JPS5855457B2 - Pulsed noise test method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pulse noise testing method for electronic equipment such as audio amplifiers.

In the following, an audio amplifier will be described as an example.

The audio amplifier outputs noise with various waveforms depending on the situation.

Figure 1 a = f is a waveform diagram of these various types of noise, and Figure 1 a shows one with a flat frequency spectrum, which is called resistive noise, thermal noise, white noise, etc.

Measuring the average value of this noise is sufficient and poses no problem.

Figures b to f in Fig. 1 are pulse noises, and there is a problem with the evaluation method for these noises.

FIGS. 2A to 2C are noise waveform diagrams for explaining the conventional evaluation method of such pulse noise.

Conventionally, as shown in FIG. 2 a or b, the absolute values r and vN(t
) The first method determines whether the product is good or defective based on the number of times that l exceeds a specified level vN, and the absolute value of the instantaneous value of the output noise during the determination time T as shown in Figure 2C is There is a second method of determining whether a product is good or defective based on the number of times the output noise exceeds k (positive number) times the average value or effective value.

By the way, in the first method described above, the case shown in Figure 2 a is determined to be defective, and the case shown in Figure 2 S is determined to be good, but according to human hearing, it feels the opposite, and the pulse noise is This first
This method is often the opposite of human auditory judgment.

Further, erroneous judgments are likely to occur due to noise from the environment.

On the other hand, the second method shown in FIG.
This method is similar to the change in sensation caused by average noise, where even very small sounds can be felt in quiet places such as in the mountains.

However, in this second method, even if there is wide and loud noise, if the number of times is small, there is a risk that it will be judged as a good product, and erroneous judgments due to noise from the environment are likely to occur.

This invention was made in view of the above points, and focuses only on the "fluctuations" of output noise from stationary noise, and it is possible to make judgments similar to the human auditory sense, and to generate pulse noise that is less susceptible to the effects of environmental noise. It is intended to provide a test method.

FIGS. 3a and 3b are noise waveform diagrams for explaining the present invention in detail.

Figure 3a shows that when the instantaneous value of output noise deviates from the average value or effective value for a long period of time, Figure 3a shows that the instantaneous value of output noise deviates from the average value or effective value for a short time, but frequently. Indicates when this occurs.

This Σ is the average value or effective value (hereinafter abbreviated as "average f button") of the output noise of the audio amplifier under test.

) is vn, the instantaneous value is vN(t), the measurement time is T, the threshold for determining pulse noise is kvN (k>1), and the instantaneous value V N(t) exceeds this threshold kVN. The first step is to determine that the device under test is defective based on the time tN and the time tN.
The reference time is τ1, and the instantaneous value VN (t) is the threshold value kv
A second reference time for measuring the number of times exceeding N is TP1.Let M be a reference number of times for determining that the device under test is defective based on the number of times the test device has been exceeded during this second reference time TPO.

As in the case shown in Fig. 3a, the time tN at which the absolute value VN(t) of the instantaneous noise value vN(t) exceeds the threshold value during the measurement time T is longer than the first reference time τ2. If it is large, it is unconditionally determined to be defective.

As in the case shown in FIG. 3, when the time tN is smaller than the first reference time τ1, I vN(t) I >kv
From time tN to time tN, with the time when H becomes zero as time zero
+Tp, the absolute value vN(t) of the instantaneous value vN(t)
) l exceeded the threshold kvN more than M times (tN〉τ2
If it is negative (-0), it is also determined to be defective.

If the above-described event that is determined to be defective does not occur between time t and time tN+TP, then l VN(t)
Waiting for the occurrence of an event such that 1>kvH, the test method described in FIGS. 3a and 3 above is performed, and this is repeated for a total time T.

If the product is not determined to be defective during time T, it is determined to be non-defective.

