JPH0246014A - Non-linear amplifier circuit and non-linear emphasis/ deemphasis circuit using the same - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Object of the Invention] (Industrial Application Field) The present invention relates to a nonlinear amplifier circuit and a nonlinear emphasis/deemphasis circuit using the same.

(Prior Art) Generally, in a VTR (video tape recorder) or a video disc, a video signal is FM modulated and recorded. When recording, reproducing and demodulating an FM modulated signal,
The noise distribution after FM demodulation increases as the frequency increases. Emphasis/de-emphasis is used as a method for suppressing this triangular noise and improving the S/N ratio.

This uses an emphasis circuit to emphasize (emphasis) the high-frequency components of a video signal and performs FM modulation, and during demodulation, a de-emphasis circuit with characteristics opposite to the emphasis characteristics suppresses the high-frequency components.

Emphasis characteristics are limited by the transmission band of FM waves,
If the S/N emphasis amount is too large, a so-called inversion phenomenon occurs in which the white peak of the video signal drops to the black level. Nonlinear emphasis has been devised as a method to avoid this inversion phenomenon and further improve the S/N ratio. This nonlinear emphasis is a method that reduces the amount of emphasis when the video signal amplitude is large, and increases the amount of emphasis when the amplitude is small. For example, literature: National T
electrical report Vol. 25 No.
, I Peb, 1979 '4 hour recording VH8 system VT
15, the nonlinear emphasis circuit described in this document includes resistors R11 and R12, capacitors C1l and C12, and diodes D11 and D12 as nonlinear elements. The values of resistors R11 and R12 and capacitors C11 and C12 are expressed by the same symbol, and the resistance value of diodes Dll and D12 is expressed as R13, and further R1
1-C11-Rl2-CI2, the transfer function Gl(S) is expressed by the following equation.

Here, if the input signal amplitude is large, the diode Dll
, D12 becomes conductive, so that G 1(s)=
R12/(R11+R12) -■.

Also, when the input signal amplitude is small, 1! in the low frequency region! i ta Gl(s)= R12/ (R11+
R12) -■S→0, and in the high frequency region, I its Gl(s)-1-■S.The frequency characteristics in these cases of (1) to (2) are shown in FIG.

On the other hand, a nonlinear de-emphasis circuit with characteristics opposite to the nonlinear emphasis circuit in FIG. 15 can be realized by inserting the nonlinear emphasis circuit in FIG. 15 into the negative feedback loop of an amplifier with a sufficiently large gain A, as shown in FIG. 17. be done. Transfer function 02 (
s) is G2(s)=A/(1+G1(s
)1, and if A is made sufficiently large, it becomes G 2 (s) + 1 / G 1 (s).

However, in the nonlinear emphasis circuit shown in FIG.
In order to obtain a nonlinear emphasis characteristic of up to 28 dB or more, it is necessary to make the input signal level sufficiently high using an amplifier in advance so that the nonlinear region of the diode can be utilized even in the minute level region. As a result, if the original signal amplitude is large, the signal amplitude in the emphasis circuit becomes excessive, which causes problems such as the need to increase the withstand voltage of the diodes Dll and D12, and the need to increase the power supply voltage. arise.

In addition, in the nonlinear de-emphasis circuit shown in Figure 17, it is ideal that the gain A of the amplifier is infinite, but in reality the gain A takes a finite value, and especially at high frequencies, the group delay characteristics and frequency characteristics deteriorates. Therefore, the first
A nonlinear de-emphasis characteristic completely opposite to that of the nonlinear emphasis circuit shown in FIG. 5 cannot be obtained. If the non-linear emphasis characteristic and the non-linear de-emphasis characteristic are not completely opposite characteristics, ringing will occur in the reproduced video signal after FMm modulation, and the waveform characteristics will deteriorate. As a result, particularly in VTRs, image quality deterioration becomes noticeable when dubbing is repeated.

(Problems to be Solved by the Invention) As mentioned above, in conventional nonlinear emphasis/deemphasis circuits, when trying to achieve emphasis characteristics down to the minute level region of the input signal, the signal amplitude in the circuit becomes excessive and the diode It is necessary to increase the withstand voltage of the circuit or increase the power supply voltage, and due to the deterioration of group delay characteristics and frequency characteristics at high frequencies, it is not possible to make the emphasis circuit and de-emphasis circuit completely opposite characteristics. There was a problem that signal quality was compromised.

