the signal is retransmitted, i.e. reflected, into a wideband distorted signal, affecting other communication channels.

In other words, in the conventional receiver input protection circuit, the use of the TVS diode has a problem that the capacitance of the TVS diode deteriorates the linearity of the circuit, thereby reducing the usable dynamic range of the receiver. In addition, a large number of radio transceivers sharing the same frequency band are adjacent to each other with a minimum distance from each other, so that a high level transmitter output may destroy an internal circuit when an adjacent receiver is introduced into the adjacent receiver. There is also a problem.

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides a receiver input stage protection circuit suitable for a transceiver of a VHF communication equipment.

In addition, the present invention provides a receiver input stage protection circuit for protecting the input stage from the external signal flowing at a high level in the communication equipment, to solve the problem of the TVS diode used in the general receiver input stage protection circuit, an object thereof.

In addition, the present invention uses the receiver by using the BPF tuned to pass only a predetermined band of the center frequency of use and the load effect (load effect) in the portion of the signal input through the antenna in the receiver input terminal protection circuit of the communication equipment, Its purpose is to prevent the ingress of signals in other distant frequency bands without affecting the possible dynamic range.

In addition, the present invention can not only perform the protection circuit operation when the power is off, except when there is no signal flowing through the antenna in the receiver input terminal protection circuit of the communication equipment, the corresponding inflow during the protection circuit operation The purpose is to reflect the signal as it is without distortion.

1 is a block diagram illustrating a receiver input stage protection circuit in a general communication equipment.

FIG. 2 is a diagram illustrating waveforms clamped by a TVS diode in FIG. 1.

3 is a block diagram illustrating a receiver input stage protection circuit in communication equipment according to an exemplary embodiment of the present invention.

FIG. 4 is a diagram illustrating a waveform of a voltage applied to a first capacitor and a waveform of a current flowing through a pin diode in FIG. 3.

Explanation of symbols on the main parts of the drawings

21, 24: BPF (Band Pass Filter) 22: protection circuit

23: Matching Circuit

25: Low Noise Amplifier (LNA) Q1: Bipolar Junction Transistor (BJT)

R1, R2: Resistor L1 ~ L7: Inductor

C1 ~ C4: Capacitor D1: Pin Diode

D2: Diode Vbias: Bias Voltage

In the communication equipment according to the embodiment of the present invention for achieving the above object, the receiver input stage protection circuit is connected in two stages between the antenna and the first stage amplifier in the communication equipment, and a short circuit occurs when an excessive signal of more than a bias voltage is introduced. BPF for total reflection of the incoming signal by the state; A matching circuit unit for matching the two BPFs with each other; It is connected to the first stage of the BPF of the two stages, it characterized in that it comprises a protection circuit for allowing the current to flow to the ground and the short circuit with the first stage BPF when the incoming signal is an excessive signal of more than the bias voltage.

Preferably, the first stage BPF has two inductors, and the voltage of the incoming signal is applied to the inductor connected to the protection circuit due to an AC short circuit with the protection circuit, and the input impedance has a pure inductance. And total reflection of the incoming signal without distortion.

Also preferably, the first stage BPF may be tuned to pass only a predetermined band of the center frequency of use, thereby preventing a signal from another frequency band far from being introduced.

Further preferably, the protection circuit unit includes a pin diode which, when an excessive signal exceeding the bias voltage flows through the first stage BPF, forms a path so that the current flows to a resistor connected to the ground by the inflow signal; A diode for rectifying the voltage signal across the resistor; And a BJT which is turned on by the voltage signal rectified by the diode to lower the collector voltage to lower the bias voltage applied to the pin diode so as to be in short circuit with the first BPF. Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

In the communication equipment according to the embodiment of the present invention, as shown in FIG. 3, the receiver input stage protection circuit includes two stages of BPFs 21 and 24, a protection circuit unit 22, a matching circuit unit 23, and a first stage. LNA 25 is made.

The two stages BPFs 21 and 24 are connected between the antenna and the LNA 25 of the first stage, and are inductive coupled BPFs. The capacitors C1 and C2 and the high queue Q value are used. And low power consumption inductors (L1 to L7).

In addition, the first BPF 21 is configured to be short-circuit alternatingly with the protection circuit 22 so that the signal is totally reflected when an excessive signal of more than the bias voltage Vbias is introduced, ie, due to a short-circuit state. Most of the signal voltage is applied to one inductor L1, and the short circuit condition causes the input impedance to have pure inductance so that almost all of the signal is totally reflected without distortion, and this state is used as the BJT (Q1) of the protection circuit section 22. Is maintained until an input signal is introduced that does not switch on.

In addition, the first BPF 21 is set to be tuned so as to pass only 5 (%) band of the center frequency of use, thereby preventing signal inflow, that is, interference from other frequency bands, which are far from each other. L2 and a first capacitor C1, for example, the first inductor L1 has a value of 500 nH and the second inductor L2 has a value of 300 nH and the first Capacitor C1 has a value of 30 to 300 pF. The inductors L1 and L2 have a high cue value in order to prevent the inflow of external signals, and the power consumption is low because the loss of the first stage of the receiver is directly connected to the increase in the noise figure.

The matching circuit unit 23 matches the first BPF 21 and the second BPF 24 with each other, and includes three inductors L3 to L5. For example, the matching third inductor L3 and the third inductor L3 and L5 are formed. The fifth inductor L5 has a value of 110 (nH) and the fourth inductor L4 has a value of 5 (nH).

The second BPF 24 includes two inductors L6 to L7 and a second capacitor C2. For example, the sixth inductor L6 has a value of 500 nH and the seventh inductor L7. ) Has a value of 300 (nH) and the second capacitor (C2) has a value of 30 ~ 300 (pF).

