JPH0122288Y2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field This invention relates to a nonlinear circuit suitable as a γ correction circuit or the like.

Background Art and its Problems For example, in a video camera, it is necessary to perform γ correction on a luminance signal obtained from an image pickup tube. A circuit as shown in FIG. 1 has been considered as a non-linear circuit capable of performing this γ correction.

That is, in FIG. 1, a constant current source _Q2 , (N-K) diodes _D1 , and K diodes _D2 are connected in series between the power supply terminal _T1 and the ground. A constant current signal source Q ₁ is connected to the connection point between D ₁ and D ₂ , and a constant current source Q ₃ is connected in parallel to the diode D ₂ . Further, between the terminal _T1 and the ground, between the collector and emitter of the transistor _Q4 , and (N-J-1) diodes _D3 ,
A constant current source Q ₅ is connected in series, and a transistor Q ₄
The base of is connected to the connection point between constant current source Q ₂ and diode D ₁ . Furthermore, the connection point between diode _D3 and constant current source _Q5 is connected to the base of transistor _Q6 , and between its emitter and ground (J-
1) diodes D ₄ are connected.

Also, at this time, i ₁ : Input signal current of signal source Q ₁ i ₆ : Collector current of transistor Q ₆ (output signal current) I ₂ : Constant current of constant current source Q ₂ I ₃ : Constant current of constant current source Q ₃ Constant current _I5 : Constant current of constant current source _{Q5 Is} : Diodes _D1 to _D4 and transistor _Q4 ,
Saturation current of _Q6 base-emitter diode N, J, K: Integers of 1 or more.

Therefore, if I ₂ = I ₃ ...(i), only the signal current i ₁ flows through the diode D ₂ , and at this time, the terminal voltage of the series circuit of the diodes D ₁ and D ₂ and the transistor Q ₄ , Q ₆ and the terminal voltage of the series circuit of diodes D ₃ and D ₄ are equal, so the following equation is obtained.

(N-K)kT/qlnI ₂ /Is+KkT/qlni ₁ /Is = (N-J)kT/qlnI ₅ /Is+JkT/qlni ₆ /Is ∴(I ₂ /Is) ^NK・(i ₁ /Is) ^K = (I ₅ /Is) ^NJ・(i ₆ /Is)J ∴i ₆ = αi ₁ ^K/J …(ii) α=I ₂ ^NK/J /I ₅ ^NJ/J That is, according to equation (ii) , the circuit shown in FIG. 1 can obtain various γ characteristics by selecting the numbers J and K of the diodes D ₁ to D ₄ .

Moreover, the γ characteristic is not a polygonal line approximation, but a complete curve.

However, in the circuit shown in Figure 1, for equation (ii) to hold, equation (i) I ₂ = I ₃ ...(i) must hold; if equation (i) holds, then When not, equation (ii) becomes i ₆ = α (I ₂ − I ₃ + i ₁ ) ^K/J …(iii), which includes the DC term (I ₂ − I ₃ ), and the complete γ Characteristics become unobtainable.

Moreover, this DC term (I ₂ - _{I 3} ), that is, the difference current (I ₂ - I ₃ ), has a large influence on the characteristics of the rising part (low signal level part) of the γ characteristic, so the current I ₂ , I ₃ must match on the order of pA (picoampere).

However, it is difficult to precisely match the currents I ₂ and I ₃ in this way, and furthermore, when temperature characteristics are taken into consideration, stable operation cannot be expected at all. Also,
Near the rise of the γ characteristic, the diode _D1 and
Since the potential at the connection point with D ₂ drops, it is not easy to draw out the current I ₃ stably.

Furthermore, for example, when approximating a new third γ characteristic by combining the first γ characteristic and the second γ characteristic, the first
If the currents I ₂ , I ₅ in the circuit that form the γ characteristics of and the currents I ₂ , I ₅ of the circuit that forms the second γ characteristics become different in magnitude, the magnitude of the coefficient α in equation (ii) As a result, the third γ characteristic cannot be set to the desired characteristic.

Therefore, as shown in FIG. 2, for example, the differential amplifier 11 and constant current sources Q ₁₄ and Q ₁₅ are used to
A circuit that supplies currents I ₂ and i ₁ to D ₁ and D ₂ has been considered.

That is, in FIG. 2, the transistor
Resistors R _{11 and} R ₁₂ are connected in series between the emitters of Q 11 and Q ₁₂ , and a constant current source Q ₁₃ is connected between the connection midpoint of resistors R ₁₁ and R ₁₂ and a reference potential point, for example, ground. are connected to configure the differential amplifier 11, and the base of the transistor _Q11 is connected to the input terminal _T11 .
For example, a luminance signal of negative synchronization polarity is supplied here.