The present invention was made to solve these problems, and its purpose is to create a nonlinear system that can obtain nonlinear emphasis and deemphasis characteristics even in the minute level region of the input signal without increasing the signal amplitude in the circuit. The purpose of the present invention is to provide an amplifier circuit.

Another object of the present invention is to provide a nonlinear emphasis/deemphasis circuit that uses such a nonlinear amplifier circuit and can accurately obtain opposite characteristics.

[Structure of the Invention] (Means for Solving the Problems) The nonlinear amplifier circuit according to the present invention first includes a low-pass removal filter that receives an input signal from an input terminal, and an output signal of the low-pass removal filter. A logarithmic amplifier consisting of a bidirectional logarithmic element and a resistor is connected in parallel between an receiving amplifier and an input/output terminal 1 of the amplifier, and the output signal of this logarithmic amplifier and the input signal are added with a predetermined polarity relationship. The present invention is characterized in that it includes an adder that generates an output signal using the input signal and sends the output signal to an output terminal.

Second, the nonlinear amplification circuit according to the present invention includes a low-pass removal filter, an amplifier that receives the output signal of the low-pass removal filter, and a bidirectional logarithm connected in parallel between the input and output terminals of the amplifier. A logarithmic amplifier consisting of an element and a resistor, an output signal of this logarithmic amplifier and an input signal from an input terminal are added with a predetermined polarity relationship to generate an output signal, and the output signal is applied to the low-pass removal filter and the output terminal. It is characterized in that it is equipped with an adder that sends data to.

Here, the bidirectional logarithmic element has a voltage of - in both the positive and negative directions.
This is an element whose current characteristics are logarithmic.

Further, the resistor connected in parallel with the bidirectional logarithmic element to the amplifier is used to determine the gain of the logarithmic amplifier in a region where the signal frequency is high and the amplitude is small. In any of these nonlinear amplifier circuits, if the output signal of the logarithmic amplifier and the human input signal from the input terminal are added in the adder with the same polarity, it becomes a nonlinear emphasis circuit, and if they are added with opposite polarity, it becomes a nonlinear deemphasis circuit. In other words, when the frequency of the input signal is low, the output voltage of the low-pass filter and the logarithmic amplifier is almost 0 regardless of the amplitude of the input signal, so the input signal is almost unchanged at the output of the adder. However, when the frequency of the input signal is high, the output voltage of the low-pass filter and logarithmic amplifier path becomes the voltage obtained by logarithmically converting the human input signal voltage, so the output of the adder has the amplitude of the input signal. The smaller the amplitude, the more emphasized or attenuated a signal can be obtained.

Furthermore, the nonlinear emphasis/deemphasis circuit according to the present invention provides a nonlinear It is characterized in that it is used as an emphasis circuit, and the other is used as a nonlinear de-emphasis circuit. In this case, in the first nonlinear amplifier circuit, a delay element is inserted in the signal path from the input terminal to the adder via the low-pass rejection filter and the logarithmic amplifier, and the delay time of this delay element and the second nonlinear amplifier circuit are The delay time of the adder is made almost the same as that of the adder.

In addition, when configuring such a nonlinear emphasis φ de-emphasis circuit, one low-pass removal filter is shared as a low-pass removal filter in the first and second nonlinear amplifier circuits, and one logarithmic amplifier is also used in common. It is desirable to do so.

(Function) In the nonlinear amplifier circuit according to the present invention, since the logarithmic element is connected between the input and output terminals of the amplifier, if the gain of the amplifier is large to a certain extent, the nonlinearity of the logarithmic element can be avoided without increasing the input signal level more than necessary. The area can be used effectively and the amount of emphasis can be increased. Furthermore, the signal amplitude within the circuit does not become excessive, and it is possible to lower the withstand voltage and power supply voltage of the logarithmic element.

