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JPS52144902

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DESCRIPTION JPS52144902
In the distortion measurement method of input / output characteristic curve of a dual balanced
connection circuit such as a balanced stereo demodulation circuit, an output BLeBR% of the dual
balanced connection circuit to a certain input level B above level B The output ALeAR of the dual
balanced circuit for an input level lower by a certain value and the output CI of a dual balanced
circuit for an input level C higher by a value than the above input level B. Determining the
distortion factor of the double balanced connection circuit by calculating OR and comparing the
average value of the difference between AL and A and H and the difference between OI and CR
with the difference between Bz and BR Characteristic distortion measurement method.
Claims
DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of
measuring the distortion factor of a double balanced connection circuit combining two
differential amplifiers, and in particular to the unbalance of the characteristics of differential pair
transistors constituting the double balanced connection circuit. The present invention relates to a
method of measuring the quality of distortion characteristics based on Generally, when
measuring the linearity of the characteristic curve of a circuit, a sine wave signal is applied to the
input side, harmonics are taken out with a filter on the output side, and the distortion factor is
derived from the ratio of harmonics to the fundamental wave The method is used. However, in
the measurement of the distortion factor by such ac measurement method, it has to be measured
with a signal generator, strain gauge etc. equipped equipment, and in the case of a finished
product with a completely attached terminal, in any case The measurement at the step □ is very
troublesome. Therefore, measurement of the distortion factor by the direct current measurement
method was tried. This is, for example, an output at an operating point level, an output O1 at an
operating point level, a constant one value, an output Oa at an extremely high input level, an
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output Oc at a manual level lower by an operating point level. And 0a-Ob and Ob-Oc. If the two
are equal, it is determined that there is no distortion, and it is determined that the larger the
difference between the two, the larger the distortion. EndPage: 1 However, in order to directly
measure the linearity with respect to such an input / output characteristic curve itself, the
measurement accuracy of the measurement instrument must be extremely high. For example, in
order to check whether the distortion rate conforms to the standard of 0.2% or less, a tester
accuracy of about 0.02% is necessary. In accordance with the mass production pace with such a
high-precision tester It is difficult and impractical to conduct a large amount of strain rate
inspection. The present invention relates particularly to a method of measuring the distortion
factor of a double balanced connection circuit, and the distortion factor characteristic of the
double balanced connection circuit is an imbalance of the characteristics of two differential pair
transistors constituting the circuit as described below. The two differential pair transistors are
simultaneously set under the same bias condition, and the input / output characteristics of the
double balanced connection circuit are measured to determine the distortion factor. In the case
of applying the double balanced connection circuit to a stereo demodulation circuit as shown in
FIG. 1, the inventor of the present invention has almost no distortion rate defect at the time of
stereo signal reception, but has distortion rate defect at the time of monaural signal reception. It
was found that many cases, that is, most distortion defects were distortion defects at the time of
monaural signal reception, and as a result, it was clarified as follows. That is, in the case of
receiving a stereo broadcast, if one of Q2 and Q4 of two switching transistors (two pairs of
differential pair transistors) Q1 to Q4 is shut off, the other Q1 and Q4 are saturated, then In the
moment of the moment, it is impossible that the problem of the imbalance of the transistors
mutually becomes an issue at the moment, but in the case of receiving a monaural signal, the
terminals A and B + are shorted and differential The same potential is applied to the input of each
switching transistor, which is a pair transistor, so that the current is shared by half of the
differential pair transistors.
