Interphone K head audio differential output circuit

Abstract

The invention discloses an interphone K head audio differential output circuit, and relates to the technical field of communication. The circuit comprises an interface module composed of 3.5 mm and 2.5 mm earphone interfaces, a partial pressure detection module composed of resistors R7, R6, R8, R4 and R1, and a switching control module composed of an MOS tube Q1, triodes Q2 and Q3 and a bias resistor thereof. By detecting AUX voltage change caused by external equipment (an earphone or a frequency writing line), a GEN control signal is output, and working modes of the circuit are automatically switched: in an earphone mode, Q2 and Q3 are cut off, Q1 is switched on, differential audio output of SPK + and SPK-is realized, and sound quality and anti-interference performance are improved; in a frequency writing mode, the Q2 and the Q3 are conducted, the Q1 is cut off, the SPK-is used as a ground wire, and the normal frequency writing function is ensured. On the basis that all original functions of the K head are reserved, differential driving of audio output is achieved, and the circuit has the advantages of being high in common-mode rejection ratio, intelligent in switching, low in cost and good in compatibility.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of communication technology, in particular to a circuit for differential output of K-head audio of intercom. BACKGROUND

[0002] As an important instant communication tool, intercom is widely used in professional dispatch, engineering construction, outdoor activities and other scenarios; in order to meet different use requirements, intercom is usually equipped with a headset interface for private listening or using a frequency line for parameter configuration; among many interface standards, K-head interface originated from Kenwood has become one of the market mainstream due to its comprehensive functions.

[0003] The standard K-head headset interface is composed of a 3.5mm three-section plug and a 2.5mm three-section plug, which defines a total of six connection points to support PTT (push-to-talk), MIC (microphone input), SPK+ (audio signal positive), SPK- (audio signal negative) and ground functions of intercom.

[0004] At present, most intercoms on the market using K-head interface have a significant defect in audio output: in order to be compatible with PTT and MIC functions, the negative pole (SPK-) of the audio signal is usually short-circuited with the common ground or equivalent to the ground in circuit design; this makes the audio output mode essentially "single-ended output"; in this mode, the positive pole (SPK+) of the audio signal carries the signal, while SPK- acts as a common reference ground; the disadvantage of this approach is that when the transmission line is long or in a complex electromagnetic environment, external interference will be equally coupled to the signal line and the ground. Since the receiver (such as a headset) interprets the signal by referencing the ground, these common-mode disturbances will be converted into differential-mode noise, resulting in a decrease in the signal-to-noise ratio of the audio output, a deterioration in sound quality, and the presence of noticeable background noise or distortion.

[0005] Therefore, there is an urgent need in the art for an improved circuit for K-head interface that can upgrade the audio output mode to differential output with stronger anti-interference capability while maintaining the integrity of the original functions such as PTT, MIC and frequency writing. SUMMARY

[0006] The purpose of the present application is to overcome the shortcomings of the prior art and provide a circuit for differential output of K-head audio of intercom. The circuit can intelligently identify the type of external device (headset or frequency writing line) and automatically switch the working mode of the circuit: when using a headset, it realizes double-ended differential audio output of SPK+ and SPK- to improve sound quality and anti-interference; when using a frequency writing line, it restores the traditional grounding mode to ensure the normal operation of the frequency writing function.

[0007] In order to achieve the above purpose, the present application adopts the following technical solution: a circuit for differential output of K-head audio of intercom, comprising: One 3.5mm triple headphone jack and one 2.5mm triple headphone jack for connecting external headphones and programming cables; The voltage divider resistor module includes resistors R7, R6, R8, R4 and R1, which are connected in series to provide different voltages to the AUX detection pin; The bias resistor module, including resistors R3 and R2, is used to provide the base bias voltage for transistor Q3; The source of the MOSFET Q1 is connected to the audio output signal SPK-, and the drain is connected to the SPK- pin of the headphone jack. It is used to control the connection between the audio output signal and the headphone output port. Transistor Q2, with its collector connected to ground and its emitter connected to the ground pin of the headphone jack, is used to use SPK- as ground in write mode; Transistor Q3 has its collector connected to the gate of MOSFET Q1, its emitter grounded, and its base connected to the bias resistor module, which is used to control the conduction and cutoff of MOSFET Q1. The circuit is configured as follows: When headphones are used, the AUX detects a voltage change, sets the GEN signal to a low level, turns off transistors Q2 and Q3, and turns on MOSFET Q1, thereby connecting the audio output SPK- to the headphone jack, realizing dual-ended differential audio output of SPK+ and SPK-. When the programming cable is used, the AUX detects a voltage change, sets the GEN signal to a high level, turns on transistor Q2 to ground, which serves as the ground line for the programming cable. At the same time, transistor Q3 turns on and MOSFET Q1 turns off, disconnecting the audio output SPK- from the headphone jack.

