JP2619858B2 - Function approximation function generator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in the following order.

A Field of application in industry B Outline of the invention C Conventional technology (Figs. 11 and 12) D Problems to be solved by the invention (Figs. 12 and 13) E Means for solving problems (FIG. 1) F function (FIG. 1) G embodiment (FIGS. 1 to 10) (G1) Input voltage signal-transconductance characteristic of differential amplifier circuit (FIGS. 2 and 3) (G2) (1) First embodiment (FIGS. 1 and 4) (G3) Second embodiment (FIG. 5) (G4) Third embodiment (FIGS. 6 and 7) (G5) Fourth embodiment ( (FIG. 8) (G6) Other Embodiments (FIGS. 9 and 10) Effects of the Invention A Industrial Field of the Invention The present invention relates to a function approximation function generator, for example, a gamma correction circuit in a television camera. It can be applied to

B. Summary of the Invention The present invention relates to a linear approximation type function generating circuit, in which a common input voltage signal is provided in parallel to a plurality of differential amplifier circuits having different transconductance characteristics with respect to an input voltage signal, and the plurality of differential amplifier circuits are By amplifying an input voltage signal to at least one of them and providing an output voltage signal by connecting a common load, various input / output characteristics including an input / output characteristic having a high gain portion can be obtained. It can be realized and can be easily adapted to an integrated circuit.

C. Prior Art A television camera is provided with a gamma correction circuit for transmitting an output voltage signal having a level substantially in accordance with a logarithmic function according to an input voltage signal so as to obtain linearity of the entire system. Conventional gamma correction circuit
There is one shown in FIG.

The gamma correction circuit is connected via the emitter series resistor R _E11 and R _E12 having respective emitter terminals of the two NPN-type transistors Q1 and Q2 same resistance value R _E12, the resistors
The constant current source 1 is connected between the connection center A of R _E11 and R _E12 and the earth line L1, the collector terminal of the transistor Q1 is connected to the power line L2, and the collector terminal of the transistor Q2 is connected via the load resistance _RL . the differential amplifier circuit 5 formed by connecting the power supply line L2 Te comprises, an input voltage signal v _in to the base terminals of both transistors Q1 and Q2 are made as given.

A connection point B between the crater terminal of the transistor Q2 and the load resistor _RL is connected to an output terminal via an output line L3. Further, between the output line L3 and the earth line L1, for example, a resistor R1, a diode D1 A series circuit 2 composed of a DC power supply V1, a series circuit 3 composed of a resistor R2, a diode D2 and a DC power supply V2, and a series circuit 4 composed of a resistor R3, a diode D3 and a DC power supply V3 are connected in parallel. Here, each of the DC power supplies V1, V2, V3 is selected in a relation of V1 <V2 <V3.

In a gamma correction circuit having such a configuration,
When the input voltage signal v _in the value smaller than the voltage v1 shown in Figure 12 is obtained, low potential obtained at the connection midpoint B, current since any diode D1~D3 series circuit 2-4 also not turned on flows Instead, the output signal v _out by the gain R _L / R _E is output as it is.

Input voltage signal v _in is larger than the value v1, the potential of the input voltage signal v _in is obtained is amplified by the connection point B is increased beyond the forward voltage VF of the diode from the DC power supply V1, the series circuit 2 Electric current flows. At this time, since the load resistance _RL and the resistance R1 are connected in parallel, the output voltage by the gain _RL R1 / R _E ( _RL R1 is a combined resistance value of the resistance _RL and the resistance R1) is obtained. The signal v _out is output.

Similarly, the input voltage signal v _in is changed to the value v shown in FIG.
If it is larger than 2, a current flows through the series circuits 2 and 3,
Gain R _L R1R2 / R output voltage signal v _out by _E is output, further input voltage signal v _in is greater than the value v3,
A current flows through all the series circuits 2 to 4 and the gain _RL R1R2
R3 / R _E by the output voltage output v _out is output.

Thus, as shown in FIG. 12, the output voltage signal v _in response to the input voltage signal vin whose slope gradually becomes gentler.
_Out desired characteristics (hereinafter referred to as input / output characteristics) CH are obtained.