In addition, the collectors of transistors Q ₁₁ and Q ₁₂ and
Constant current sources Q ₁₄ and Q ₁₅ are connected between the power supply terminal T ₁ and K diodes D ₂ are connected in series between the collectors of the transistors Q _{11 and} Q ₁₂ . (N-K) diodes _D1 are connected in series between the ground and the ground.

Further, a voltage comparison circuit 12 is provided, and its non-inverting input terminal and inverting input terminal are connected to transistors Q ₁₁ ,
are connected to the collectors of _Q12 , respectively, and comparator circuit 1
The output terminal of transistor Q 2 is connected to the base of transistor Q ₁₂ , and a clamping capacitor C ₁₁ is connected between this base and ground. Note that a clamp pulse for performing pedestal clamping of the luminance signal is supplied to the comparison circuit 12 from the terminal _T12 .

Also, the constant current source Q ₅ in Fig. 1 is the transistor Q ₅
and elements Q ₄ to Q ₆ , D ₃ , D ₄
are connected as in FIG. 1, the base of transistor Q ₄ is connected to the collector of transistor Q ₁₂ , the base of transistor Q ₅ is connected to diode D ₁
The current mirror circuit 13 is connected to the connection midpoint of the first and second diodes D ₁ a and D ₁ b from the ground side, and the diode D ₁ a and the transistor Q ₅ constitute a current mirror circuit 13 .

Furthermore, elements similar to elements Q ₄ to Q ₆ , D ₃ , and D ₄
Q ₄₁ to Q ₆₁ , D ₃₁ , and D ₄₁ are connected in the same way, and
At this time, another current mirror circuit 131 is configured by the diode D ₁ a and the transistor Q ₅₁ .

In addition, if I ₁₃ ~ I ₁₅ : constant current of constant current sources Q ₁₃ ~ Q ₁₅ , then
As an example, I ₁₃ = 400 μA I ₁₄ = 200 μA I ₁₅ = 500 μA.

In such a configuration, when a luminance signal is supplied to the terminal T ₁₁ , the signal is transmitted to the loop of the transistor Q ₁₁ ←→transistor Q ₁₂ ←→diode D ₂ ←→transistor Q ₁₁ as shown by the arrow in FIG. current
i ₁ flows. Further, in this case, the collector voltages of transistors Q ₁₁ and Q ₁₂ when the input level of terminal T ₁₁ is 0 (pedestal level) are compared in comparator circuit 12, and the comparison output is clamped, and the voltage of transistor Q ₁₂ is Since it is fed back to the base, the DC levels of the collector voltages of transistors Q ₁₁ and Q ₁₂ are equal to each other, and the diode D ₂
No direct current flows through. i.e. diode
Only the signal current _i1 flows through _D2 . …() Also, if I ₂ is the current flowing through the diode D ₁ , then I ₂ = I ₁₄ − I ₁₅ − I ₁₃ …(iv), and the signal current _{i 1 does} not flow through the diode D 1,
Only a constant current I ₂ flows. ...() Furthermore, a series circuit of diodes D ₁ and D ₂ is connected in parallel between the base of transistor Q ₄ and ground. ...() Therefore, with these terms () to (), the circuit in Figure 2 is equivalent to the circuit in Figure 1, and in particular, with terms (), equation (ii) i ₆ = αi ₁ ^K/J ... (ii) holds true. In other words, the output signal current i ₆ has a γ characteristic relative to the input signal current i ₁ .

Further, if the output signal current (collector current) of the transistor Q ₆₁ is i ₆₁ , the current i ₆₁ also has a γ characteristic with respect to the input signal current i ₁ for the same reason.

Also, at this time, since the current mirror circuits 13 and 131 are constituted by the transistors Q ₅ and Q ₅₁ with the diode D ₁ a on the input side, the collector currents I ₅ and I ₅₁ of the transistors Q ₅ and Q ₅₁ are I ₅ = I ₂ I ₅₁ = I ₂ ...(v). Therefore, formula (ii) becomes i ₆ /I ₂ = (i ₁ /I ₂ ) ^K/J …(vi), and similarly, i ₆₁ /I ₂ = (i ₁ /I ₂ ) ^K/J ₁ ...(vii) J ₁ : Number of diodes D ₄₁ +1. In other words, as shown in Figure 3, the current
i ₆ and i ₆₁ are signal currents of K/J and K/J _squared normalized by current I ₂ .