Furthermore, in the present invention, both the nonlinear emphasis circuit and the nonlinear de-emphasis circuit are configured to obtain an output signal by adding the input signal and the signal that has passed through the path of the low-pass rejection filter and the logarithmic amplifier. Unlike the method of realizing a nonlinear de-emphasis circuit by inserting it into a negative feedback loop, the gain of the amplifier is not required to be infinite as a condition for making the non-linear emphasis/de-emphasis characteristics opposite to each other. Nonlinear emphasis/deemphasis characteristics with opposite characteristics are obtained.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a nonlinear amplifier circuit according to an embodiment of the present invention. In the same figure, an input signal X (s) supplied from an input terminal 11 is filtered by a low frequency removal filter 12 (; after low frequency components including DC components are removed, an input signal X (s) is passed between the input and output terminals of an amplifier 13. The output signal of the logarithmic amplifier 16 is inputted to a logarithmic amplifier 16 in which a tropic logarithmic element 14 and a resistor 15 are connected in parallel.The output signal of the logarithmic amplifier 16 is inputted to an adder 17, and the input signal X (s)
and are added in a predetermined polarity relationship. The output signal Y (s) of this adder 17 is guided to an output terminal 18 .

FIG. 2 shows a specific example of the bidirectional logarithm element 14.
a) is an example of two diodes connected in antiparallel;
b) is an example of two so-called diode-connected transistors connected between the collector and base in antiparallel;
FIG. 2C shows an example in which two transistors whose bases are at ground potential are connected in antiparallel. In addition, various other configurations are possible, such as one in which temperature compensation is performed by controlling the base potential of the transistor.

When the nonlinear amplifier circuit shown in FIG. 1 is used as a nonlinear emphasis circuit, the output signal of the logarithmic amplifier 16 and the input signal X (s) may be added in the adder 17 with the same polarity. In this case, the low-pass rejection filter 12 and the logarithmic amplifier 1
Let the overall transfer characteristic of 6 be H(s), and input signal X(s
) and output signal Y (s) respectively as X 1(s),
If Y 1(s), then Yl(s) = (1+H(s)
l -Xl(s) . . . -(L), and its characteristics are as shown in FIG.

On the other hand, when the nonlinear amplifier circuit of FIG. 1 is used as a nonlinear de-emphasis circuit, the output signal of the logarithmic amplifier 16 and the input signal X (s) may be added with opposite polarities in the adder 1°7. In this case, input signal X (s) and output signal Y (s) are expressed as X 2 (s) and Y 2 (
s), then Y2(s)-(1-H(s))-X2(
s) -C2>, and its characteristics are as shown in FIG.

FIG. 5 shows FIG. 1 more specifically, and the low-pass removal filter 12 is composed of a series circuit of a capacitor 51 and a resistor 52. Further, the amplifier 13 is an inverting amplifier, a non-inverting input terminal is grounded, and a logarithmic element 14 and a resistor 15 are connected in parallel between the inverting input terminal and the output terminal. In this case, the inverting input terminal of the amplifier 13 is in a virtual ground state. Note that, for example, OB+2920 is known as a logarithmic amplifier IC incorporating an inverting amplifier 13 and a logarithmic element 14.

FIG. 6 is a diagram for explaining the operation of the nonlinear amplifier circuit shown in FIG. is expressed by the following equation.

becomes. However, V e (s) is the error voltage at the inverting input terminal of the amplifier 13.

Moreover, the current I2 flowing through the resistor 15 is further calculated by the bidirectional logarithmic element 1 when the output voltage of the amplifier 13 is V (s).
If the resistance value of 4 is Rd, then if the parallel composite impedance of the logarithmic element 14 and the resistor 15 is 22 (s), then the input terminal 11 is
), the current 1 (S) flowing through the capacitor 51 and the resistor 52 is I 1 ( s)+12
(s) + 13(s) = 0 If the gain of the amplifier 13 is -, V (s) −−K −Ve(s) Equation (8) From (9)... (9) Here, the amplifier 13 If the gain -K of 13 is set sufficiently large, 2-Rd From equations (5) and (6), R2-12(s)-Rd -13(s)
-(12), and for example, in the case of the OEI 2920, the input current 13 (s) and the output voltage have the characteristics shown in FIG. 7, and the relationship between l3 (s) and Rd is uniquely determined. Furthermore, from equation (12), 12(s) is also determined as -. Therefore,
The output voltage V (S) of the logarithmic amplifier 16 is: (a) When the frequency of the input signal is low, it is s-0, so V (s) "= 0
...(13) (b) When the frequency of the input signal is high and the amplitude is small, S-+Flash, Rd-■, (c) When the frequency of the input signal is high and the amplitude is large, S→■
, Rd→0, so it becomes.

Therefore, at high frequencies, as shown in FIG. 8, a nonlinear emphasis characteristic can be obtained in which the gain is high when the input signal has a small amplitude, and the gain is low when the input signal has a large amplitude. Furthermore, as is clear from this figure, the nonlinear emphasis characteristic is obtained even in the region where the input signal amplitude is extremely small, about 140 dB.

