DE69331685T2 - Method and device for testing connections between amplifier and loudspeaker - Google Patents

Description

The present invention relates generally to a communication device and, more particularly, to DSP communication devices with diagnostic capabilities.

In the manufacture of communication systems such as radios and in the manufacture of vehicles in which radios are installed, it is common practice to test the communication device before delivery to the customer. Given the large number of components in such a system, and given the distribution of these components throughout the vehicle in which they are installed, it is extremely difficult, if not impossible, to test point by point all the connection points between the components in the system. In addition, it is easy to see that a visual inspection is difficult to detect electrical connection problems which could interfere with the operation of the system or create a risk of damage to these improperly connected components. components. Therefore, diagnostic devices have been developed to check the operation of the communication systems.

One previously known form of apparatus for testing communications systems includes a separate device designed to interact with the various parts of the system. Radio receivers, amplifiers, demodulators and the like can, for example, be tested when they interact with the circuits of the test device. The test circuit can also provide signals that are passed on to other parts of the system to test the function of certain controls or circuits such as sound controls, loudspeakers or graphic equalizers. However, such systems require the connection of the test device to parts of the radio device under test, which involves unplugging parts of the system so that the test device can be connected instead. Preparation for testing the radio system with such previously known test devices can therefore be laborious, difficult and time-consuming.

Patent disclosure DD-A-267 616 describes a measuring method and measuring device for a communication system that includes a processor connected to a D/A converter via an I/O coupling. The D/A converter is connected to a sine wave generator that feeds a loudspeaker. The loudspeaker is acoustically connected to a receiver that feeds an A/D converter. The A/D converter is connected to send a digital signal back to the processor through the I/O coupling. In this way, the processor can set the sine wave generator to generate a test signal to be received by the receiver. The level of the test signal returned via the receiver can be monitored to ensure correct connection of the loudspeaker.

It is also known to provide the communication device with a self-test circuit. Such a circuit, in particular Circuits for use in analyzing analog signals can be quite complex and significantly increase the manufacturing costs of the communication device. In addition, such a device is often limited to testing specific signal functions and does not allow changes to individual parameters in a range in which the device is intended to work correctly. In particular, such changes may have to be made manually and therefore require experience and skill in order to be able to operate the test device properly.

In addition, while parts of the communication system, such as the radio receiver, can be tested for operability at the factory before they are installed in the vehicle, it may also be necessary to test whether the communication system is working after it has been installed in the vehicle. However, the known test equipment does not allow for testing whether the system as a whole has been properly installed in a vehicle or other environment. In particular, the installation of a system often requires distributed loudspeakers that must be connected to the amplifier. With recent improvements in audio reproduction systems, in which concert hall emulation and other features have become available through digital signal processing, the operation of the loudspeakers within the system has become even more important than in previously known mono or stereo systems, since each loudspeaker makes a special, defined contribution to the audio output and is not merely a redundant audio source. Consequently, the connection between each speaker and the amplifier is important in system operation, but is extremely difficult to monitor in the mounted vehicle.

The present invention addresses the above disadvantages by providing a communication system with self-diagnostic circuits to determine the status of the amplifier-speaker connection. Generally, the system provides an input to an amplifier and the output of the amplifier is tested to determine the status of the amplifier output without requiring disassembly or connection of a test device to the already installed communication system. In addition, the system performs a diagnostic routine using the existing control mechanism of the communication system and thus does not require a significant number of additional components to be installed in the communication system.

According to the present invention, there is provided a method for diagnosing an electrical connection between a power amplifier and a loudspeaker in a communication system, comprising:

Initiating a diagnostic routine by selecting a specified input on a control unit;

Generating a predetermined tone signal in response to the selected input;

Applying said audio signal to said amplifier;

Detecting the output of said amplifier;

Changing the level of said audio signal;

Monitoring the level of the audio signal at which clipping occurs at an amplifier output; and

Indicates whether clipping occurs within a specified range of audio signal levels.

Further according to the present invention, there is provided a DSP communication system with a diagnostic circuit for diagnosing an electrical connection between a power amplifier and a loudspeaker in the communication system, which includes:

an operating unit with means for initiating a diagnostic routine by selecting a specified input on the operating unit;

a DSP processor unit having programmable means for generating a predetermined test signal in response to said predetermined input, and for controlling the magnitude of the test signal; and

a D/A converter for applying the test signal to the power amplifier;

marked by

a detector connected to an output of the amplifier for determining a threshold value above which the amplifier generates a clipped output signal;

a monitoring circuit for determining the level of the test signal level at the threshold level at which the clipping thus detected occurs; and

Means for indicating whether the amplifier is properly connected to a loudspeaker by comparing the signal level sensed at the occurrence of clipping with a predetermined range of levels.