[0008] Preferably, in the voltage divider resistor module, resistors R7, R6, R8, R4 and R1 are connected in series, wherein R7 is connected to the power supply voltage, R1 is connected to ground, and the AUX detection pin is connected to the middle node of the voltage divider resistor to detect the insertion status of the external device.

[0009] Preferably, in the bias resistor module, resistor R3 is connected to the base of transistor Q3, and resistor R2 is connected between the base and ground to set the base bias current of transistor Q3.

[0010] Preferably, the MOSFET Q1 is an N-channel MOSFET, and its gate is controlled by the collector of the transistor Q3. When the transistor Q3 is turned on, the MOSFET Q1 is turned off; when the transistor Q3 is turned off, the MOSFET Q1 is turned on.

[0011] Preferably, the triode Q2 is an NPN transistor, and the base thereof receives the GEN signal, and when the GEN is high, the triode Q2 is turned on to ground the SPK- pin of the earphone interface.

[0012] Preferably, the triode Q3 is an NPN transistor, and the base thereof receives the bias voltage through the bias resistor module, and when the GEN is high, the triode Q3 is turned on to pull down the gate voltage of the MOS tube Q1.

[0013] Preferably, the circuit further comprises an AUX detection module connected with the voltage dividing resistor module, for judging the type of the external device according to the voltage change of the voltage dividing resistor module, and outputting a corresponding GEN control signal.

[0014] Preferably, the AUX detection module is integrated in the intercom master control chip, and the voltage value of the voltage dividing resistor module is sampled through an ADC, and whether the earphone is inserted or the write frequency line is inserted is judged according to a preset voltage threshold.

[0015] Preferably, when the circuit is in the audio output mode, the SPK+ and the SPK- output audio signals of opposite phases respectively to form differential output, so as to improve the common mode rejection ratio and the anti-interference ability.

[0016] Preferably, when the circuit is in the write frequency mode, the triode Q2 is turned on to provide a ground path, and at the same time, the MOS tube Q1 is turned off to prevent the audio output signal SPK- from being short-circuited with the ground, so as to ensure the normal operation of the write frequency.

[0017] Compared with the prior art, the present application has the following beneficial effects: 1. High sound quality and high anti-interference: by changing the single-ended audio output to a true differential output, the high common mode rejection ratio characteristic of differential transmission is fully utilized, and the common mode noise introduced in the transmission process is greatly suppressed, so that the audio output is clearer and has higher fidelity.

[0018] 2. Intelligent function switching: the circuit can automatically identify the external device and seamlessly switch between differential audio output and traditional ground mode, without any manual operation by the user, and the experience is smooth.

[0019] 3. Good backward compatibility: while realizing the differential output to improve the performance, all the functions of the K-head interface are completely retained, including PTT, MIC and write frequency, and the present accessory is completely compatible.

[0020] 4. Low cost and easy to implement: the components used are common resistors, triodes and MOS tubes, which are very low in cost; the circuit structure is simple, and the core audio architecture of the intercom mainboard does not need to be changed, so it is easy to integrate into the existing products, and has high practical value and commercial promotion value. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The circuit schematic diagram of the embodiment of the present application.

[0022] In the figure: J1 and J2 represent a 2.5mm three-section earphone interface and a 3.5mm three-section earphone interface respectively; AUX is a device detection point; GEN is a mode control signal from a master control; SPK+ and SPK- are differential signals from an audio power amplifier; Q1 is a MOS tube, and Q2 and Q3 are NPN type triodes; R1-R4 and R6-R8 are resistors. DETAILED DESCRIPTION

[0023] In order to further explain the technical solutions of the present application, the following will be described in detail through specific embodiments.

[0024] Please refer to Figure 1 The present application provides a circuit for differential output of a speakerphone K head audio, which is characterized in that it comprises an interface module, a detection module and a switching control module.

[0025] The interface module comprises a 3.5mm three-section earphone interface and a 2.5mm three-section earphone interface, which are used for external earphone or frequency writing line.

[0026] The detection module comprises a voltage division circuit composed of resistors R7, R6, R8, R4 and R1; the circuit is connected between a power supply voltage and ground, and its AUX detection point is led out from a voltage division node and connected to an ADC (analog-to-digital converter) input pin of a speakerphone master control chip; when a device with different impedance characteristics (such as an earphone or a frequency writing line) is connected to the interface, the total load of the voltage division circuit will be changed, thereby causing a significant change in the voltage of the AUX detection point; the master control chip samples the voltage and compares it with a preset threshold value, so as to determine the type of the currently inserted device and correspondingly output a GEN control signal (high level or low level).