Here, the logarithmic element 14 is connected between the input and output terminals of the amplifier 13, and even when the input signal amplitude is small, the potential difference between the two terminals is large, so the diode or transistor is easily turned on. Therefore, the nonlinear region of the logarithmic element 14 can be used without increasing the input signal amplitude unnecessarily as in the conventional case, so the voltage inside the nonlinear amplifier circuit can be reduced, and the logarithmic element 14 can be used. The withstand voltage of the diodes and transistors forming the structure may be low, and the power supply voltage of the amplifier 13 may also be low.

FIG. 9 shows another example embodying the nonlinear amplification circuit shown in FIG. The connection point with 62 is the amplifier 13
is connected to the non-inverting input terminal of Furthermore, amplifier 1
A resistor 63 is connected between the inverting input terminal of No. 3 and ground.

The resistor 63 and the resistor 15 determine the gain of the logarithmic amplifier 6. In the nonlinear amplifier circuit shown in FIG. 5, the output signal of the low-pass rejection filter 12 is given to the amplifier 13 as a current signal, and is converted from current to voltage in the amplifier 13, whereas in the nonlinear amplifier circuit shown in FIG. The basic difference is that the output signal of the low-pass removal filter 12 is applied to the amplifier 3 as a voltage signal, and the effects are the same.

FIG. 10 shows a nonlinear amplifier circuit according to another embodiment of the present invention. In the figure, a low-pass removal filter 22, an amplifier 23. Bidirectional logarithmic element 24. A logarithmic amplifier 26 consisting of a resistor 25 and an adder 27 are composed of the low-pass removal filter 12, the amplifier 13, the bidirectional logarithmic element 14 . This is the same as the logarithmic amplifier 16 consisting of a resistor 15 and the adder 17.

In this embodiment, the input signal E supplied from the input terminal 21
(s) is applied to one input terminal of the adder 27, and is added to the output signal of the logarithmic amplifier 26 with a predetermined polarity relationship. Then, the output signal F (s) of the adder 27 is guided to the output terminal 28, and the low-pass removal filter 2
2 is input. The output signal of the low-pass removal filter 22 is input to a logarithmic amplifier 26.

When the nonlinear amplifier circuit of FIG. 10 is used as a nonlinear de-emphasis circuit, the output signal of the logarithmic amplifier 26 and the input signal E (s) may be added in the adder 27 with opposite polarities. In this case, as in FIG. 1, the overall transfer characteristic of the low-pass filter 22 and the logarithmic amplifier 26 is H(s), and the input signal E(s) and output signal F(s) are each E1(s). , F 1(s), then F L(s) −E 1(s) −H(s)
From reference F1(s)-(16), it becomes, and its characteristics are almost the same as in Fig. 4.

Here, consider a case where the nonlinear amplifier circuit of FIG. 1 is used as a nonlinear emphasis circuit, and the nonlinear amplifier circuit of FIG. 10 is used as a nonlinear de-emphasis circuit. In this case, it is assumed that the output signal Yl(s) of the nonlinear emphasis circuit with the configuration shown in FIG. 1 is equal to the input signal El(s) of the nonlinear deemphasis circuit with the configuration of FIG. s)), substituting equation (L) into equation (17) yields -X 1(s)
...(18), and the input signal X1(s) of the nonlinear emphasis circuit and the output signal F1(s) of the nonlinear deemphasis circuit match. In other words, the characteristics of nonlinear emphasis and nonlinear deemphasis can be completely reversed.

On the other hand, when the nonlinear amplifier circuit of FIG. 10 is used as a nonlinear emphasis circuit, the output signal of the logarithmic amplifier 26 and the input signal E (s) may be added in the adder 27 with the same polarity. In this case, input signal E (s) and output signal F (s) are expressed as E 2 (s) and F 2 (
s), then F 2(s) −E 2(s) + H(
s) ・F 2(s) − (19) From this, the following is obtained, and the characteristics are almost the same as those shown in FIG.