Problems E to be Solved by the Invention Meanwhile, when we consider only the differential amplifier circuit 5 in such a conventional circuit, an input voltage signal v _in the incoming first
The output voltage signal amplified by the gain R _L / R _E is transmitted as indicated by the imaginary line F in FIGS. 2 and 13. Therefore, as shown in FIG. 13, the conventional circuit basically exceeds the actual dynamic range DRR of the output voltage signal v _out by basically multiplying the entire range of the input voltage signal v _in by R _L / R _E. Requires range DRP.
The maximum value of such a basic dynamic range DRP is suppressed by the power supply voltage. Therefore, as shown in FIG. 13, when the power supply voltage V _CCH is high, a high gain portion RH (corresponding to the slope) is obtained. However, it is difficult to obtain a high gain as the gain of the high gain section RL when the power supply voltage V _CCL is low. That is, when driven by a low power supply voltage, there is a possibility that desired input / output characteristics cannot be realized.

Further, in the conventional circuit, the gain is changed by sequentially turning on the plurality of serial circuits 2 to 4, so that only a gradually changing method can be obtained. For example, to reduce the low-level gain of the input voltage signal v _in order noisy near the black level in the video signal, then want the input and output characteristics of changing the gain logarithmically so as to correct the linearity However, the conventional circuit cannot change the gain from a small gain to a large gain, and cannot realize such input / output characteristics. That is, it can be said that the range of the degree of freedom of the input / output characteristics obtained by the conventional circuit is narrow.

Furthermore, according to the conventional circuit, it is difficult to obtain a differential output because the series circuits 2 to 4 are provided.
Therefore, the circuit configuration of the next stage cannot be operated by differential output, and the design of an integrated circuit (IC) that often uses a large number of differential amplifier circuits is limited from that point. Become.

The present invention has been made in consideration of the above points, and can realize a high gain even at a low power supply voltage, and is particularly effective when it is mounted on an IC capable of obtaining various input / output characteristics. It is intended to provide a function generation circuit.

In the present invention for solving means above problems to solve E problems, common input voltage in parallel to the plurality of differential amplifier circuits 71 to 73 properties of the mutual conductance gm is different with respect to the input voltage signal v _in together provide a signal v _in, it provides an input voltage signal further amplifies the input voltage signal v _in to the at least one differential amplifier circuit (e.g., 73) of the plurality of differential amplifier circuits 71 to 73, a plurality of differential amplifier A common load RL1 is connected to the circuits 71 to 73 to derive an output voltage signal v _out to an output terminal, and the input voltage signal v _in
The characteristic of the output voltage signal v _{out with} respect to is bent at at least one or more predetermined levels of the input voltage signal v _in .

By F acting the differential amplifier circuit 71, 72 and 73 to the input voltage signal obtained by amplifying the input voltage signal v _in or input voltage signal v _in is given, amplifies this input voltage signal v _in or input voltage signal v _in And the transconductance g _m1 , g _m2 ,
collector current according to g _m3 (in the fourth embodiment, i _o1 , i _o2 , i
_o3 ) _Flow . Here, since the load RL1 is commonly connected to each of the differential amplifier circuits 71, 72, and 73, a current iL of the sum of the respective collector currents flows through the load RL1. Accordingly, iL flowing through the load RL1 is the sum of the respective transconductances g _m1 and g _m2 and the substantial transconductance g _m3 × G of the differential amplifier circuit 73 to which the amplified input voltage signal is supplied, that is, the total transconductance g _m1 + _gm2 + _gm3 × G according to the output voltage signal v
_out also depends on the total transconductance.

Therefore, the total transconductance g _m1 + g _m2 + g _m3 × G
Input but with selected characteristics of the transconductance g _m1, g _m2, g _m3 to appropriately change to the input voltage signal v _in to the input voltage signal v _in each differential amplifier circuit 71 to 73, which is amplified by selecting the differential amplifier circuit to which the voltage signal is input, it is possible to obtain characteristics of the desired output voltage signal v _out with respect to the input voltage signal v _in.