FIG. 4 is a block diagram showing an example of an apparatus for carrying out the pulse noise test method of the present invention. In the figure, 1 is an audio amplifier to be tested, 2 is a buffer amplifier for amplifying its output noise, and 3 is an average value. generation circuit, 4 is an absolute value generation circuit, 5 is an analog comparator, 6 is a measurement time setting gate, 7
8 is a pulse width detection circuit, 8 is a gate that sets the pulse number counting time when the pulse width is less than the first reference time, 9 is a counting circuit, and 10 is a display circuit for good and defective products.

Here, if the gain of the absolute value generating circuit 4 is A, the gain of the average value generating circuit 3 is set to be kA.

Output noise from the audio amplifier under test 1 is impedance-converted by a buffer amplifier 2 and supplied to an average value generation circuit 3 and an absolute value generation circuit 4.

The average value generation circuit 3 outputs the average value of the output noise voltage or the smaller value kA of the average values on the positive side and the negative side, and inputs it into one input of the analog comparator 5.

The absolute value generator 4 outputs A times the absolute value of the instantaneous value of the output noise voltage, and inputs it into the other input of the analog comparator 5.

The analog comparator 5 is A l vN(t) l and kA-V
It compares the magnitude with N, that is, the magnitude between IVN(t)I and kvH, and outputs a signal A when lVN(t)1>bN.

The output signal A of the analog comparator 5 is supplied by the gate 6 to the pulse width detection circuit 1 and the counting time setting gate 8 during the measurement time T.

l vH of the output noise added to the pulse width detection circuit 7 (
t) The pulse signal A waveform-shaped under the condition of l>kvH is compared with the first reference time τP by the pulse width detection circuit 7, and if 1N>τ, a defective signal is sent to the display circuit 10. Send.

If tN τ, the pulse width detection circuit 7 sends a second reference time width TPO gate signal to the counting time setting gate 8.

This gate 8 passes the signal I for a time TP and supplies it to a counting circuit 9.

The counting circuit 9 counts the signal A during the time TPO, and sends a defective signal to the display circuit 10 when the counted value is equal to or greater than the reference number 0 described above.

When the counted value is less than the reference number of times M, the counted value is reset.

Although the above example has been described with reference to an audio amplifier, the present invention is generally applicable to equipment that outputs audio frequency voltage.

Furthermore, as I said in the middle of the explanation, I explained it as the average value VN, but this refers to the average value or effective value of the output noise, or the smaller value of the positive side and negative side. .

As detailed above, in this invention, the threshold for determining pulse noise is linked to the above-mentioned VN so that it responds only to the "fluctuation" component of steady noise. If the amount does not reach a predetermined ratio, it will not be judged as defective, and since not only the number of times the pulse noise exceeds the threshold value but also the pulse width is taken into account, the judgment can be made close to the human auditory sense.

In addition, it is less susceptible to environmental noise and reduces misjudgments.

[Brief explanation of the drawing]

Figure 1 a = f is a waveform diagram of various noises, Figures 2 a to C are noise waveform diagrams for explaining the conventional pulse noise evaluation method, and Figures 3 a and b are detailed explanations of the present invention. FIG. 4 is a block diagram showing an example of an apparatus for carrying out the pulse noise test method of the present invention. In the figure, VN is the average value or effective value of the output noise,
kvH is the threshold, tN is the pulse width of pulsed noise, τ
, is the first reference time, TP is the second reference time, and T is the measurement station interval. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] 1 Observe the output noise of the device under test that outputs audio frequency voltage for a specified measurement period, and calculate the instantaneous value of the output noise as VN (
t), the average value or effective value of the above output noise, or the smaller value of these values on the positive side and negative side is VN, and the threshold value for determining the above output noise as pulse noise is 1.
(vN (tabunshik〉1)), the above instantaneous value VN(t
) outputs pulse noise that exceeds the threshold value continuously for a first reference time τ2 or more, and a predetermined number of times between the end of the first pulse noise and the second reference time TPO. A pulse noise testing method characterized in that a device under test is determined to be a defective product when it outputs pulse noise on M recovery.