Here, consider a case where the nonlinear amplifier circuit of FIG. 10 is used as a nonlinear emphasis circuit, and the nonlinear amplifier circuit of FIG. 1 is used as a nonlinear de-emphasis circuit. In this case, the output signal F2(s) of the nonlinear emphasis circuit with the configuration shown in FIG. 10 and the human input signal X2(s) of the nonlinear de-emphasis circuit with the configuration shown in FIG. 1 are assumed to be equal. X2(s)), substituting equation (20) into equation (2) yields -E2(s)...(21), and the input signal E2(s) of the nonlinear emphasis circuit
) and the output signal Y2 (S
) matches. In other words, the characteristics of nonlinear emphasis and nonlinear deemphasis can be completely reversed.

Although the delay time in the circuit has been ignored in the above explanation, since delays actually exist, the transfer function will differ slightly from the above. FIG. 11 shows the nonlinear amplifier circuit of FIG. 1 in which a delay element 19 for delay compensation is inserted between the logarithmic amplifier 16 and the adder 17. Note that the position of the delay element 19 is not limited to this, and may be placed anywhere in the signal path from the input terminal 11 to the adder 17 via the low-pass removal filter 12 and the logarithmic amplifier 16.

Here, the nonlinear amplifier circuit in Fig. 11 is converted to nonlinear! Consider a case where the nonlinear amplifier circuit of FIG. 10 is used as a nonlinear de-emphasis circuit. now,
As shown in FIG. 12, the transfer function of the low-pass filter 12 and logarithmic amplifier 16 in FIG. 11 is expressed as H(s).
, the delay time is τ■, the delay time of the adder 17 is τ2, and the delay time of the delay element 19 is τ3, then (X(s)+H(s)・e”s”・X(s)le
-Y(s), e -τ2S (1+H(s) ・e ”' +r3”) e-72
' ・X(s) −Y(s) −(22) Also, the 13th
As shown in the figure, the low-pass removal filter 22 in FIG.
If the transfer function of the logarithmic amplifier 26 is H(s), the delay time is τ11, and the delay time of the adder 27 is τ2, then 1τis −τ2S (Y(s) −H(s) ・e −Z(s) )l
e −Z(s)−τls τ2s Y(s) = (H(s) ・e +e
) By substituting equation (22) into Z(s) equation (23), it is clear from equation (24) that the nonlinear emphasis circuit with the configuration of FIG. 11 and the nonlinear de-emphasis circuit with the configuration of FIG. The total delay time is determined by adder 17.
27 total delay time 2τ2. Also, formula (24)
As is clear from the first term on the right-hand side, τ3−τ2
In other words, if the delay time of the adder 27 and the delay time of the delay element 19 are made equal, the output signal Z (s) of the nonlinear de-emphasis circuit is simply the delayed input signal X (S) of the non-linear emphasis circuit, This shows that the nonlinear emphasis circuit and the nonlinear deemphasis circuit have completely opposite characteristics.

In this way, the nonlinear amplifier circuit of FIG. 11 in which the delay element 19 is added to that of FIG. 1 is used as a nonlinear emphasis circuit,
By using the nonlinear amplifier circuit shown in FIG. 10 as a nonlinear de-emphasis circuit, the emphasis characteristic and the de-emphasis characteristic can be made completely opposite characteristics even if the delay within the circuit is taken into consideration.

It goes without saying that the same effect can be obtained when the circuit shown in FIG. 10 is used as a non-linear emphasis circuit and the circuit shown in FIG. 11 is used as a non-linear de-emphasis circuit, contrary to the above.

Incidentally, it is desirable that the total delay time τ1 of the low-pass removal filter 12 and the logarithmic amplifier 16 in FIG. 12 be shorter than a half cycle of the highest frequency component of the input signal. In FIG. 12, the delay time τ3-0 of the delay element 19 is considered. Now, assume that a component of the highest frequency fs of an input signal (for example, a video signal) is input to the input terminal 11. When the total gain of the low-pass filter 12 and the logarithmic amplifier 16 is 1, and the addition ratio of the adder 17 is 1=1, the output signal y (t) expressed as a function of time is y (t) = sln ( 2πfm t)+5in12πfa
r(t+rl)1...(25) The period TI of the highest frequency component of the input signal is Tn -1/
fm...(2B) Here, if 1/2 of the period TIl is equal to rl, τl■Ts+/2 = 1/2 f tp...
・(27) Substituting equation (27) into equation (25) gives )'
(t) −5in(2πfts t) +51n(2z
fm t +π)−sin(2πf tx t )−
sin(2πf@t)−〇, and the input signal cannot be transmitted.

If rl>1/2fo+, y(t)-0 does not occur, and the input signal can be transmitted correctly.