G Examples Hereinafter, some examples of the present invention will be described with reference to the drawings.

(G1) Input Voltage Signal-Transconductance Characteristics of Differential Amplifier Circuit First, prior to the description of each embodiment, the characteristics of the mutual conductance of the differential amplifier circuit with respect to the input voltage signal will be described. As shown in Figure 2, is connected emitter terminals of the first and second NPN type transistors Q3 and Q4 via the emitter series resistor R _e1 and R _e2 have the same resistance ground R _e12, the resistors R _e1 and Constant current I between the connection point C of R _e2 and ground
Of the differential amplifier circuit 7 configured by connecting the constant current source 6 for attracting the input current when the incoming input voltage signal v _in (hereinafter, the case where the input voltage signal is not biased is indicated by the same reference numeral) changes. The rate of change of the collector current (output current) i _c4 of the transistor Q4, ie, the transconductance g
_m can be approximately expressed by the following equation.

| v _in | <V ₀ = R _e I / 2… (1) | v _in |> V ₀ = R _e I / 2… (3) This input voltage signal v _in is equal to or higher than a predetermined value (V _0), a constant current I to be sucked by the constant current source 6 flows through only the first transistors Q3, also the input voltage signal v _in is a predetermined value (- V ₀ ) or less, the constant current I
Q4 only flow, even when the input voltage signal v _in is changed the output current i
_c4 does not change, whereas, in that the input voltage output v _in is when the value of the predetermined range -V ₀ ~V ₀ output current i _c4 is that changes substantially in proportion to the input voltage signal v _in Based.

Such an input voltage signal v _in and transconductance g _m
The characteristic between the two changes in the form of a rectangular wave REC as shown in FIG.

Here transconductance g _m of the characteristics (hereinafter, v _in -g _m is referred to as characteristic) with respect to the input voltage signal v _in the differential amplifier circuit 7 as described above (1) to (4) emitter series As is evident formula Various types can be obtained by appropriately selecting the resistance _Re and the constant current I.

(G2) First Reference Example Hereinafter, a first reference example will be described with reference to the drawings. In FIG. 1, three sets of differential amplifier circuits 71, 72, and 73 having a configuration similar to that shown in FIG. 2 are connected in parallel. That is, the first transistor Q3 of each differential amplifier circuit 71, 72, 73
1, the collector terminals of Q32 and Q33 are respectively connected to the power supply line L2, and the collector terminals of the second transistors Q41, Q42 and Q43 of the respective differential amplifier circuits 71, 72 and 73 are connected to the output line L3, respectively. both transistors Q31 and Q41, Q32 and Q42, Q33 and the respective input voltage signal v _in to the base terminal of Q43 have been made as given in the differential amplifier circuit 71, 72, 73. A load resistance RL1 is connected between the power supply line L2 and the output line L3, and an output voltage signal v _out (hereinafter, the case where a bias component is removed is indicated by the same reference numeral) from both ends of the load resistance RL1. It is sent out.

In the above configuration, first, second, by the third differential amplifier circuit 71, 72, 73 to obtain et supplied with an input voltage signal v _in, the following expressions _{i 01 = v in · g m1} ... ( _{5) i 02 = v in ·} g m2 ... (6) i 03 = v in · g m3 ... output signal i ₀₁ in accordance with _{(7), i 02, i} 03 flows. Where g _m1 ,
g _m2 and g _m3 are the mutual conductances of the differential amplifier circuits 71, 72 and 73, respectively. These (5) can be from - (7), represented by load resistors RL1 to the following equation _{iL = i 01 + i 02 +} i 03 = v in · the current iL flowing through _{(g m1 + g m2 + g} m3) ... (8) . Accordance connexion, the output signal v _out can be expressed by the following formula _{v out = RL1 · iL = v} in · RL1 · (g m1 + g m2 + g m3) ... (9).

As is apparent from equation (9), the gain in this embodiment is determined by the product of the load resistance RL1 and the total mutual conductance Σg _m (= g _m1 + g _m2 + g _m3 ) of the three differential amplifier circuits 71 to 73. Since the load resistance RL1 is a constant value, the gain is proportional to the total transconductance Σg _m .

