JPH0695659B2 - Code decoder test method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a code decoder test method capable of testing whether or not the operation of an encoder and a decoder is normal with a simple circuit. Is.

(Prior Art) Conventionally, as a test method for an encoder and a decoder (these are collectively called CODEC), the fourth method is 64 kb / s PCM.
As shown in the figure, an oscillator generates an analog sine wave signal, inputs it to the encoder, folds the digital signal from the encoder back to the decoder, inputs it, and outputs the analog output signal from the decoder with a level meter. By measuring, the normal operation of the encoder and decoder was tested by the analog input / output level difference or S / N ratio.

In addition, a low bit rate CODEC that has been recently developed.
The test method for is described below using the case of 32 kb / s ADPCM as an example. In ADPCM CODEC, a PCM encoder and decoder are used as AD and DA converters that convert analog and digital signals.
EC part is 64kb / s (8bit / sample) digital signal A
The encoding part that encodes at 32 kb / s (4 bits / sample) by the DPCM algorithm and 64 from the encoded code sequence
kb / s digital signal is restored by the decoding unit.
It is configured as a (Digital to Digital) converter.
In this way, in the case of low bit rate CODEC, it is
Since it is composed of a D / D converter, the former is AD here.
And a DA conversion unit, the latter is called an encoding and decoding unit,
They are distinguished by calling them both as a code decoder.
In ADPCM CODEC, the prediction signal is calculated using the past decoded signal and encoding is performed.Therefore, the operation word lengths of the encoding unit and the decoding unit are set to be the same, and transmission / reception is performed by preventing the accumulation of operation errors. Holds synchronous operation. Therefore, the output patterns of the encoding unit and the decoding unit when a constant digital signal sequence pattern is input are uniquely determined. For this reason, CCITT prepares a digital test sequence to confirm the ADPCM algorithm.

(Problems to be solved by the invention) According to the former method, it is necessary to prepare a measuring device such as an oscillator and a level meter and connect it to the CODEC.
If the EC is installed at home or in a remote place, the test becomes difficult. In addition, it was impossible to realize the self-monitoring function to test the CODEC incorporated in the terminal equipment, etc. within the equipment itself.

Also, in the latter method, in order to perform the input / output pattern matching test using the test sequence, several Mb / s or more is required as a memory for storing this, and the CO
It was difficult to apply to DEC self-monitoring.

An object of the present invention is to realize a self-monitoring function capable of performing a low bit rate CODEC test incorporated in a terminal device, a terminal device or the like in its own device by adding a simple circuit.

(Means for Solving Problems) In the present invention, a short-time digital sine wave signal (digitally generated sine wave, for example, PAM waveform) is stored in a memory, and this is repeatedly recorded in a coding unit. When the difference between the level of the output signal of the decoding section and the level of the input sine wave signal is within a certain value, the operation of the code decoding section is normal. Detect and input the above digital sine wave signal to the DA converter,
The output of the converter is input back to the AD converter, and when the difference between the level of the AD converter output signal and the input sine wave signal level is within a certain value, it is detected that the operation of the AD, DA converter is normal. It is characterized by It differs from the conventional technique in that a digital sine wave signal is used and each test is independently performed by the code, decoding unit and DA, AD conversion unit depending on the folding output level.

(Example) The Example of this invention is shown below. FIG. 1 is a block diagram showing the configuration of a low bit rate CODEC, which is an AD converter (A / D) 1 for converting an analog signal into a digital signal, and the digital signal is encoded by a predetermined algorithm such as ADPCM. Coding unit (COD) 2 for decoding, decoding unit (DEC) for restoring a digital signal from a coded code sequence
3, a DA converter (D / A) 4 for converting the digital signal into an analog signal, a test circuit 5 including a storage means for accumulating the digital sine wave signal and a means for detecting the level of the digital sine wave, and a signal path. It is composed of switches 6 to 8 for switching, and is connected to a multiplexing device and the like (not shown) via an interface circuit 9 which performs level conversion and timing adjustment necessary for signal transmission and reception. During normal operation, the analog input signal 10 is converted into a digital signal by the AD conversion unit 1, input to the encoding unit 2, and the coded signal 11 is sent out to the (transmission path side) via the interface circuit 9. It The code sequence 12 input via the interface circuit 9 is restored in the decoding unit 3 and converted into the analog signal 13 in the DA conversion unit 4.
Also, in the case where the AD / DA conversion is performed by another device already connected to the CODEC (for example, a digital exchange) and the digital signal is input / output, the interface is performed via the signal lines 14 and 15 in the figure. A to connect to the circuit
The D, DA converters 1 and 4 and the switch 6 are unnecessary. Usually, the CODEC portions are mounted on the same package, and a number of terminals corresponding to the number of multiplexed channels are mounted in a terminal (multiplexing) device or the like.