On the other hand, in the configuration shown in FIG.
The total delay time of 2, the logarithmic amplifier 26, and the adder 27 may be made shorter than a half cycle of the highest frequency component of the input signal.

By the way, as is clear from comparing the nonlinear amplifier circuits in Figures 10 and 11, both circuits use a low-pass filter, a logarithmic amplifier, and an adder as components, so some of these Or you can share everything.

Figure 14 shows the low-pass removal filter 11.2 in Figure 10.
This figure shows the configuration of a nonlinear emphasis/de-emphasis circuit that shares one low-pass rejection filter and one logarithmic amplifier as 16.26 and 16.26, respectively.The input/output terminals of the emphasis circuit are 11.18, and the de-emphasis The input and output terminals of the circuit are 21.28. Here, when the changeover switches 31 and 32 are connected to the side shown by the solid line, the low-pass rejection filter and logarithmic amplifier are used for the emphasis circuit, and when the changeover switches 31 and 32 are connected to the side shown by the broken line, the low-pass rejection filter and logarithmic amplifier are used for the emphasis circuit. A band rejection filter and a logarithmic amplifier are used in the de-emphasis circuit.

By sharing the low-pass removal filter and the logarithmic amplifier between the emphasis circuit and the de-emphasis circuit in this way, the configuration of the entire non-linear emphasis/de-emphasis circuit can be simplified, which is advantageous in terms of cost. Further, there is no need to consider the difference in characteristics when a low-pass removal filter and a logarithmic amplifier are separately provided in both circuits, and the emphasis/de-emphasis characteristics can be more completely reversed.

In Fig. 14, the circuit shown in Fig. 11 is used for the nonlinear emphasis circuit, and the circuit shown in Fig. 10 is used for the nonlinear de-emphasis circuit, but conversely, the circuit shown in Fig. 10 is used for the nonlinear emphasis circuit, and the circuit shown in Fig. Even when the circuit shown in FIG. 11 is used, the low-pass removal filter and the logarithmic amplifier can be shared.

In addition, the present invention can be implemented with various modifications without departing from the scope of the invention.

[Effects of the Invention] The nonlinear amplifier circuit according to the present invention has a configuration in which an input signal and an input signal or an output signal passed through a low-pass filter and a logarithmic amplifier are added with a predetermined polarity relationship to produce an output signal. , a nonlinear amplification operation can be obtained from a region where the input signal has an extremely small amplitude without increasing the input signal level more than necessary. Therefore, S/N
Even if the emphasis amount (de-emphasis f:k) is increased in order to enhance the improvement effect, there is no fear that the signal amplitude in the circuit will become excessive, and it is possible to lower the withstand voltage and power supply voltage of the logarithmic element.

Furthermore, the nonlinear emphasis/deemphasis circuit according to the present invention includes a feedforward configuration that guides the input signal to a path of a low-pass removal filter and a logarithmic amplifier,
It consists of a first nonlinear amplifier circuit in which a delay element is inserted in the path from the input terminal to the adder via the low-pass rejection filter and the logarithmic amplifier, and a feedback configuration that guides the output signal to the path of the low-pass rejection filter and the logarithmic amplifier. , one of the second nonlinear amplifier circuits whose adder delay time is approximately the same as the delay time of the delay element in the first nonlinear amplifier circuit is used as a nonlinear emphasis circuit, and the other is used as a nonlinear deemphasis circuit. Accordingly, the characteristics of the nonlinear de-emphasis circuit and the non-linear de-emphasis circuit can be accurately reversed. Therefore,
It can prevent signal quality deterioration due to non-linear de-emphasis/de-emphasis characteristic mismatch, especially for VTRs.
In this case, image quality deterioration can be kept to a minimum even when dubbing is performed multiple times.