The protection circuit part 22 is connected to the first BPF 21 and reflects or introduces an incoming signal according to the switch on / off of the BJT Q1, and the bias voltage Vbias when the power is turned off. ) Is 0 (V), so the protection circuit operates even when the power is off.

The protection circuit 22 includes a pin diode D1, a BJT Q1, a general diode D2, two resistors R1 and R2, two capacitors C3 and C4, and a bias. For example, the first resistor R1 has a value of 10 (Ω), the second resistor R2 has a value of 10 (KΩ), and the third capacitor C3 has a value of 10 (Ω). The fourth capacitor C4 has a value of pF) and a value of 1 (pF).

The path through which the current flows out to the first resistor R1 connected to the ground when the pin diode D1 is forward biased and an excessive signal exceeding the bias voltage Vbias is introduced using a property of passing the signal. It plays a role in creating a.

The BJT Q1 and the diode D2 allow more current to flow to the ground through the first resistor R1 in order to be in a short circuit in alternating state with the first BPF 21. That is, the diode D2 rectifies the voltage signal to apply the rectified voltage signal to the corresponding BJT (Q1) to turn on the corresponding BJT (Q1), and the corresponding BJT (Q1) turns on the diode D2. By lowering the collector voltage by lowering its collector voltage and lowering the bias voltage Vbias applied to the corresponding pin diode D1, more signals are introduced and current flows through the first resistor R1. As it exits, the first BPF 21 and the AC is short circuited.

The bias voltage Vbias is reversed so as to be a forward bias.

Referring to the operation of the receiver input terminal protection circuit in the communication equipment according to an embodiment of the present invention.

First, when the signal flowing into the receiver input terminal is an excessive signal equal to or greater than the bias voltage Vbias, the signal flows into the protection circuit unit 22 via the first BPF 21. The waveform of the voltage across one capacitor C1 is shown in FIG. 4.

Accordingly, the pin diode D1 in the protection circuit unit 22 has a property of passing a signal only when it is forward biased, and is conducted by an excessive signal of more than a bias voltage Vbias flowing through the first BPF 21. The current flows out to the ground through the first resistor R1 in the protection circuit unit 22. At this time, the waveform of the current flowing through the pin diode (D1) is as shown in FIG.

In addition, the diode D2 in the protection circuit unit 22 rectifies the voltage signal across the first resistor R1 and applies the rectified voltage signal to the BJT Q1 in the protection circuit unit 22. Switch on the BJT (Q1).

Accordingly, the BJT Q1 is switched on by the rectified voltage signal applied from the diode D2 so that current flows through the BJT Q1, thereby lowering its collector voltage and thereby the The reverse bias applied to the pin diode D1 is lowered.

Then, more signals are introduced due to the lower reverse bias, so that the BJT (Q1) is more conductive so that current flows to ground through the first resistor (R1), whereby the first BPF (21) In exchange for the short circuit state.

As a result, the first BPF 21 is short-circuit in alternating state with the protection circuit 22, so that most of the voltage signals flowing into the first BPF 21 are mostly inducted from the first inductor in the first BPF 21. In this case, since the input impedance of the first inductor L1 substantially has a pure inductance component, almost the entire incoming voltage signal is totally reflected without distortion.

This state is maintained until the input signal of the BJT Q1 in the protection circuit section 22 is switched on, i.e., cannot be conducted.

In addition, even when the power is turned off, since the bias voltage Vbias is 0 (V), the protection circuit operation of the protection circuit unit 22 is continued even when the power is turned off.

On the other hand, when there is no voltage signal flowing into the first BPF 21, the protection circuit operation of the protection circuit unit 22 is not performed.

In addition, when the BJT Q1 in the protection circuit unit 22 is cut-off, the load effect of the first BPF 21 is insignificant, that is, the cue value is '100'. Since it exceeds 1 and 2 (pF), it is not enough to affect the dynamic range of the receiver.

As described above, the present invention provides an appropriate receiver input stage protection circuit to a transceiver of the VHF communication equipment to protect the input stage from external signals flowing at a high level. In addition, the present invention does not affect the available dynamic range of the receiver by using the BPF, and prevents the inflow of signals in other frequency bands far away, and protects even when the power is turned off except when there is no corresponding inflow signal. In addition to performing the circuit operation, it is possible to reflect the incoming signal as it is without distortion during the protection circuit operation.

Claims (3)

A band pass filter (BPF) connected between the antenna and the first stage amplifier in communication equipment and totally reflecting the inflow signal due to a short circuit when an excessive signal over a bias voltage is introduced; A matching circuit unit for matching the two BPFs with each other; A communication circuit connected to the first stage of the BPFs of the two stages and including a protection circuit which causes the current to flow to ground when the incoming signal is an excessive signal of a bias voltage or more, so that the first stage BPF is short-circuited. Receiver input stage protection circuit in equipment. According to claim 1, The first stage BPF has two inductors, and due to an alternating short circuit with the protection circuit portion, the voltage of the inflow signal is applied to the inductor connected to the protection circuit portion, and the input impedance has a pure inductance so that the inflow Receiver input stage protection circuit in a communication equipment, characterized in that the signal is totally reflected without distortion. According to claim 1, The protection circuit unit may include a pin diode which, when an excessive signal exceeding the bias voltage flows through the first BPF, forms a path so that current flows to a resistor connected to the ground by being connected by a corresponding inflow signal; A diode for rectifying the voltage signal across the resistor; And a bipolar junction transistor (BJT) that is turned on by the voltage signal rectified by the diode to lower the collector voltage to lower the bias voltage applied to the pin diode so that the diode is short-circuited with the first BPF. A receiver input stage protection circuit in a telecommunication equipment.