DE1158552B - Non-linear circuit, especially for correcting the gamma error in television sets - Google Patents

Description

Circuits for gamma correction are used in televisions primarily to compensate for the non-linear relationship between the reproduced brightness of a picture display tube and that on the tube to correct the applied modulation voltage. In order to achieve a correction, a circuit for Gamma correction must be such that the output voltage depends on the input voltage runs according to a certain non-linear law.

The present invention shows such a non-linear circuit, which is particularly used for correction of gamma errors in televisions.

The invention consists in that the circuit contains a series circuit consisting of the collector resistance, the collector-emitter path of a transistor and the emitter resistance of this transistor consists that the input voltage to the two ends of this series circuit and at the same time to the Input of the transistor is applied such that the current in the transistor is a non-linear function of the is the instantaneous input voltage, and that the output voltage at part of the series circuit is tapped.

For a better understanding, the invention is explained in more detail below with reference to the drawing.

Fig. 1 shows an embodiment of the non-linear circuit according to the invention for correcting the Gamma error;

FIG. 2 shows the relationship between the collector current of the transistor of FIG. 1 and the the circuit applied voltage;

FIG. 3 shows a further graphic illustration which is used to explain the function of the circuit serves.

The non-linear circuit in Fig. 1 essentially comprises a non-linear attenuator, consisting from the series connection of a linear resistor 1 and the collector-emitter path of a transistor 2. In the emitter line of the transistor 2 there is a negative feedback resistor 3, the lies both in the input circuit and in the output circuit of the transistor 2. The one with the attenuator The voltage to be changed is applied to the circuit via input terminals 4, 5. The non-linearly changed voltage is applied across the series circuit of the collector-emitter path of the transistor 2 and the emitter resistor 3 at the output terminals 6, 7 removed. There is a fixed resistor 8 in between the input terminals 4, 5 Row switched on with a potentiometer 9. The variable tap on the potentiometer 9 is with the Base of transistor 2 connected.

Non-linear circuit,

especially for correction

of the gamma error in televisions

Applicant:

Electric & Musical Industries Limited,
Hayes, Middlesex (Great Britain)

Representative: Dr.-Ing. B. Johannesson, patent attorney,
Hanover, Göttinger Chaussee 76

Claimed priority:
Great Britain, March 10, 1961 (No. 8758)

Savior Lawrence Cachia, Kalkara (Malta),
has been named as the inventor

It can be shown that, if a transistor works in the vicinity of its current start point, the collector current I _{c runs} as a function of the voltage Φ across the base-emitter path according to the following law:

h = / ksat) * [exp

in this equation means:

/ (so «) = base-emitter saturation current,

q = electron charge,

K - Boltzmann's constant,

T = absolute temperature in Kelving degrees,

γ '- current amplification factor,

I _co = residual collector current.

In the above equation, the term with I _co is generally small.

In the expression Φ = k · Vi _n -Ic · Re , k is the damping factor of the series connection of resistor 8 with potentiometer 9, Vi _{n is} the input voltage applied between terminals 4, 5 and R _{e is} the resistance value of resistor 3. The collector current runs therefore as a function of the input voltage Vi _n according to curve 10 in Fig. 2. The negative feedback resistor 3 is used in the circuit to define the range for the input voltage Vi _n in which the collector current has an exponential

309 767/172

Claims (3)

3 4 barrel has to enlarge. Hence the tension
at the collector load resistance 1 an exponential
History and opposite sense as the first non-linear circuit, particularly the input voltage ^. "For example, assume correction of the gamma error in television sets, that the input voltage V in _in accordance with curve 11 in 5, characterized in that it comprises a series Fig. 3 is linear over time. Then the circuit runs contains, which consists of the collector resistance voltage at the collector load resistor 1, which was equal to (1), the collector-emitter path of a trandem product of the collector current I _c and the sistor (2) and the emitter resistor (3) of this Resistance value R _{c of} the resistance test is, according to the transistor, that the input voltage of the curve 12 in Fig. 3. The subtraction of the two io (V _in ) at the two ends of this series connection, voltages 11, 12, results in a voltage V ₀ according to curve 13 in FIG. 3 at the output terminals and also at the input of transistor (2) 6, 7. is applied in such a way that the current (10) in this voltage is produced by the subtraction of a transistor (2), a non-linear function of the exponential voltage and a linear instantaneous input voltage (F _iK ), and the current voltage. The desired gamma 15 that the output voltage (F ₀ ) at a partial value can be adjusted with the 9 potentiometer. the series connection is tapped. In one embodiment of the invention. 2. Non-linear circuit according to claim 1, According to the circuit, the transistor 2 is of the type characterized in that the base of the Tran-2 N 502. The resistors and the potentiometer sistor (2) directly with the tap of a Potentiohaben doing the following values: 20 meters (9) connected, the parallel to the series resistor 1 2700 Ω circuit (1, 2, 3) and that the output _ Voltage between the collector of the Tran resistor 3 220 U _{sistor (2) and the} resistor 8 4700 Ω away from the transistor (2) at the end of the emitter resistor (3) Potentiometer 9 500 Ω 25 will. 1 sheet of drawings © 309 767/172 11.63