JPH073707Y2 - External trigger detection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to an external trigger detection circuit, and more particularly to an external trigger detection circuit that detects an input of various kinds of external trigger signals and triggers the detection.

[Conventional technology]

For example, in the case of an in-car audio device, when a car phone is called, a mute control is automatically performed to facilitate the call, or a buzzer is issued to alert the user that the call is coming. is there.

Specifically, when a call is made to a car phone, an external trigger signal is output from the car phone body.

This external trigger signal is input to the external trigger input terminal of the vehicle audio device via the external trigger signal line.

The external trigger input terminal is connected to the trigger terminal of the microcomputer as a control circuit via a buffer provided as necessary, and the microcomputer, when a predetermined external trigger signal is input to the external trigger input terminal, It outputs a mute control signal to temporarily stop speaker output, or outputs a warning control signal to a buzzer circuit to generate a buzzer sound.

At this time, the microcomputer receives active "H" or active "L" as an external trigger signal.

[Problems to be solved by the device]

However, in such a conventional technique, if the microcomputer is the active "H", only the active "H",
Also, since only one type of external trigger signal is accepted, such as only active "L" if active "L",
There is a problem that the type of external device that can be connected to the external trigger input terminal of the vehicle audio device is restricted.

In view of the above-mentioned problems of the prior art, the present invention has an object to provide an external trigger detection circuit that can reduce restrictions on external devices that can be connected to an external trigger input terminal.

Another object of the present invention is to obtain an external trigger detection circuit that can trigger without error even when signals of a plurality of frequencies are input.

[Means for Solving the Problems]

The external trigger detection circuit of the present invention inputs an external trigger input terminal for balanced input of an external trigger signal, a first input signal and a second input signal input to the external trigger input terminal via capacitors, respectively, and outputs a differential signal. It is characterized by including a differential amplifier circuit for amplifying and a rectifier circuit for rectifying the output of the differential amplifier circuit and converting it into a DC component.

Another external trigger detection circuit of this invention is characterized in that the capacitor is replaced with BPF.

〔Example〕

 One embodiment of the present invention will be described with reference to FIG.

FIG. 1 is a circuit diagram showing a configuration of an external trigger detection circuit of an in-vehicle audio device according to the present invention.

First on-board audio device 30 as an external trigger input terminal
An input terminal A1 and a second input terminal A2 are provided, and the first input terminal A1 and the second input terminal A2 are connected to the external trigger signal line from an automobile telephone 40 as an example of an external device via an external trigger signal line. Is input in balance.

The first input terminal A1 and the second input terminal A2 are connected to the differential amplifier circuit 14 via DC cut capacitors C1 and C2 and input buffers 10 and 12, respectively.

The differential amplifier circuit 14 has a differential amplifier 16, the non-inverting input terminal (+) of this differential amplifier 16 is connected to the input buffer 10 via the resistor R1, and the inverting input terminal (−) is Resistance R2
Is connected to the input buffer 12 via.

The signal reference voltage V _c is applied to the non-inverting input terminal (+) via the resistor R3.

The output terminal of the differential amplifier 16 is connected to the inverting input terminal (-) via the resistor R4.

The resistors R1 to R4 have the same resistance value in this embodiment.

With the differential amplifier circuit 14 configured in this way, the difference between the outputs of the input buffers 10 and 12 is obtained, and the AC signal component corresponding to the difference between the outputs of the input buffers 10 and 12 is superimposed on the signal reference voltage V _c . Output in the form.

An amplifier 18 is further connected to the output side of the differential amplifier circuit 14, and is amplified to the saturation region for amplitude control.

Here, the signal reference voltage V _c is set to a half voltage of the differential amplifier 16 and the amplifier 18 when, for example, a single power source is used.

The output side of the differential amplifier circuit 14 is a capacitor C3 for DC cut.
Is connected to the rectifier circuit 20 via the, and the level of the AC signal component is converted into the DC component.

An inverter 22 is connected to the output side of the rectifier circuit 20, and the output of the rectifier circuit 20 is inverted and input to the trigger input terminal of the microcomputer 24 as a trigger signal.

When the active "L" is input to the trigger input terminal, the microcomputer 24 performs a predetermined mute control to stop the speaker output.

Next, the operation of this embodiment will be described with reference to the waveform diagrams of FIGS.

First, the external trigger signal output when a call is received from the car telephone 40 is an unbalanced ringing tone signal as shown in FIGS. 2 (1) and 2 (2), and is constant at the first input terminal A1. The sine wave ringing tone signal as an external trigger signal component on the positive DC voltage of is input to the second input terminal A2
The case where only a certain positive DC voltage is input to will be described.

The AC component of the first input signal input to the first input terminal A1 is amplified by the input buffer 10 after the DC component is cut by the capacitor C1.