Accordance connexion, it is possible to obtain a desired input-output characteristic by suitably selecting the overall transconductance Shigumag _m with respect to the input voltage signal v _in accordance with this embodiment.

For example, a first differential amplifier circuit 71 v _in -g _m characteristic R
EC1 fourth view parameters so that only have a conductance g _m1 value 1 / R ₁ in the range -V ₀₁ ~V ₀₁ as shown in (A) R ₁ (the value of the resistor R31, R41), the I ₁ select a value, also, for the second differential amplifier circuit 72 v _in -g _m characteristic REC2 of the first differential amplifier circuit 71 v _in -g _m characteristic REC1 than non-zero conductance value 1 / R ₂ wide range -V ₀₂ ~V ₀₂ can take the value 1 / R ₂ is such that each parameter R ₂ small conductance g _{m @ 2} of the range (the value of the resistor R32, R42), selects the value of I ₂ , And also the third differential amplifier circuit 73, v _in -g _m
Each parameter R ₃ (resistors R33, R3) is set so that the range −V _{03 to} V ₀₃ which can take a conductance value 1 / R ₃ other than zero from the characteristic REC2 is wide, and the value 1 / R ₃ of the conductance _m3 in that range is small.
43 value of), and was selected value of I _3.

In this case, the overall transconductance Shigumag _m, as shown in FIG. 4 (B), the input voltage signal v _in is 0 -V ₀₃ smaller ranges, -V ₀₃ in the range of _{~-V 02 1 / R 3} , −V ₀₂ to −V ₀₁
In the range of _{1 / R 2 + 1 / R} 3, in the range of _{-V 01 ~V 01 1 / R 1} + 1 / R 2 +
In the range of 1 / R _3, V ₀₁ ~V in the range of _{02 1 / R 2 + 1 /} R 3, V 02 ~V 03
1 / R _3, V ₀₃ and stepwise increased as 0 in a range greater than exhibits then the characteristic CH2 as symmetrically stepwise reduced.

Accordance connexion, as input-output characteristic of this case is shown in FIG. 4 (C), the gain is maximum when the range input voltage signal v _in is -V ₀₁ ~V _01, the gain in accordance smaller than this range, It exhibits a point-symmetric so-called S-shaped characteristic S in which the gain gradually decreases, and conversely, as the gain becomes larger than this range, the gain gradually decreases. In other words, it is possible to obtain a characteristic different from the input / output characteristic in which the gain gradually decreases as the input voltage signal vin increases as _in the conventional circuit.

In practice, when the desired input / output characteristics as shown in FIG. 4 (C) are determined, the total transconductance Σg _m
Is determined, and finally the number of the differential amplifier circuits and each parameter are determined, thus achieving desired input / output characteristics.

According to the first reference example, the required dynamic range is unchanged range of the output voltage signal v _out, it is larger than the range of the output voltage signal v _out as in the conventional circuit, and maximum range of the input voltage signal There is no range of the product of the gain and the dynamic range can be greatly improved compared to the conventional circuit, and the gain of the high gain section is not restricted even if a low power supply voltage is used. .

(G3) Second Reference Example Next, a second reference example of the present invention will be described with reference to FIG. 5 in which parts corresponding to those in FIG.

In the second reference example, each differential amplifier circuit 71, 72,
The collector terminals of the first transistors Q31, Q32, and Q33 are connected to a second output line L4, and a second load resistor RL2 is connected between the output line L4 and the power supply line L2.

In the above configuration, the operation in which the output voltage signal v _out to the first output line L3 is obtained is similar to the operation of the first reference example shown in Figure 1. Since the differential amplifier circuits 71, 72, and 73 are configured, the collector currents i _c31 , i _c32 , and i _c33 of the first transistors Q31, Q32, and Q33 are _equal to the second transistors Q41, Q4, respectively.
2. The current changes inversely with respect to the collector currents i ₀₁ , i ₀₂ and i _{03 of} Q43. Therefore, the current iL2 flowing through the second load resistor RL2 is
Changes in reverse with respect to the current iL flowing through the load resistance RL1.