In the preferred embodiment, a digital signal processor includes a generator for producing an input signal with a predetermined signal level to the amplifier. A feedback signal preferably identifies the amplitude level of the signal so produced. In addition, a clipping detector reports the occurrence of signal clipping in the amplifier. The clipping detector preferably also includes a feedback loop which identifies the clipped output to a digital signal processing and control device (DSP).

If clipping occurs at an input signal amplitude that is below a predetermined level, the DSP detects a short circuit condition. Likewise, clipping detected at an input voltage amplitude greater than a predetermined level indicates an open circuit condition between the amplifier and the loudspeaker. In each situation, appropriate detection signals can be generated that allow easy detection by the test personnel, e.g. a visual indicator can be switched on on the control panel façade of the radio system, which makes the detected condition recognizable. If clipping occurs within a predetermined range of input voltages delivered to the amplifier, the system is in a proper operating condition, and this too The condition of the circuit can be indicated by appropriate detection signals generated in response to the test.

The diagnostic cycle can be called up by pressing certain buttons, e.g. by a combination of control buttons on the front panel of the DSP radio. The DSP generator preferably produces a generally inaudible tone, i.e. a tone in a frequency range to which the human ear hardly responds, such as 19 kHz, so that the user is not disturbed by this tone during the test. Several loudspeakers can be tested in this way in sequence with the device.

The present invention also provides a method and apparatus for diagnosing radio circuit conditions, such as the electrical connection between an amplifier and a loudspeaker, within the system itself without increasing the package size required for the system. The amplifier-loudspeaker connection is tested by initiating a diagnostic routine at the radio control unit which generates a signal and applies it to the amplifier, then sensing the amplifier response, monitoring the level at which clipping occurs, and indicating whether the level at clipping represents an acceptable performance condition in the connection. The input signal level is automatically varied while the above steps are repeated to determine a clipping threshold which represents the condition of the connection.

The DSP radio system includes a diagnostic trigger which uses the radio function actuator and a programmed processor to generate a test signal which is applied to the amplifier and to detect the amplifier's response to the signal, as well as to monitor the level at which the amplifier output becomes undesirably distorted and to indicate the link condition in response to the relative signal level at which clipping occurs. The DSP radio system with a comparator in the DSP chip is set to compare the signal level at the cut-off threshold with a predetermined normal level range between a limit level indicating a short circuit and a limit level indicating an open circuit between the amplifier and the loudspeaker. The DSP radio system is used to test all the loudspeakers in a multi-loudspeaker system in sequence.

The invention will now be explained in more detail by way of example with reference to the accompanying drawings, in which:

Fig. 1: a schematic view of the communication system in which the diagnostic device and the diagnostic method according to the present invention are used;

Fig. 2: an enlarged front elevation view of the control panel front shown in Fig. 1;

Fig. 3: a partially detailed schematic view of a part of the system shown in Fig. 1; and

Fig. 4: a graphical representation of a transfer function of the load impedance to the output voltage, which demonstrates the performance of the inventive diagnostic device.

Referring now to Fig. 1, there is shown a communications system 10 which includes numerous parts generally arranged in a manner particularly suitable for installation in a motor vehicle. In particular, a front control unit 12 is designed to be installed in the dashboard of the motor vehicle, while a control box 14 with an AM/FM radio receiver unit 24 is installed in the trunk of a motor vehicle along with selected accessories such as a CD player 15. The antenna 35 is externally mounted but coupled to the receiver device 24. The number and location of the accessories can be varied as desired without departing from the spirit of the invention. although a cassette player 25 is preferably installed in the front control unit for convenience. The trunk also contains an amplifier 34 which is connected by conductors to a left front speaker 16, a left rear speaker 18, a right front speaker 20 and a right rear speaker 22 which in the preferred embodiment are distributed throughout the passenger compartment of the vehicle for convenience. However, the number and arrangement of the speakers can be changed as desired.

The control box 14 also includes an analog multiplexer 41, e.g. two four-input analog switches for selecting the signals from the receiver 24, the CD player 15 or the cassette tape drive 25 for forwarding to an analog-to-digital (A/D) converter 30. The multiplexer 41 preferably provides a differential input to the A/D converter 30 so that the effects of changing environmental conditions in the vehicle's environment are reduced. The A/D converter 30 is part of the signal processing chipset 26, which has a digital signal processing chip (DSP) 43 (see Fig. 3), a microprocessor chip 27 (see Fig. 1), a digital audio signal processor (DASP) 31 (see Fig. 3) and a digital-to-analog converter chip (D/A) 32 (see Fig. 3).