However, some characteristic differences in the differential pair transistors tend to result in
deterioration of the linearity of the input / output characteristics at the time of monaural signal
reception and high distortion factor when the balance becomes worse. It becomes. Figure 5 (-)
and (→ are those with good distortion rate (a) and bad one (1)) to verify this, the input and
output characteristic curves for each of the left and right channels in Figure 1 are examined with
a curved laser It is a characteristic curve figure. As apparent from this, it can be considered that
the input / output characteristics of the left and right channel do not match, and the balance of
the differential pair transistors is bad when the monaural signal is received with a low distortion
factor. Therefore, the distortion factor can be estimated by examining the balance of the left and
right channels without strictly checking the input / output characteristic curve itself. The present
invention has been made under such recognition, and an object of the present invention is to
simply measure the distortion factor of the input / output characteristics of a double balanced
connection circuit consisting of two sets of differential amplifiers. According to one embodiment
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of the present invention, in the distortion factor measurement method of the input / output
characteristic curve of the double balanced connection circuit, the outputs BL of the left and right
channels with respect to a certain input level B. BR1 For the input level A which is lower than the
above level. The outputs OL and OR of the left and right channels with respect to the output ATtAR of the left and right channels and the input level 0 higher by a certain value than the above
input level B are obtained, and the average value of AI, ARO difference and CI, and CR difference
To determine the distortion rate by comparing the difference between BL and BR. Hereinafter,
the present invention will be described based on a specific example in which a double balanced
connection circuit is used for a balanced stereo demodulation circuit. FIG. 1 shows a balanced
stereo demodulation circuit to be subjected to distortion measurement according to the present
invention. A differential amplifier consisting of a switching transistor Q1sQ2, a load resistor RLLs
RLR and an amplifying transistor Q is a cancellation circuit of a crosstalk component consisting
of a switching transistor Q *, Q, a, an amplifying transistor q6 and resistors R1 to R. Provided to
complete separation of the left and right channels. R4とR,はQ6. Resistance that biases Qs.
When receiving a stereo signal, the switch SW is on the S side, and a switching pulse vso (38KH,)
is applied between the A and B terminals by superimposing on the DC reference voltage ■
R111ν applied to the A terminal, EndPage: Q2 μi is turned on and Q1 # Q4 is turned off at two
timings, and Q2 pQl is turned off and Qll Q4 is turned on at the next timing.
When a monaural signal is received by this stereo demodulation circuit, the switch SW is
switched to the M side, and the same bias is applied to all the bases of the switching transistors
Q1 to Q4 to turn them all on. As described above, when all the switching elements are turned on
to receive monaural signals, for example, if there is variation in the characteristics of the
switching transistor, current flows uniformly to the differential pair transistors of the differential
amplifier. There is a problem of monotonic THD (Total Harmonic Distortion). As a result of
measuring the input / output characteristic curve for each of the left and right channels with
respect to the non-defective product which passed the monaural THD test with respect to each of
the left and right channels with the curve tracer, all the former (non-defective product) The latter
(defective product) is also apparent from, for example, a mismatch as shown in the figure (bl),
that is, an imbalance between the left and right channels occurs. Therefore, as shown in FIG. 2,
the outputs BL of the left and right channels with respect to the input B of the operating point
level, the outputs ALjAR of the left and right channels with respect to the input A of the lower
limit level of the BR1 dynamic range, and the left and right channels with respect to the input C
of the upper limit level of the dynamic range. Measure the output CLtOR. Then, a calculated value
V D representing the distortion factor is obtained by the following equation%). Then, the
distortion factor is determined to be larger as the absolute value of the calculated value VD is
larger. That is, the poor linearity of the input / output characteristic curve in monaural in the
differential amplification type stereo demodulation circuit is due to the unbalance of the
characteristics of the switching transistors forming the differential pair. Therefore, in the case
where the characteristic is unbalunable, for example, having the characteristic shown in FIG. 2 as
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an example, input A (input level corresponding to upper limit of dynamic range), input B
(operating point level), input C (dynamic range lower limit) If you check the output ALsARpBLsBR
* CLsCR for the input level 5 that corresponds to the above, AI, AR is AR ', and, even though oL is
higher than CR, BTJO is lower P) R lower It is. This indicates that the characteristic curves of both
left and right channels are distorted. The distortion is considered to be thicker as the distortion is
greater. That is, according to the present invention, the distortion is obtained by subtracting the
difference between the left and right outputs of the operating point level at the normal time from
the difference between the left and right outputs at the upper limit of the dynamic range and the
difference between the left and right outputs at the lower limit. It is to estimate.