Thus, the second output line L4 output voltage signal of opposite phase ▲ ▼ is obtained for the output voltage signal v _out obtained to the first output line L3.

That is, according to this embodiment, in addition to the same effects as those of the first embodiment, the positive and negative phase output voltage signals vout and ▲
▼ can be obtained, and therefore, there is an effect that it can be easily applied to an IC in which many circuits operated by differential input signals are mounted.

(G4) Third Reference Example A third reference example of the present invention will be described with reference to FIG.

In the third reference example, each differential amplifier circuit 71, 72,
It is to give to offset the input voltage signal v _in the respective DC power source V _21, V _22, V ₂₃ with respect to 73.
In this way, the input voltage signal v is offset by different amounts.
_{When in} is given to each differential amplifier circuit 71, 72, 73,
As the total transconductance Σg _m , not only a line symmetrical one as shown in FIG. 4 (B) but also various other ones can be obtained, and thus the input / output characteristics are more diverse than those of the circuit of FIG. Thus, a circuit that can form a simple circuit can be obtained.

For example, when offset by the DC power source V _21, V _22, V ₂₃ is no v _in -g _m characteristic properties as shown in FIG. 4 described above (A) REC1, REC2, the differential amplifier circuit having a REC3 71,
As shown in FIG. 7 (A) with respect to 72 and 73, the offset amount ΔV1 (=
Gives V _21), the differential amplifier circuit 72 and the offset amount to zero (= V _22), and providing a small offset amount ΔV3 (= V ₂₃₎ on the negative side for the differential amplifier circuit 73.

In this case, the overall transconductance Shigumag _m, as shown in Figure No. 7 (B), the input voltage signal v _in the central value 0 asymmetric with respect to the, and shape values change complicated large or small summer or summer CH3 the exhibits, input-output characteristic exhibits a shape CH4 varied to or finer or larger by range, less of FIG. 7 (C) an input voltage signal to tilt as shown in v _in.

Therefore, according to this embodiment, the dynamic range can be improved in the same manner as in the first embodiment, and in addition to this, not only the S-shaped characteristic as in the first embodiment but also various input / output characteristics can be realized. be able to.

(G5) Fourth Embodiment Next, a fourth embodiment of the present invention will be described with reference to FIG. 8, in which parts corresponding to those in FIG.

In the fourth embodiment, a portion of the differential amplifier circuit, for example for the differential amplifier circuit 73 so as to enter after amplifying via the amplifier circuit 8 before the input voltage signal v _in. In this way, not the preamplifier circuit 8 and the differential amplifying circuit 73 but the circuit part is a transconductance, the gain G of the preamplifier circuit 8 and the transconductance g of the differential amplifying circuit 73.
is equivalent to a differential amplifier circuit having a value of the product G × g _m3 and _m3, performs accordance connexion, operations similar to those of the first embodiment.

According to this embodiment, a differential amplifier circuit having a very large value as a mutual conductance can be equivalently obtained by interposing the amplifier circuit 8, and the input / output characteristics having a very high gain section can be obtained. It can be easily realized.

(G6) Other Embodiments In the above embodiment, three differential amplifier circuits are connected in parallel. However, the present invention is not limited to this, and desired input / output characteristics can be obtained. A plurality of differential amplifier circuits may be connected in parallel as needed.

In the above description, FIG. 4 (A) and FIG. 7 (A)
As shown in FIG. 9, differential amplifier circuits having different input dynamic ranges are connected in parallel, but a differential amplifier circuit having the same input dynamic range is connected to a predetermined value ΔV as shown in FIG. However, it may be used by shifting them relatively. In short, it is only necessary to connect differential amplifier circuits having different v _in -g _m characteristics in parallel to obtain desired input / output characteristics.

Further, the reference example of FIG. 6 is for offsetting an input voltage signal by a DC power supply and applied to a differential amplifier circuit, and the embodiment of FIG. 8 is for differentially inputting the input voltage signal via a separate amplifier circuit. Although those given to the amplifier circuit, combining these characteristic points, it is possible to form a differential amplifier circuit further diverse v _in -g _m characteristic equivalently, as a result, to obtain a variety of input and output Will be able to do it.