In a preferred embodiment, a 16-bit two-channel audio converter, e.g. a Philips SAA 7364, can be advantageously connected to the DSP chipset 28. The chipset 28 includes a combination of circuits or chips such as an IC 43, e.g. a TMS 320C25 DSP integrated circuit from Texas Instruments, and an IC chip 31, e.g. a model TMS 57002 from Texas Instruments. The D/A converter includes an 18-bit four-channel D/A converter 32, e.g. a Philips TDA 1314. This converter 32 provides two additional bits for a separate 12 dB improved dynamic range (6 dB per bit), which enables digital attenuation control (so-called fading control) instead of a digitally controlled analog fading circuit in the Connection to the converter 32 so that the amplifier 34 is fed with a signal in which the priority of each channel 17, 19, 21 and 23 can be individually set. The DSP chipset 28 is also coupled to a microprocessor chip 27, e.g. a Motorola HC11, which is designed to provide conventional serial communications, e.g. for communications in accordance with SAE standard J 1850, together with a compatible microprocessor chip 29, e.g. another Motorola HC11.

As generally shown in Fig. 1, the front panel 12 includes control buttons 42-62 accessible to the operator and a display unit 66 for displaying the system conditions set by the control buttons. As particularly shown in Fig. 2, the front panel includes a plurality of control devices such as rotary switches 42, 44 and 46, single-acting push buttons 48, 50, 52, 54, 56 and 58, and double-acting push buttons 60 and 62. A display screen 66 may be provided by an LCD screen or the like, which displays the status of the communication devices and the settings entered by the operator on the front panel 12.

While each control switch may typically have a single function, all of the control buttons may be used in combination with other control buttons to select functions not normally associated with the use of the communication devices. For example, while switch 62 may often be used for the play and rewind functions of a cassette tape recorder, indicated generally at 68, actuation of the dual control buttons 60 and 62 to the right in conjunction with the simultaneous depression of switch 58 may be used in the present invention to initiate a diagnostic program. In particular, it can be readily seen that such multiple actuation of switches constitutes an actuation device which controls the communication system in a manner which is different from the individual actuation of the individual control buttons on the control panel 12. Regardless of the combination of the Control buttons selected to initiate the diagnostic routine, the control signal is supplied via the microprocessor 27 to the digital signal processing microprocessor 28.

Referring to Fig. 3, when the diagnostic invoking switch combination, e.g. 58, 60 and 62, is actuated, the DSP microprocessor 28 is started to produce an audio signal with maximum output power as shown schematically at 70.

In the preferred embodiment, a clipping detection feedback loop 74 is provided which applies a tone limiting function as provided by the power amplifier IC circuits identified above. For example, amplifier 34 of the preferred embodiment includes four SGS Thompson Model L109 integrated circuits, one for each channel shown in Figure 1. In Figure 3, however, the multiple channels of the preferred embodiment are collectively shown as a single channel including conductors 76 and 78 and a speaker 80. The clipping detector loop 74 provides a clipping detection signal, such as a 0 voltage (low) signal generated by the SGS-L109, when the output of amplifier 34 begins to clip, thereby introducing a significant level of distortion into the output signal. The signal is introduced through an interrupt connection of a signal limiting circuit 31, e.g. via a Texas Instruments TMS 57002, which continuously reduces the signal level supplied to the D/A converter 32 in a linear manner. Such feedback very quickly creates a limit at which the distortion of the amplifier output reaches an acceptable value.

A tone level detector loop 72 is connected to the DSP 28 through a digital multiplexer 33, e.g. through a common logic gate device that performs a two-to-one multiplex. If the detected clipping threshold occurs at a level of the signal 70 that is within a predetermined range corresponding to an acceptable or normal Of course, since the impedance range 90 corresponds to that shown in Fig. 4, the conductors 76 and 78 form a closed circuit between the amplifier and the speaker terminals on the speaker 80. The acceptable range depends on the variable impedance that may be presented by one or more speakers 80 (e.g., the left front speaker 16, the left rear speaker 18, the right front speaker 20, and the right rear speaker 22) connected to the conductors 76 and 78 in each channel (e.g., each pair of conductors of channels 17, 19, 21, and 23 if a single speaker is connected to the conductors at a time), and the total number of channels.

If the microprocessor determines that the level of signal 70 at the cutoff threshold is below the specified normal range, a shorted connection of the loudspeakers would be detected as shown to the left of 90 in Fig. 4. Similarly, if the level is above the specified range 90 when the cutoff threshold is reached, a broken connection would be detected on the pair of conductors intended to connect the respective loudspeaker to the amplifier 34 as shown to the right of 90 in Fig. 4. The microprocessor selects each amplifier channel 17, 19, 21, 23 in turn by setting the gain for that channel to its maximum while setting the gain of the remaining channels to zero by changing the multiplexer constants in the DSP 28.

