A common mode rejection circuit dedicated to a telephone line

Abstract

The utility model discloses a telephone line special common mode rejection circuit relates to communication anti -interference technical field, and this circuit passes through the synergic design of triode bias circuit, common mode inductance and direct -current capacitor, realizes three major functions: one is high -efficient suppression high -frequency common mode interference signal (the path of conversion into differential mode interference is blocked) ;Two is to provide direct current passage for telephone line to transmit feed current, three is to provide alternating current passage for low -frequency ringing signal. Meanwhile, the circuit has very small transmission influence to differential mode audio signal, can be directly connected in series in ordinary telephone communication equipment, makes it adapt strong interference scene (such as mechanical and electrical equipment, broadcast transmitting station nearby), and the call quality stability is obviously promoted.

Description

Technical Field

[0001] This utility model relates to the field of communication anti-interference technology, and in particular to a common-mode suppression circuit for telephone lines. Background Technology

[0002] Telephone lines, as a traditional communication carrier, can transmit over distances of up to 5 kilometers, often passing through areas with strong electromagnetic interference, such as electromechanical equipment and broadcasting stations. If common-mode interference signals (such as high-frequency electromagnetic radiation) are not effectively suppressed, they will be converted into differential-mode signals and superimposed on the effective telephone signals (such as audio, power supply current, and ringing signals), resulting in call noise, signal attenuation, or even communication interruption.

[0003] Existing telephone line interference suppression solutions have the following shortcomings:

[0004] While simply using filter capacitors or circuits can suppress common-mode interference, it will block the DC path (affecting power supply) or low-frequency ringing signals (causing ringing failure).

[0005] General-purpose anti-interference circuits cannot simultaneously achieve "common-mode rejection" and "differential-mode signal transmission", which can easily lead to audio signal attenuation and reduced call quality;

[0006] It is sensitive to line polarity, requiring differentiation between the positive and negative terminals of the telephone line, which makes actual installation inconvenient.

[0007] Therefore, a dedicated circuit needs to be designed that can simultaneously meet the requirements of "high-efficiency common-mode rejection, ensuring DC / low-frequency path, no polarity requirement, and no impact on audio transmission". Summary of the Invention

[0008] In order to overcome the shortcomings of the prior art, this application proposes a common-mode suppression circuit specifically for telephone lines to solve the problems existing in the prior art.

[0009] To solve the above-mentioned technical problems, this utility model provides the following technical solution:

[0010] A common-mode rejection circuit for telephone lines includes a transistor Q1, resistors R1, R2, and R3, a capacitor C1, lines L1 and L4, and a rectifier bridge D1. Resistor R2, in parallel with capacitor C1, and then in series with resistor R1 form the bias circuit for transistor Q1. The collector of transistor Q1 is connected to line L4 through resistor R3. The rectifier bridge D1 is connected between TIP_A and TIP_B terminals to adapt the polarity of the TIP terminals.

[0011] The lower half of the circuit includes transistor Q2, resistor R4, resistor R5, resistor R6, capacitor C4, lines L2 and L3, and rectifier bridge D2; resistor R5 is connected in parallel with capacitor C4 and then in series with resistor R4 to form the bias circuit of transistor Q2. The collector of transistor Q2 is connected to line L3 through resistor R6. Rectifier bridge D2 is connected between resistor RING_A and resistor RING_B to adapt the polarity of resistor RING.

[0012] The intermediate coupling circuit includes a common-mode line T1 and DC blocking capacitors C2 and C3. The input terminal of the common-mode line T1 is connected to L4 of the upper half circuit and L3 of the lower half circuit, respectively, and the output terminal is connected to TIP_B and resistor RING_B through DC blocking capacitors C2 and C3, respectively.

[0013] As a further technical solution of this utility model: in the upper circuit, the resistance value of resistor R3 is less than that of resistors R1 and R2, the resistance values ​​of resistors R1 and R2 are on the same order of magnitude, and the capacitance value of capacitor C1 is ≥1μF; in the lower circuit, the resistance value of resistor R6 is less than that of resistors R4 and R5, the resistance values ​​of resistors R4 and R5 are on the same order of magnitude, and the capacitance value of capacitor C4 is ≥1μF.

[0014] As a further technical solution of this utility model: the transistor Q1 is an NPN transistor.

[0015] As a further technical solution of this utility model: the transistor Q2 is an NPN transistor.

[0016] As a further technical solution of this utility model: the transistors Q1 and Q2 are low-frequency, low-power transistors with a withstand voltage ≥25V and a gain β=50-100.

[0017] One or more technical solutions provided in the embodiments of this application have at least the following technical effects or advantages:

[0018] 1. Strong common-mode rejection capability: The common-mode interference rejection ratio above 1MHz is ≥60dB, significantly reducing the risk of differential-mode interference conversion;

[0019] 2. Good signal compatibility: DC power supply (below 50mA) transmission voltage drop <0.3V, low frequency ringing signal (20Hz) transmission efficiency ≥95%, audio signal (300Hz-3400Hz) attenuation ≤0.5dB;

[0020] 3. Non-polarity design: The rectifier bridge adapts to any polarity of the TIP / resistor RING terminal, eliminating the need to distinguish between positive and negative terminals during installation;

[0021] 4. Wide applicability: It can be directly connected in series with ordinary telephone communication equipment, making it suitable for strong interference scenarios such as electromechanical equipment and broadcasting stations, without the need to modify the original equipment. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the overall circuit structure of the present invention. Detailed Implementation

[0023] The technical solutions in the embodiments of this utility model will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this utility model, and not all embodiments. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this utility model.