Further, in the case of FIG. 3 (a) which is not caused by poor linearity, since the average value of
AL-AR and aTJ-cR is equal to BL-BR, and the calculated value is approximately O, the distortion
factor is defective. Is not determined. Similarly, in the case of FIG. 3 (ii), since (ALAR) + (OLOR) is
0 and BL-BR is also 0, it is determined that the distortion rate with a calculated value of 0 is not
defective. As described above, the measurement method of the present invention makes it
possible to distinguish between those with low distortion and those with good distortion. Of
course, the cases of FIG. 3 (a) and (b) should also be distinguished from non-defective products
that are defective. However, it should not be rejected in the strain rate test. Thus, according to
the present invention, the quality of distortion can be determined. FIG. 4 shows the relationship
between the distortion factor (MoNo, Tu: o) at the time of receiving a monaural signal and the
calculated value by the distortion factor measurement according to the present invention for a
semiconductor bellet in which several circuits of FIG. 1 are integrated. In the correlation diagram
shown (where the abscissa is the value of the strain rate measured strictly by the strain rate
measuring device and the ordinate is the calculated value measured by the measuring method of
the present invention), a shows an ideal straight line. If the experiment is on the diagram, it is
perfect. The further away it is from the straight line, the less complete. From this test result, it
can be said that, according to the present invention, the EndPage: 3 position which is extremely
close to the ideal straight line is correct even if it is not perfect. Of course, the smaller the strain
歪 value, the larger the ratio of the difference between the measured value according to the strict
measurement method and the measured value according to the present invention. do not have to.
Therefore, it can be said that there is virtually no difference in judging the acceptance or
rejection of the distortion factor according to the present invention. According to the present
invention, strain rate test can be performed only by calculation processing for measurement
results at three levels, and it is necessary to measure IJ nearness of the characteristic curve
strictly by dynamic measurement. The distortion factor can be easily measured. It is not
necessary that the input levels A, B, 0 as measurement points correspond to the dynamic range
lower limit level, the operating point level, and the dynamic range upper limit level, and A> B> 0%
6 or A (B <0 It should be O. That is, even if the level of the input cam is slightly higher than the
dynamic range lower limit level, the level of C may be slightly lower than the upper limit level
even if B slightly deviates from the operating point level. The present invention is not limited to
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the measurement of the distortion factor of the demodulation circuit, but is generally applied to a
double balanced connection circuit consisting of two sets of nine differential amplifiers.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an example of a stereo demodulation circuit to
be measured according to the present invention, and FIG. 2 is an input / output characteristic
curve diagram of left and right channels in a circuit with a distortion factor failure; b) shows the
input / output characteristic curves of the left and right channels showing an example of a defect
that is not a defect in distortion, and FIG. 4 shows the relationship between the measured values
of severe distortion for some pellets and the measured values according to the present invention
It is a correlation diagram. FIG. 5 compares input / output characteristic curves of left and right
channels of a non-defective product and a non-defective product regarding distortion factor, and
(&) indicates a non-defective product. RLLeRLR · · · Load resistance, R1-R · · · · Resistance, Q1-Q6 ·
· · Transistor,-C · · · DC output, E · · power supply for bias, vco · power supply voltage, vsc · ·
subcarrier signal, VRIF · · DC reference voltage. Jキ? ・。 Attorney Attorney Attorney 1)
Toshiyuki. 1st 8c 3 c ˜ ˜) ■ Person EndPage: 4 5 5. (2) (b) input level 11 □ OOl Q-5, 1, or 5Y = I
group L ')? MONO, chome U) (ヅ EndPage: 5
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