JPH056391B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application 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 Since the terminal voltages between the base and emitter of ₄ and Q ⁶ and the series circuit of diodes D ₃ and D ₄ are equal, 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) 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. In addition, equation (ii) does not include a term for temperature T, and has excellent temperature characteristics.

However, in the circuit shown in Figure 1, in order for formula (ii) to hold, formula (i) I ₂ = I ₃ ...(i) must hold, and if formula (i) holds If not, equation (ii) becomes i ₆ = α (I ₂ − I ₃ + i ₁ ) ^K/J 〓 ……〓 and includes the DC term (I ₂ − I ₃ ), and is completely It becomes impossible to obtain the γ characteristic.

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.

OBJECT OF THE INVENTION The present invention aims to provide a non-linear circuit that eliminates the above-mentioned problems.

Summary of the Invention For this reason, in the present invention, for example, as shown in FIG.
Currents I ₂ and i ₁ are supplied to diodes D ₁ and D ₂ by Q ₁₄ and Q ₁₅ .

Example In other words, in FIG.
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 pace 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 pace 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 ~ R ₆₁ , D ₃₁ , 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 = 200 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 In other words, negative feedback is applied so that the voltage between the positive and negative input terminals of the comparator circuit 12 is 0 volts, so the DC levels of the collector voltages of the transistors Q ₁₁ and Q ₁₂ are equal to each other. Therefore, no direct current flows through diode _D2 . That is, only the signal current _i1 flows through the diode _D2 . ……
() Also, if I ₂ is the current flowing through the diode D ₁ , then I ₁₃ = I ₁₅ + I ₁₄ − I ₂ , so I ₂ = I ₁₄ + I ₁₅ − I ₁₃ ...(iv), and the current flowing through the diode D ₁ The signal current i ₁ does not flow,
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 (), formula (ii) i ₆ = αi ₁ ^K/J ...(ii) holds true. In other words, the output signal current i ₆ is the input signal current i ₁ given a γ characteristic.

Furthermore, 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, the current mirror circuits 13 and 13 are connected by the diode D ₁ a and the transistors Q ₅ and Q ₅₁ .
1, so the transistors Q ₅ and Q ₅₁
The collector currents I ₅ and I ₅₁ of 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/J1 ...(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 present invention, complete γ retention shown in formula (ii) can be obtained. Furthermore, a new third γ characteristic can be obtained by combining the first and second γ characteristics. Furthermore, the characteristics of the circuit shown in FIG. 1 are not impaired, and it can be easily integrated into an IC.

In the example shown in FIG. 4, output signals of the first power, 1/2 power, and 1/4 power are obtained with respect to the input signal current.

That is, in this example, N=4 K=3 J=1 J ₁ =2 and elements similar to elements Q ₄ to Q ₆ and D ₃
Q ₄₂ to Q ₆₂ and D ₃₂ are similarly connected. Further, the number of diodes D ₄₂ +1=J ₂ is set as J ₂ =1. Note that the resistors R ₁₃ and R ₁₄ and the diode D ₁₁ are used to offset the signal current i ₁ , and the resistor R ₁₅ is used to improve the frequency characteristic of the rising portion of the γ characteristic.

Therefore, the collector currents of transistors Q ₆ , Q ₆₁ , and Q ₆₂ have characteristics of 1st power, 1/2 power, and 1/4 power.

In addition, in the above, the diode _D2 is supplied with a DC current that is sufficiently smaller than the signal current _i1 , for example, several
It is also possible to improve the frequency characteristics of the rising portion of the γ characteristics by passing a pA of direct current.

Effect of the invention Output current i ₆ shown by equation (ii) for signal current i ₁
can be obtained. Also, when obtaining multiple output currents, it can be normalized.

[Brief explanation of the drawing]

1 and 3 are diagrams for explaining this invention, and FIGS. 2 and 4 are connection diagrams of an example of this invention. 12 is a voltage comparison circuit.

Claims (1)

[Claims] 1 The emitters of the first and second transistors are commonly connected to a first constant current source to configure a differential amplifier, and the collectors of the first and second transistors are connected to second and third constant current sources. A current source is connected, (NK) first diodes are connected in series between the collector of the first transistor and a reference potential point, and a current source is connected between the collectors of the first and second transistors. A comparison circuit is provided in which K second diodes are connected in series, the collector voltages of the first and second transistors are compared, and a comparison output is fed back to the base of the second transistor;
The base of a third transistor is connected to the collector of the second transistor, and the emitter of the third transistor is connected to the reference potential point (N
- J-I) third diodes are connected in series between the base and emitter of the fourth transistor, and (J-I) fourth diodes are connected in series;
A fourth constant current source is connected to the base of the transistor, an input signal is supplied to the base of the first transistor, and the collector of the fourth transistor has nonlinear characteristics with N, J, and K as parameters. A nonlinear circuit from which the output signal of is taken. However, the above N, J, and K are integers of 1 or more.