In response to an amplitude clipping detection, the DSP 28 provides appropriate signals to the microprocessor 27 to transfer control to the microprocessor 29 to generate an appropriate flag on the front panel 12. In particular, the preferred embodiment includes a measurement block 82 which communicates with a program comparator arrangement 86 which determines whether the clipping threshold is at a high, normal or low value, as shown in Figure 4. The microprocessor 27 also reads the refresh byte on the 8-bit parallel bus 84 in order to trigger the generation of a suitable identification on the control panel 12.

In the preferred embodiment, an icon such as an LCD display representing OPEN or UNBR or the like would be illuminated on the display panel 66 to indicate an open circuit condition. An LCD display representing SHRT or SHORT or the like would also be illuminated on the display panel 66 to indicate a short circuit condition. A PASS icon would be illuminated if the diagnostic test indicates a normal condition and therefore a good connection between the amplifier 34 and any speaker in the speaker set 80. If there are multiple speakers in the set, the icons LF or VL (for front left), RF or VR (for front right), LR or HL (for rear left) or RR or HR (for rear right) would similarly appear next to the icon.

In this way, the present invention provides a self-contained diagnostic method and device for determining the status of the speaker amplifier interconnect. The device 10 essentially contains no additional material that would take up space in the dashboard. In addition, the device requires practically only programming rather than components to initiate the initiation of the diagnostic process via the front panel 12 of known DSP radio systems. Only program software needs to be built into the programmable memory of an already known DSP device to realize the control and status display of each speaker connection on the DSP radio.

The present invention thus provides a simple method and system for testing the installation of a communication system, e.g. an entertainment system in a motor vehicle, during the manufacture of the vehicle or during installation of the system, without requiring special diagnostic equipment or additional components in the design of each communication device.

Claims (16)

1. A method for diagnosing an electrical connection between a power amplifier and a loudspeaker in a communication system, comprising: triggering a diagnostic routine by selecting a specified input on a control unit; Generating a predetermined tone signal in response to the selected input; Applying said audio signal to said amplifier; Detecting the output of said amplifier; Changing the level of said audio signal; Monitoring the audio signal level at which clipping occurs at an output of the amplifier; and Indicates whether clipping begins within a specified range of audio signal levels. 2. The method of claim 1, wherein the communication system is a DSP communication device. 3. The method of claim 2, wherein said DSP device is a radio. 4. The method of claim 1, wherein said changing step includes reducing the signal level until clipping ceases. 5. The method of claim 1, wherein said displaying step includes displaying a first indication signal on said control unit when an output having a signal level above said predetermined range is detected; and displaying a second indication signal on said control unit when an output having a signal level below said predetermined range is detected. 6. The method of claim 5, wherein said first indication signal is an indication of a disconnection of the connection. 7. The method of claim 5, wherein said second indication signal is an indication of a short circuit. 8. The method of claim 5, further comprising displaying a third indication signal on said control unit when an output having a signal level within said predetermined range is detected. 9. The method of claim 1, wherein the step of generating includes generating a signal that is generally inaudible to the human ear. 10. The method of claim 9, wherein said step of generating generates a 19 kHz signal. 11. The method of claim 1, wherein said communication system includes multiple loudspeakers, and said method includes sequentially repeating said above steps for each individual loudspeaker. 12. DSP communication system (10) with a diagnostic circuit for diagnosing an electrical connection between a power amplifier (34) and a loudspeaker (16, 18, 10, 22) in the communication system, comprising: an operating unit (12) with means (58, 60, 62) for initiating a diagnostic routine by selecting a predetermined input on the operating unit; a DSP processor unit (28) having programmed means for generating a predetermined test signal in response to said predetermined input and for controlling the magnitude of the test signal; and a D/A converter (32) for applying the test signal to the power amplifier; marked by a detector connected to an output of the amplifier (34) for determining a threshold level above which the amplifier produces a clipped output signal; a monitoring circuit (82, 86) for determining the level of the test signal at the threshold level at which capping is detected; and Means (86) for indicating whether the amplifier (34) is properly connected to a loudspeaker (16, 18, 20, 22) by comparing the detected signal level during clipping with a predetermined range of levels. 13. Communication system according to claim 12, wherein said means for initiating a diagnostic routine comprises means responsive to a keystroke on the control unit. 14. The communication system of claim 13, wherein the key press is a multi-key press. 15. A communications system according to claim 12, wherein the system includes a plurality of audio channels and switch means for serially selecting each of said audio channels for diagnosis. 16. Communication system according to claim 12, 13, 14 or 15, wherein the system is a DSP radio system, the DSP processor unit is designed to generate a test signal formed by an audio signal, and wherein said predetermined range of levels has an upper limit above which the amplifier-loudspeaker connection is interrupted, a lower limit above which the amplifier-loudspeaker connection is short-circuited, and a normal range between said upper and lower limits.