The output of the input buffer 12 is 0V because the direct current component of the second input signal input to the second input terminal A2 is cut by the capacitor C2.

The difference between the outputs of the input buffers 10 and 12 is obtained by the differential amplifier circuit 14, and is output as a sine wave signal (the phase of the sine wave signal is the same as that of the first input signal) centered on the signal reference voltage V _c. (See FIG. 2 (3)).

At this time, noise generated by the car phone or the car phone
Out of the radiation noise incident from the outside on the external trigger signal line connecting the 40 and the on-vehicle audio equipment, the in-phase noise components on the first input signal and the second input signal are canceled out, so that malfunction due to noise is reduced.

The output of the differential amplifier circuit 14 is amplified by the amplifier 18 and output as a signal whose amplitude is limited between the saturation region and 0 V centered on V _c (see FIG. 2 (4)).

The DC component of the amplitude limiting signal is cut by the capacitor C3, and then converted into a DC level according to the level of the AC signal component by the rectifier circuit 20.

Therefore, the output of the rectifier circuit 20 is 0V when the ringing tone signal is not yet input, but when the ringing tone signal is input,
A predetermined positive level DC voltage is output (see FIG. 2 (5)).

Since the output of the rectifier circuit 20 is input to the inverter 22, the output of the inverter 22 outputs "H" level when the output of the rectifier circuit 20 is 0V, and conversely, when the rectifier circuit 20 outputs a predetermined DC level. The "L" level is output (see FIG. 2 (6)).

The "L" level input from the inverter 22 triggers the microcomputer 24 to output a mute control signal.

Next, the external trigger signal output when a call is received from the car telephone 40 is an unbalanced ringing tone signal as shown in (1) and (2) of FIG. 3, and the first input terminal A1
A case where 0 V is input and a signal in which a square-tone ringing tone signal as an external trigger signal component is added to a constant positive DC voltage is input to the second input terminal A2 will be described.

The output of the input buffer 10 is 0V, and the output of the input buffer 12 is only the square wave signal component.

At this time, the signal output from the differential amplifier circuit 14 becomes a square wave signal (the phase of the square wave signal is opposite to that of the second input signal) centered on the signal reference voltage V _c ((3) in FIG. 3). (See Fig. 3 (4))
reference).

Therefore, the output of the rectifier circuit 20 is 0 V when the ringing tone signal is not yet input, and when the ringing tone signal is input, a predetermined positive level DC voltage is output (see FIG. 3 (5)). ).

As a result, a trigger signal of active "L" is input to the microcomputer 24 when a call is received, as in the case of FIG. 2 (see FIG. 3 (6)), and the microcomputer 24 Execute mute control.

On the other hand, the external trigger signal output when a call is received from the car telephone 40 is a balanced ringing tone signal as shown in FIGS. 4 (1) and (2), and the first input terminal A1
Is input with a sine wave ringing tone signal that rides on a certain positive DC voltage, and a sine wave ringing tone signal that is riding on a certain positive DC voltage and has a phase difference of 180 degrees is input to the second input terminal A2. The case will be described.

Both the first input signal and the second input signal input to the first input terminal A1 and the second input terminal A2 have their DC components cut by the capacitors C1 and C2, and the AC components are amplified by the input buffers 10 and 12. It

A difference between the outputs of the input buffers 10 and 12 is obtained by the differential amplifier circuit 14, and a sine wave signal whose phase is centered around the signal reference voltage V _c and which is twice the AC component of the first input signal (the phase is The same as one input signal) is output (see FIG. 4 (3)).

When this signal is amplified by the amplifier 18, it becomes an amplitude limiting signal centered on the signal reference voltage V _c (see FIG. 4 (4)).

Therefore, as in the case of FIG. 2 and FIG. 3, the output of the rectifier circuit 20 is 0 V when the ringing tone signal is not yet input, but when the ringing tone signal is input, it has a predetermined positive level. It becomes a DC voltage (see FIG. 4 (5)).

Since the output of the rectifier circuit 20 is input to the inverter 22, the output of the inverter 22 outputs "H" level when the output of the rectifier circuit 20 is 0V, and conversely, when the rectifier circuit 20 outputs a predetermined DC level. The "L" level is output (see FIG. 4 (6)).

The "L" level input of the inverter 22 triggers the microcomputer 24 to output a mute control signal.

In addition, the external trigger signal output when a call is received from the car telephone 40 is a special signal as shown in FIGS. 5 (1) and 5 (2), and a constant positive DC voltage is applied to the first input terminal A1. When a triangular wave signal as an external trigger signal component on the voltage is input and a sine wave signal as an external trigger signal component whose amplitude gradually increases is input to the second input terminal as a positive plus DC voltage. Will be explained.