For example, when such a function generating circuit is formed, the maximum value O _MAX of the output voltage signal v _out is set to, for example, a power supply voltage of 5 [V].
V _CC and the minimum value O _MIN of the output voltage signal v _{out is} , for example, 2 which is necessary for the constant current source of the differential amplifier circuit to operate normally.
By setting it to [V], the widest dynamic range can be realized. Accordance connexion was compatible with on correspondence (FIG. 10 (A) to the maximum value O _MAX of the maximum value I _MAX output voltage signal v _out of the input voltage signal v _in, as shown in FIG. 10 (A) called the point as an end point MAX), minimum value O _MIN in correspondence of the minimum value I _MIN output voltage signal v _out of the input voltage signal v _in (FIG. 10 (a)
If the above associated point is called the starting point MIN), the maximum dynamic range can be realized.

At this time, as described above, when the offset and the preamplification are appropriately combined, as shown in FIG.
MIN and end point MAX are determined, route RO1 to reach
If RON increases monotonically, a variety of good input / output characteristics can be obtained.

However, the conventional circuit has a starting point MIN as shown in FIG. 10 (B).
The circuit with its versatility for obtaining output characteristics by connecting a straight line従Gai slope decreases further to the input voltage signal linearly LIN than the slope is small v _in increases connecting the end point MAX invention It has to be much smaller in comparison.

In the above description, the collector terminal of each transistor in each differential amplifier circuit in which the in-phase creature current flows to the output line is shown, but some differential amplifier circuits are connected to the same output line. Transistors in which collector currents of opposite phases flow may be connected. In this case, not only the input / output characteristics that monotonically increase (or monotonically decrease) but also the input / output characteristics that change more variously can be obtained. .

Furthermore, the broken line approximation type function generation circuit according to the present invention can be applied not only to the above-described gamma correction circuit in the television camera but also to various circuits as necessary.

H Effects of the Invention As described above, according to the present invention, by providing an amplified input voltage signal to at least one differential amplifier circuit among a plurality of differential amplifier circuits to which a common input voltage signal is applied in parallel. It is possible to obtain a differential amplifier circuit having a transconductance of a very large value equivalent to an input / output characteristic having a very high gain section even at a low power supply voltage. It is possible to obtain a function approximation function generation circuit that can easily form an IC that can form various types of circuits as compared with conventional circuits.

[Brief description of the drawings]

Figure 1 is connection diagram showing a first reference example of the polygonal line approximation function generating circuit, FIGS. 2 and 3 are schematic diagrams illustrating the v _in -g _m characteristic of the differential amplifier circuit, Figure 4 Is a schematic diagram showing various characteristics of the first reference example, FIGS. 5 and 6 are connection diagrams showing second and third reference examples, respectively, and FIG. 7 is a schematic line showing various characteristics of the third reference example. FIG. 8, FIG. 8 is a connection diagram showing an embodiment of a broken line approximation type function generating circuit according to the present invention, FIG. 9 is a schematic diagram for explaining a differential amplifier circuit applicable to the present invention, and FIG. Schematic diagram for explaining the variety of input / output characteristics according to the invention, FIG.
FIG. 11 is a connection diagram showing a conventional circuit, FIG. 12 is a schematic diagram showing input / output characteristics thereof, and FIG. 13 is a schematic diagram for explaining a defect of the conventional circuit. 71-73 ...... differential amplifier circuit, RL1 ...... load resistor, v _in ...... input voltage signal.

Claims (1)

(57) [Claims] 1. A plurality of differential amplifier circuits having mutually different transconductance characteristics with respect to an input voltage signal and amplifying the input voltage signal in parallel, and commonly connected to output terminals of the plurality of differential amplifier circuits. A load for deriving a combined output of the plurality of outputs to an output terminal; and a preamplifier circuit inserted on an input end side of at least one of the plurality of differential amplifier circuits, A bent-line approximation type function generating circuit, wherein an output voltage signal having a characteristic of bending at at least one or more predetermined levels of the input voltage signal is output from the output terminal.