Therefore, if we combine the currents i ₆ and i ₆₁ as they are, we get
It is possible to approximate an output signal with a new γ characteristic.

In this way, according to the circuit shown in FIG. 2, it is possible to obtain the perfect γ characteristic shown in equation (ii). Furthermore, a new third γ characteristic can be obtained by combining the first and second γ characteristics. Moreover, the features of the circuit shown in FIG. 1 are not lost, and it can be easily integrated into an IC.

However, in the circuit shown in FIG. 2, if the numbers J and K of diodes differ, the temperature characteristics of the output signal current _i6 will differ.

In other words, when formula (vi) is transformed, i ₆ = I ₂ ^1-K/J・i ₁ ^K/J (viii), but here, the currents i ₁ and I ₂ have different temperature characteristics, When the temperature T changes by ΔT, the current i ₁
becomes the size of (1+a)i ₁ from the size of i ₁ ,
Suppose that the current I ₂ changes from the magnitude of I ₂ to the magnitude of (1+b)I ₂ . Then, the output signal current at this time is
i ₆ is calculated from equation (viii) as follows: i ₆ = {(1+b)I ₂ } ^1-K/J {(1+a)i ₁ } ^K/J = (
1+b) ^1-K/J (1+a) ^K/J I ₂ ^1-K/J i ₁ ^K/J …(ix) Therefore, the current i ₆ is equal to the number of diodes J,
If K is different, the temperature characteristics will be different.

The same applies to the current i ₆₁ and i ₆
When ≠i ₆₁ , since J≠J ₁ , the temperature characteristics of the currents i ₆ and i ₆₁ will be different. That is, if a plurality of outputs are extracted, the temperature characteristics of the outputs will be different.

Furthermore, since the temperature characteristics of each output vary in this way, if the third γ characteristic is obtained by synthesis, it will no longer be normalized if there is a temperature change.

Purpose of the invention This invention aims to eliminate these problems.

Summary of the invention Therefore, in this invention, as shown in FIG. 4, for example, the current I ₂ of the diode D ₁ is detected,
This detection output is fed back to the constant current source Q ₁₄ to control the current I ₂ to the reference value Ir.

Example In other words, in the example shown in FIG. 4, there are three diodes _D1 , _D1a to _D1c , and one diode _D2 .
, diode D ₃ is 2, diode D ₄ is 0,
This is the case where there is one diode D ₃₁ and one diode D ₄₁ (N=4, K=1, J=1, J ₁ =2).

Resistors R ₁₀₁ to R ₁₀₃ and diode D ₁₀₁ are connected to the collectors of transistors Q ₁₁ and Q ₁₂ . In this case, elements R ₁₀₁ to R ₁₀₃ and D ₁₀₁ carry the signal current
This is to give a slight offset to i ₁ to reduce the impedance when looking from the input terminal of the comparison circuit 12 to the collector side of the transistors Q ₁₁ and Q ₁₂ , thereby improving frequency characteristics.

Further, the transistors Q ₁₅₁ to _{Q 153} constitute a current mirror circuit 15, and a constant current source Q ₁₅₄ is connected to this to constitute a constant current source Q ₁₅ .

In addition, the transistors Q ₁₄₁ to _{Q 143} constitute a current mirror circuit 14, and the collector of the transistor Q ₁₆₂ is connected to this to form a constant current source.
Q ₁₄ is configured. In this case, the transistor Q ₁₆₂
constitutes the differential amplifier 16 together with the transistor Q ₁₆₁ and the constant current source Q ₁₆₃ . And the transistor Q ₁₆₁ has a bias resistor R ₁₆₁ ,
A constant base bias voltage is provided by _R162 .

Furthermore, the base of transistor Q ₁₇₁ is connected to the connection point between diodes D ₁ a and D ₁ b, and the diode
The connection point between D ₁ b and D ₁ c is connected to the base of transistor Q ₁₇₂ , and the collector and emitter of transistor Q ₁₇₁ are connected between the emitter of transistor Q ₁₇₂ and ground, forming a current mirror circuit. 17 are constructed. This current mirror circuit 17
is a detection circuit that detects the current I ₂ in diode D ₁ and the collector of transistor Q ₁₇₂ is connected to the load resistor
Connected to R ₁₇₁ and to the base of transistor Q ₁₆₂ .

In addition, a transistor Q ₁₈₁ is provided, and a constant current source Q ₁₈₂ is connected to its emitter to operate the transistor.
Q ₁₈₁ is used as an emitter follower, and the collector output of transistor Q ₁₆₂ is negatively fed back to the base of transistor Q ₁₆₂ through transistor Q ₁₈₁ and capacitor F ₁₈₁ to prevent oscillation.