[0024] like Figure 1 As shown, a common-mode rejection circuit for telephone lines includes an upper circuit, a lower circuit, and an intermediate coupling circuit, with the specific structure as follows:

[0025] Upper half of the circuit (TIP terminal path):

[0026] This includes transistor Q1, resistors R1-R3, capacitor C1, inductors L1 and L4, and rectifier bridge D1;

[0027] Bias circuit: Resistor R2 is connected in parallel with capacitor C1 and then in series with resistor R1 to form the bias circuit of transistor Q1, providing bias voltage Vb≈(Vin-Vout)×(resistor R2 / / capacitor C1) / (resistor R1+(resistor R2 / / capacitor C1)).

[0028] Impedance characteristics: Through parameter design (resistor R3 has a small resistance value, resistors R1 and R2 have large resistance values ​​and are of the same order of magnitude, and capacitor C1 has a large capacitance value), the path from L1 to L4 exhibits the characteristics of "large AC impedance and small DC impedance" (high-frequency common-mode signals are blocked, while DC and low-frequency signals can pass through).

[0029] Non-polarity design: Rectifier bridge D1 ensures that TIP_A and TIP_B terminals can work normally regardless of polarity.

[0030] Lower half of the circuit (resistor ring terminal is open):

[0031] The structure is the same as the upper part, including transistor Q2, resistors R4-R6, capacitor C4, inductors L2 and L3, and rectifier bridge D2;

[0032] Function: To achieve a path from L2 to L3 with "high AC impedance and low DC impedance", and to work with rectifier bridge D2 to meet the non-polarity requirement of resistor RING_A and resistor RING_B, ensuring DC power supply and low-frequency ringing signal transmission, and blocking high-frequency common-mode interference.

[0033] Intermediate coupling circuit:

[0034] This includes common-mode inductor T1 and DC blocking capacitors C2 and C3;

[0035] Common-mode inductor T1: It has a large inductance value and presents high impedance to common-mode interference signals (blocking their flow) and low impedance to differential-mode audio signals (allowing transmission).

[0036] DC blocking capacitors C2 and C3: These have relatively large capacitance values, providing a path for differential-mode audio signals while isolating the DC component from the common-mode inductor.

[0037] Working principle:

[0038] Common-mode interference suppression: When a high-frequency common-mode signal passes through the TIP terminal and the RING terminal of the resistor, the high AC impedance of the upper / lower half of the circuit and the high inductive reactance of the common-mode inductor T1 form a double block, preventing it from being converted into a differential-mode signal;

[0039] DC and low-frequency transmission: The feed current (DC) is transmitted through the low DC impedance path of the upper / lower half circuit; the low-frequency ringing signal (20Hz-50Hz) is transmitted through the low-frequency compatibility characteristics of the upper / lower half circuit and the coupling effect of the intermediate circuit.

[0040] Differential mode audio transmission: The audio signal (differential mode) is transmitted between the TIP and the RING resistor through the common mode inductor T1 (low differential mode impedance) and the DC blocking capacitors C2 and C3 (high frequency compatible), with an attenuation of <0.5dB.

[0041] It will be apparent to those skilled in the art that this invention is not limited to the details of the exemplary embodiments described above, and that it can be implemented in other specific forms without departing from the spirit or essential characteristics of this invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of this invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within this invention.

[0042] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This way of describing the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment have been appropriately combined to form other embodiments that are easy for those skilled in the art to understand.

Claims

1. A common-mode rejection circuit for telephone lines, characterized in that, It includes the upper circuit, the lower circuit, and the intermediate coupling circuit; The upper part of the circuit includes transistor Q1, resistor R1, resistor R2, resistor R3, capacitor C1, lines L1 and L4, and rectifier bridge D1; resistor R2 is connected in parallel with capacitor C1 and then in series with resistor R1 to form the bias circuit of transistor Q1. The collector of transistor Q1 is connected to line L4 through resistor R3. Rectifier bridge D1 is connected between TIP_A and TIP_B terminals to adapt the polarity of the TIP terminals. The lower half of the circuit includes transistor Q2, resistor R4, resistor R5, resistor R6, capacitor C4, lines L2 and L3, and rectifier bridge D2; resistor R5 is connected in parallel with capacitor C4 and then in series with resistor R4 to form the bias circuit of transistor Q2. The collector of transistor Q2 is connected to line L3 through resistor R6. Rectifier bridge D2 is connected between resistor RING_A and resistor RING_B to adapt the polarity of resistor RING. The intermediate coupling circuit includes a common-mode line T1 and DC blocking capacitors C2 and C3. The input terminal of the common-mode line T1 is connected to L4 of the upper half circuit and L3 of the lower half circuit, respectively, and the output terminal is connected to TIP_B and resistor RING_B through DC blocking capacitors C2 and C3, respectively.

2. The circuit according to claim 1, characterized in that, In the upper circuit, the resistance of resistor R3 is less than that of resistors R1 and R2, the resistances of resistors R1 and R2 are on the same order of magnitude, and the capacitance of capacitor C1 is ≥1μF; in the lower circuit, the resistance of resistor R6 is less than that of resistors R4 and R5, the resistances of resistors R4 and R5 are on the same order of magnitude, and the capacitance of capacitor C4 is ≥1μF.

3. The circuit according to claim 1, characterized in that, The transistor Q1 is an NPN transistor.

4. The circuit according to claim 1, characterized in that, The transistor Q2 is an NPN transistor.

5. The circuit according to claim 1, characterized in that, The transistors Q1 and Q2 are low-frequency, low-power transistors with a withstand voltage ≥25V and a gain β=50-100.

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