[0027] The switching control module is the core for realizing function switching, which comprises: A bias resistor circuit composed of resistors R2 and R3, which is used for providing a stable base bias for the triode Q3.

[0028] A ground wire path switch: an NPN type triode Q2 is used; its collector is connected to a system ground, and its emitter is connected to the SPK- pin of the earphone interface; its base is controlled by the GEN signal; when the GEN is high, the triode Q2 is turned on, and the SPK- pin is forced to be pulled down to the ground potential, thereby serving as the ground wire of the frequency writing line.

[0029] Audio path switch: an N-channel MOS tube Q1 and an NPN transistor Q3 are adopted; the source of the MOS tube Q1 is connected to the SPK- signal of the intercom audio power amplifier output, and the drain is connected to the SPK- pin of the earphone interface; the collector of the transistor Q3 is connected to the gate of the MOS tube Q1, and the emitter is grounded; the base thereof is controlled by the biasing resistor and the GEN signal.

[0030] The working principle of the circuit for the differential output of the intercom K head audio is as follows: 1. Earphone mode: When the earphone is inserted, the AUX voltage change of the detection module is recognized by the master control chip, and the GEN signal is set to low level; The GEN is low level, so that the transistor Q2 is cut off, and the direct connection between the SPK- pin and the system ground is cut off; At the same time, the GEN is low level, so that the transistor Q3 is also in the cut-off state; at this time, the gate of the MOS tube Q1 is pulled up by the pull-up resistor, so that the MOS tube Q1 is turned on; Therefore, the original differential signal (SPK+ and SPK-) of the intercom audio power amplifier output is completely and mutually short-circuited to the earphone, and the earphone receives a pair of differential signals with opposite phases and equal amplitudes, which has strong suppression ability to external common-mode interference, thereby significantly improving the sound quality.

[0031] 2. Write frequency mode: When the write frequency line is inserted, the AUX voltage change of the detection module is recognized by the master control chip, and the GEN signal is set to high level; The GEN is high level, so that the transistor Q2 is saturated and conducts, and the SPK- pin of the earphone interface is firmly grounded, providing the necessary ground loop for the write frequency device; At the same time, the GEN is high level, so that the transistor Q3 is saturated and conducts, and its collector (i.e. the gate of the MOS tube Q1) is pulled down to the ground potential, resulting in the complete cut-off of the MOS tube Q1; In this way, the audio output signal SPK- is completely disconnected from the earphone interface, avoiding the short circuit of the audio circuit to the ground during the write frequency process, thereby ensuring the stability and reliability of the write frequency operation.

[0032] The specific connection of the circuit of the embodiment is as follows: The voltage division detection network is composed of resistors R7 (10kΩ), R6 (10kΩ), R8 (10kΩ), R4 (10kΩ) and R1 (10kΩ) connected in series, one end of which is connected to a 3.7V power supply, and the other end is grounded; the AUX detection point is taken from the node between R6 and R8, and is connected to the ADC pin of the master control chip.

[0033] Control part: GEN signal comes from master GPIO; when in earphone mode, GEN outputs 0V low level; when in write frequency mode, GEN outputs 3.7V high level.

[0034] The base of triode Q2 receives GEN signal through a 1kΩ current limiting resistor; when it is turned on, the SPK- pin of the interface is connected to the ground through a saturation voltage drop of about 0.2V.

[0035] The base of triode Q3 is divided by bias resistors R3 (10kΩ) and R2 (10kΩ), also controlled by GEN signal; when GEN is high level, triode Q3 is turned on.

[0036] MOS tube Q1 selects a small signal N-channel MOSFET, such as 2N7002; its gate is directly connected to the collector of triode Q3, when triode Q3 is off, the gate is pulled up to 3.7V, MOS tube Q1 is turned on, its on-resistance is very small, the audio signal attenuation can be ignored; when triode Q3 is turned on, the gate of MOS tube 1 is low, MOS tube Q1 is reliably cut off.

[0037] The specific working process is as follows: 1. The user inserts the earphone, the master recognizes the earphone insertion through AUX voltage, and sets GEN to low level.

[0038] 2. Triode Q2 and triode Q3 are cut off because the base is low.

[0039] 3. The gate of MOS tube Q1 is high, MOS tube Q1 is turned on; the differential signal of SPK+ and SPK- of audio power amplifier output is sent to the earphone through the corresponding pins of interface J1 / J2 without loss.

[0040] 4. The user unplugs the earphone and plugs in the write frequency line; the master recognizes the write frequency line insertion through AUX voltage, and sets GEN to high level.

[0041] 5. Triode Q2 and triode Q3 are saturated and turned on because the base is high.