According to such a configuration, the diodes D ₁ a,
Since D ₁ b and the transistors Q ₁₇₁ and Q ₁₇₂ constitute the current mirror circuit 17, if the collector current of the transistor Q ₁₇₂ is I ₁₇ , then I ₁₇ =I ₂ . . . (x).

Further, the collector current I ₁₆ of the transistor Q ₁₆₂ is also the collector current of the transistor Q ₁₄₃ , and since the transistors Q ₁₄₁ to _{Q 143} constitute the current mirror circuit 14, I ₁₄ =I ₁₆ ().

At this time, a constant reference current Ir is flowing through the resistor _R161 , so if the current _I2 increases for some reason, the current will increase according to equation (x).
As I ₁₇ increases and current I ₁₆ decreases, current I ₁₄ decreases according to equation (x), and if current I ₁₄ decreases, then according to equation (iv), I ₂ = I ₁₄ + I ₁₅ − I ₁₃ ... (iv) Therefore, negative feedback is applied such that the current I ₂ decreases, and I ₂ = Ir...().

Since Ir=V _CC /R ₁₆₁ + R ₁₆₂ ...(), from equation (), I ₂ =V _CC /R ₁₆₁ +R ₁₆₂ ...(). That is, the temperature characteristic of the current I ₂ is
This is only due to the temperature characteristics of R ₁₆₁ and R ₁₆₂ .

On the other hand, the signal voltage corresponding to the input signal current i ₁ is v ₁
Then, i ₁ = v ₁ / R ₁₁ + R ₁₂ ...(), and _the temperature characteristics of _the signal current i ₁ are also
This is due only to the temperature characteristics of

Since the temperature characteristics of the resistors R ₁₆₁ , R ₁₆₂ , R ₁₁ , and R ₁₂ can be made equal, especially when integrated into an IC,
Since they can be easily made equal, the temperature characteristics of the currents i ₁ and I ₂ can be made equal, and in equation (ix), a=b...(). Therefore, formula (ix) is: i ₆ = (1+b) ^1-K/J (1+a) ^K/J I ₂ ^1-K/J i ₁ ^K/J …() = (1+a) ^1-K/J (1+a) ^K/J I ₂ ^1-K/J i ₁ ^K/J = (1+a) I ₂ ^K/J i ₁ ^K/J …(). That is, the temperature characteristics of the output signal current i ₆ are not affected by the numbers J and K of diodes (the temperature characteristics are the same as those of the input signal current i ₁ ).

The same applies to the output signal current source _i61 .

Thus, according to this invention, it is possible to obtain a γ characteristic of temperature characteristics that is not affected by the number J and K of diodes. Further, since it is not affected by the number J and K of diodes, even if a plurality of γ characteristics are obtained, they can be made to have the same temperature characteristics. Furthermore, since the temperature characteristics of each γ characteristic are the same, when the third γ characteristic is synthesized, it can be normalized.

Effects of the invention It is possible to obtain a temperature characteristic γ characteristic that is not affected by the number J and K of diodes. Further, since it is not affected by the number J and K of diodes, even if a plurality of γ characteristics are obtained, they can be made to have the same temperature characteristics. Furthermore, since the temperature characteristics of each γ characteristic are the same, the third γ
When properties are combined, they can be normalized.

[Brief explanation of drawings]

1 to 3 are diagrams for explaining this invention, and FIG. 4 is a connection diagram of an example of this invention. 12 is a voltage comparison circuit.

Claims (1)

[Scope of utility model registration request] The emitters of the first and second transistors are
are commonly connected to a constant current source to form a differential amplifier, and second and third constant current sources are connected to the collectors of the first and second transistors, and the collectors of the first transistor and and a reference potential point, (N-K) first diodes are connected in series, K second diodes are connected in series between the collectors of the first and second transistors, and the The base of a third transistor is connected to the collector of the second transistor, and (N-J-1) third diodes are connected between the emitter of the third transistor and the reference potential point;
Between the base and emitter of the fourth transistor,
(J-1) fourth diodes are connected in series, a fourth constant current source is connected to the base of the fourth transistor, and an input signal is supplied to the base of the first transistor. An output signal with non-linear characteristics using the N, J, and K as parameters is taken out to the collector of the fourth transistor, and a current flowing through the first diode is detected, and this detection output is used as the output signal of the first to third transistors. A non-linear circuit in which the current flowing through the first diode is fed back to one of the constant current sources so that it becomes a reference value. However, the above N, J, and K are integers of 1 or more.