Both the first input signal and the second input signal input to the first input terminal A1 and the second input terminal A2 have their DC components cut by the capacitors C1 and C2, and the AC components are amplified by the input buffers 10 and 12. It

A difference between the outputs of the input buffers 10 and 12 is obtained by the differential amplifier circuit 14, and an irregular AC signal centered on the signal reference voltage V _c is output (see FIG. 5 (3)).

When this signal is amplified by the amplifier 18, it becomes an irregular amplitude limiting signal centered on the signal reference voltage V _c (Fig. 5).
(See (4)).

However, when this irregular amplitude limiting signal is rectified by the rectifying circuit 20, it is 0 V before the external trigger signal is input,
When an external trigger signal is input, a predetermined positive level DC voltage is output as in FIGS. 2 to 4 (see FIG. 5 (5)), and the inverter 22 outputs "L" level (see FIG. 5 (5)). See FIG. 5 (6).

Therefore, the microcomputer 24 can be triggered in the same manner as described above, and the mute control is performed.

According to this embodiment, the first input terminal A1 and the second input terminal A2
Balance the external trigger signal with and input capacitors C1 and C2.
After the DC component is cut with, differential amplification is performed with the differential amplifier circuit 14, the amplitude is further limited with the amplifier 18, and then the AC component is rectified with the rectifier circuit 20 to detect the external trigger signal and input to the inverter 22. By converting the trigger signal into a signal that can be input by the microcomputer 24, the presence or absence of DC bias in the external trigger signal, unbalanced or balanced signal input format, and external trigger such as sine wave or triangular wave An external trigger signal can be detected regardless of the type of signal component, and the microcomputer 24 can be triggered. There are less restrictions on the devices that can be connected to.

Also, of the noise generated on the car telephone 40 side and the radiation noise incident from the outside on the external trigger signal line that connects the car telephone and the car audio device, the common mode component is removed by the differential amplifier circuit 14, so malfunction Hard to do.

Although the amplifier 18 is provided on the output side of the differential amplifier circuit 14 in the above-described embodiment, it is not particularly necessary when the input level of the external trigger signal is high, and the differential amplifier circuit 14 has a gain. It can be substituted.

Further, the case has been described in which the first input signal and the second input signal input to the first input terminal A1 and the second input terminal A2 all change at a positive level, but they change at a negative level.
It may be a signal that changes over both positive and negative polarities.

When the microcomputer 24 receives active "H" as a trigger input and the positive level DC voltage output from the rectifier circuit 20 satisfies the input rating of the microcomputer 4, the inverter 22 may not be provided.

In addition, connect capacitors C1 and C2 to B
Instead of PF, only the signal of a certain frequency component is extracted as an external trigger signal and input to the differential amplifier circuit 14, so that signals of various frequencies can be output from the device connected to the external trigger input terminal. When the signal is output to, the trigger can be triggered without error only when a signal of a specific frequency such as a ringing tone signal is received.

Further, when the trigger is applied, the microcomputer may perform other control such as issuing control for the buzzer.

Further, the external trigger detection circuit may be mounted on a device other than the vehicle audio device.

[Effect of device]

According to the external trigger detection circuit of the present invention, the external trigger input terminal for balanced input of the external trigger signal, the first input signal and the second input signal input to the external trigger input terminal are respectively input via the capacitors, By providing a differential amplifier circuit that differentially amplifies and a rectifier circuit that rectifies the output of the differential amplifier circuit and converts it into a DC component, presence or absence of DC bias of an external trigger signal, unbalanced type, and balanced type Regardless of the signal input format of, it is possible to detect various external trigger signal components and trigger a predetermined circuit.
There are less restrictions on the devices that can be connected to the external trigger input terminal.

Furthermore, since the in-phase noise component is removed by the differential amplifier circuit, an external trigger detection operation resistant to noise can be performed.

Also, by changing the capacitor to BPF, even if multiple signals with different frequency components are output from the external device connected to the external trigger input terminal, the trigger can be applied without error only when a specific signal component is input. be able to.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an external trigger detection circuit according to an embodiment of the present invention, and FIGS. 2 to 5 are diagrams when different kinds of external trigger signals are input to the external trigger detection circuit of FIG. 1, respectively. 6 is a waveform diagram showing the operation of FIG. Explanation of main symbols 14: Differential amplifier circuit, 20: Rectifier circuit, C1, C2: Capacitor.

Claims (2)

[Scope of utility model registration request] 1. An external trigger input terminal for balanced input of an external trigger signal, and a differential for differentially amplifying by inputting a first input signal and a second input signal input to the external trigger input terminal through capacitors respectively. An external trigger detection circuit, comprising: an amplifier circuit; and a rectifier circuit that rectifies the output of the differential amplifier circuit and converts it into a DC component. 2. The external trigger detection circuit according to claim 1, wherein the capacitor is replaced with BPF.