[0042] 6. Triode Q2 is turned on to provide a ground loop for the write frequency line.

[0043] 7. Triode Q3 is turned on to pull down the gate of MOS tube Q1 to ground, MOS tube Q1 is cut off, cutting off the connection between audio SPK- signal and the interface, preventing it from being short-circuited to ground, and ensuring normal write frequency communication.

[0044] The above merely describes the preferred examples of the present application and is not intended to limit the present application. Although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art will appreciate that modifications can be made to the foregoing embodiments, or some of the technical features thereof can be equivalently replaced, without departing from the spirit and principle of the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A circuit for a talkback K-head audio differential output, characterized by, The circuit comprises: a 3.5mm 3-pin earphone interface and a 2.5mm 3-pin earphone interface for external earphone and write frequency line; a voltage dividing resistor module comprising resistors R7, R6, R8, R4 and R1, which are connected in series to provide different voltages for the AUX detection pin; a bias resistor module comprising resistors R3 and R2 for providing a base bias voltage for the transistor Q3; a MOS tube Q1, the source of which is connected to the audio output signal SPK-, and the drain of which is connected to the SPK- pin of the earphone interface, for controlling the connection between the audio output signal and the earphone output port; a transistor Q2, the collector of which is connected to the ground, and the emitter of which is connected to the ground pin of the earphone interface, for using SPK- as ground in write frequency mode; a transistor Q3, the collector of which is connected to the gate of the MOS tube Q1, the emitter of which is grounded, and the base of which is connected to the bias resistor module, for controlling the conduction and cutoff of the MOS tube Q1; wherein the circuit is configured to: when using earphones, the AUX detects a voltage change, the GEN signal is set to low, the transistors Q2 and Q3 are cut off, and the MOS tube Q1 is turned on, thereby connecting the audio output SPK- to the earphone interface and realizing double-ended differential audio output of SPK+ and SPK-; when using a write frequency line, the AUX detects a voltage change, the GEN signal is set to high, the transistor Q2 is turned on to ground as the ground of the write frequency line, and the transistor Q3 is turned on, the MOS tube Q1 is cut off, and the audio output SPK- is disconnected from the earphone interface.

2. The circuit for the audio differential output of a K-head intercom according to claim 1, characterized in that: The resistors R7, R6, R8, R4 and R1 in the voltage dividing resistor module are connected in series, with R7 connected to the power supply voltage and R1 connected to the ground, and the AUX detection pin connected to the middle node of the voltage dividing resistor for detecting the insertion state of the external device.

3. The circuit for the audio differential output of a K-head intercom according to claim 1, characterized in that: The resistor R3 in the bias resistor module is connected to the base of the transistor Q3, and the resistor R2 is connected between the base and the ground, for setting the base bias current of the transistor Q3.

4. The circuit for the audio differential output of a K-head intercom according to claim 1, characterized in that: The MOS tube Q1 is an N-channel MOSFET, and its gate is controlled by the collector of the transistor Q3, which is cut off when the transistor Q3 is turned on, and is turned on when the transistor Q3 is cut off.

5. The circuit for the audio differential output of a K-head intercom according to claim 1, characterized in that: The transistor Q2 is an NPN transistor, and its base receives the GEN signal, which is turned on when the GEN is high, grounding the SPK- pin of the earphone interface.

6. The circuit for the audio differential output of a K-head intercom according to claim 1, characterized in that: The transistor Q3 is an NPN transistor, and its base receives a bias voltage through the bias resistor module, which is turned on when the GEN is high, pulling down the gate voltage of the MOS tube Q1.

7. The circuit for the audio differential output of a K-head intercom according to claim 1, characterized in that: The circuit further comprises an AUX detection module connected to the voltage dividing resistor module, for judging the type of external device according to the voltage change of the voltage dividing resistor module and outputting the corresponding GEN control signal.

8. The circuit for the audio differential output of a K-head intercom according to claim 7, characterized in that: The AUX detection module is integrated in the intercom main control chip, samples the voltage value of the voltage dividing resistor module through ADC, and judges whether the earphone is inserted or the write frequency line is inserted according to the preset voltage threshold.

9. The circuit for the audio differential output of a K-head intercom according to claim 1, characterized in that: When the circuit is in audio output mode, SPK+ and SPK- output audio signals with opposite phases respectively, forming a differential output to improve common-mode rejection ratio and anti-interference capability.

10. The circuit for the audio differential output of a K-head intercom according to claim 1, characterized in that: When the circuit is in write frequency mode, triode Q2 is turned on to provide a ground path, while MOS tube Q1 is turned off to prevent audio output signal SPK- from being short-circuited to ground, ensuring normal write frequency operation.

Images