Furthermore, by sharing the low-pass rejection filter and logarithmic amplifier between the nonlinear emphasis circuit and the nonlinear de-emphasis circuit, the circuit configuration can be simplified and costs can be reduced. The symmetry between the emphasis and de-emphasis characteristics is not impaired due to the non-uniformity of the characteristics, and even better non-linear emphasis/de-emphasis characteristics can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a configuration of a nonlinear amplifier circuit according to an embodiment of the present invention, FIG. 2 is a diagram showing a specific example of a bidirectional logarithmic element, and FIG. 3 is a diagram showing characteristics of a nonlinear emphasis circuit based on the present invention. 4 is a characteristic diagram of the nonlinear de-emphasis circuit based on the present invention, FIG. 5 is a diagram showing a more specific example of FIG. 1, and FIG. 6 is a diagram for explaining the operation of FIG. 5. , 7th
Figure 8 shows the characteristics of a known logarithmic amplifier, Figure 8 shows the characteristics of the logarithmic amplifier in this embodiment, Figure 9 shows another example that is more specific than Figure 1, and Figure 10. FIG. 1 is a diagram showing the configuration of a nonlinear amplifier circuit according to another embodiment of the present invention.
1 is a diagram showing the configuration of a nonlinear amplifier circuit according to yet another embodiment of the present invention, FIG. 12 is an equivalent circuit diagram of FIG. 11, FIG. 13 is an equivalent circuit diagram of FIG. 10, and FIG. 14 is an equivalent circuit diagram of FIG. 15 is a diagram showing the configuration of a conventional nonlinear emphasis circuit; FIG. 16 is a diagram showing its characteristics; FIG. 15 is a diagram showing the configuration of a conventional nonlinear emphasis circuit;
FIG. 17 is a diagram showing the configuration of a conventional nonlinear de-emphasis circuit. 11... Input terminal (first input terminal), 12... Low-pass removal filter (first low-pass removal filter) 13...
Amplifier, 14... Bidirectional logarithmic element, 15... Resistor, 16... Logarithmic amplifier (first logarithmic amplifier), 17.
... Adder (first adder), 18... Output terminal (first output terminal), 19... Delay element, 21... Input terminal (second input terminal), 22... -Low-pass removal filter (second low-pass removal filter), 23...Amplifier, 24
...Bidirectional logarithmic element, 25...Resistance, 26...
Logarithmic amplifier (second logarithmic amplifier), 27... adder (
second adder), 28...output terminal (second output terminal). tμ50 Applicant's agent Patent attorney Takehiko Suzue Figure 6

Claims (4)

[Claims] (1) A low-pass rejection filter that receives an input signal from an input terminal, an amplifier that receives an output signal of this low-pass rejection filter, and a bidirectional logarithmic element connected in parallel between the input and output terminals of the amplifier. A logarithmic amplifier made of a resistor, and an adder that adds the output signal of the logarithmic amplifier and the input signal with a predetermined polarity relationship to generate an output signal, and sends the output signal to an output terminal. Characteristic nonlinear amplifier circuit. (2) a low-pass rejection filter; an amplifier that receives the output signal of the low-pass rejection filter; a logarithmic amplifier consisting of a bidirectional logarithmic element and a resistor connected in parallel between the input and output terminals of the amplifier; and an adder that adds the output signal of the amplifier and the input signal from the input terminal with a predetermined polarity relationship to generate an output signal, and sends the output signal to the low-pass removal filter and the output terminal. Characteristic nonlinear amplifier circuit. (3) A first low-pass removal filter that receives the input signal from the first input terminal, an amplifier that receives the output signal of the first low-pass removal filter, and a parallel connection between the input and output terminals of the amplifier. a first logarithmic amplifier comprising a bidirectional logarithmic element and a resistor connected; an output signal of the first logarithmic amplifier and the input signal are added with a predetermined polarity relationship to generate an output signal; a first transmitting signal to a first output terminal;
a first nonlinear adder, and a delay element inserted in a signal path from the first input terminal to the first adder via a first low-pass filter and a first logarithmic amplifier. an amplifier circuit, a second low-pass rejection filter, an amplifier for receiving the output signal of the second low-pass rejection filter, and a bidirectional logarithmic element and a resistor connected in parallel between input and output terminals of the amplifier; an output signal is generated by adding the output signal of the second logarithmic amplifier and the input signal from the second input terminal with a predetermined polarity relationship, and the output signal is added to the second logarithmic amplifier. a second nonlinear amplification circuit having a low-pass removal filter and a second adder having almost the same delay time as the delay element and sending out to a second output terminal, the first and second nonlinear amplification circuits; A non-linear emphasis circuit characterized in that one of the circuits is used as a non-linear emphasis circuit and the other is used as a non-linear de-emphasis circuit.
De-emphasis circuit. (4) The first and second low-pass removal filters share one low-pass removal filter, and the first and second logarithmic amplifiers share one logarithmic amplifier. Nonlinear emphasis/deemphasis circuit.