At the time of testing the encoding / decoding unit, the signal path in the switches 7 and 8 is set to the path described as T2 by the control signal 16. The control signal 16 may be generated as a remote test signal from the main body of the device in which the CODEC is mounted, or may be generated manually by a push button or the like. After the switching of the signal path is completed, the digital sine wave signal is input from the test circuit 5 to the encoding unit 2, is folded back by the switching unit 8 and passes through the decoding unit 3, and then the digital output signal is taken into the test circuit 5 and the level is To measure. This level is compared with the sine wave signal level stored in the test circuit. If the difference is within a certain range, it is judged that both the encoder and decoder are operating normally, and if it is out of the range. For example, it is determined that some part is out of order (abnormal operation), and the information (result) is output as an alarm signal 17. The alarm signal 17 is used for LED display and the like. Regarding the allowable range of the above level difference, since the characteristics differ depending on the encoding algorithm, the theoretical value or the experimental value of the algorithm used should allow for a margin for variations in the circuit characteristics and be set in advance (usually 1 to 3 dB. Set).

At the time of testing the AD / DA converter, the control signal 16 sets the signal path in the switches 6 and 7 to the path described as T1. After the switching of the signal path is completed, the digital sine wave signal is input to the DA converter 4 from the test circuit. The analog signal output from the DA converter is looped back to the AD converter 1 by the switch 6 and the digital output signal is taken into the test circuit 5 to measure the level. If this level is compared with the sine wave signal level accumulated in the test circuit, and if the difference is within a certain range, it is determined that both AD converter and DA converter are operating normally, and the value is out of range. If so, it is determined that some part is out of order (abnormal operation), and the information (result) is output as the alarm signal 17. The allowable range of the level difference is set in advance (usually set to about 1 dB) in consideration of a margin for thermal noise on the analog line and variations in circuit characteristics. It should be noted that AD / DA conversion has already been performed, and a digital signal is input / output, and a C / D conversion type C
In ODEC, this AD / DA converter test is not required.

The test of the encoding / decoding unit and the AD / DA conversion unit described above is controlled by the control signal 16, but at this time, a 2-bit signal (two signal lines) is used to distinguish between the two. There are two methods: a method and a method of sequentially performing one bit signal (one signal line) in time series, and either method may be used. Similarly, for the return of the test result by the alarm signal 17, the test result of the encoding / decoding unit and the AD / DA conversion unit is represented by a code represented by a 2-bit signal (two signal lines), or 1 A method of sending back by specifying the distinction between the two in time series by a bit signal (one signal line), and
There are two methods of indicating that both are operating normally by a bit signal (one signal line), and either method may be used. An example of the test execution sequence is shown in FIG.

FIG. 3 shows the configuration of the test circuit. It is composed of a memory circuit 18 for accumulating digital sine wave signals, a calculation / comparison circuit 19 for level calculation and comparison, and a control circuit 20 for controlling sine wave reading from the memory circuit and execution of calculation by a control signal 16. Table 1 shows examples of patterns for one cycle of a digital sine wave when the frequency is 800 Hz. This is a well-known pattern clarified by CCITT. Normally, the sample frequency of voice is 8 kHz, and there are 10 types of PCM code here, so if the PCM code is output at this sample rate, the output sine wave will be 800 Hz.

In this way, for example, by storing data of 10 samples and repeatedly reading this, it is possible to obtain a sine wave signal of an arbitrary time length, which is effective in reducing the memory amount.

Normally, all the functions corresponding to the above circuit configuration are realized by a program on a DSP (digital signal processor). Furthermore, since the encoding and decoding units are also digital processing, they can be realized on DSP,
It is even more effective to reduce the size of the circuit by installing both in the same DSP.

(Effects of the Invention) As described above, according to the present invention, the operation confirmation test of the encoder and the decoder in the own device by adding a simple circuit does not require a measuring instrument such as an oscillator and a level meter. There is an effect that can be realized. Moreover, since the AD / DA converter and the code decoder can be tested separately, the characteristics of the failure location are easy, and both analog input / output and digital input / output (D / D conversion) can be performed. It has the advantage that it can be tested against any type of CODEC.

[Brief description of drawings]

1 and 2 are diagrams showing an embodiment of a CODEC test method according to the present invention, FIG. 3 is a configuration example of a test circuit, and FIG.
It is a figure which shows the example of a CODEC test.

Claims (1)

[Claims] 1. An analog signal is converted into a digital signal.
An AD converter, an encoder that encodes the digital signal according to a predetermined algorithm, a decoder that restores the digital signal from the encoded code sequence, and a DA converter that converts the digital signal into an analog signal. And a storage means for accumulating the digital sine wave signal and a means for detecting the level of the digital sine wave. The digital sine wave signal read from the storage means is input to the encoding unit and output from the encoding unit. The code is input to the decoding unit, the level of the digital sine wave output signal output from the decoding unit is detected, the level is compared with the digital sine wave signal level read from the storage means, and the difference is calculated. Is within a certain value, it is detected that the operation of the encoding unit and the decoding unit is normal, and the digital sine wave signal read from the storage unit is DA Input to the conversion unit,
The output signal from the DA converter is input to the AD converter, the level of the digital sine wave output signal from the AD converter is detected, and the level is compared with the digital sine wave signal level read from the storage means. AD when the difference is within a certain value
A code decoder test method characterized in that the operations of the conversion unit and the DA conversion unit are normal.