JP3285152B2 - Video signal amplifier circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[Table of Contents] The present invention will be described in the following order. Industrial Application Conventional Technology (FIG. 4) Problems to be Solved by the Invention Means for Solving the Problems Actions Embodiment (1) First Embodiment (2) Second Embodiment (3) Other Example Effect of the Invention

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal amplifying circuit, and more particularly, to a video signal amplifying circuit suitable for use in a preamplifier.

[0003]

2. Description of the Related Art Conventionally, in a television receiver,
Extracting luminance signals from the television signal output from the video detection circuit and supplies it to a video amplifier circuit 1, the input luminance signal V _in in the video amplifier circuit 1
The pedestal level and contrast are adjusted to drive a cathode ray tube 2 (hereinafter referred to as a CRT (cathode ray tube)) (FIG. 4).

[0004] That video amplifier circuit 1, the input luminance signal V _in through the cutlet pulling capacitor C1 preamplifier (amplifier 3, emitter grounded amplifier stage 4 and the contrast adjustment circuit 5) is input to the input luminance signal V in the pre-amplifier _After the pedestal level of "in" is level-shifted, it is amplified by a power amplifier (differential amplifier 6 and amplifier 7) to drive CRT2.

Here, a reference voltage E1 is applied to the input terminal of the amplifier 3.
And a bias resistor R1 are connected to supply an input bias voltage. Also, the emitter-grounded amplification stage 4 includes transistors Q1 and Q2 forming a differential pair.
The luminance signal V1 amplified by the amplifier 3 is input to the transistor Q1, and the in-phase output of the luminance signal V1 is output from the load resistor _RL to the power amplifier via the contrast adjustment circuit 5. ing.

[0006] Both emitter of factors in transistors Q1 and Q2 are connected through an input resistor R _IN, are adapted by the the input resistor R _IN connexion input dynamic range is set. Also, a contrast adjustment circuit 5
Are transistors Q3, Q4 and Q5, Q5 forming a differential pair.
6, the contrast adjustment voltage ΔE
Each transistor Q3, Q4 and Q based on _CONT
5. The shunt ratio of the collector current flowing through Q6 is controlled to control the gain.

[0007] When the output luminance signal V3 output to the CRT 2 via the attenuator 10 is attenuated, the video amplifier circuit 1 inputs the output luminance signal V3 to the differential amplifier 11, and at the timing of the clamp pulse CLP, the pedestal level of the output luminance signal V3. And the reference voltage V _BRT .

Here, the differential amplifier 11 has a reference voltage V _BRT
By feeding back the comparison output to the differential amplifier 6 so that the pedestal level matches the pedestal level, the pedestal level of the output luminance signal V3 does not have a temperature characteristic.

[0009]

However, in the case of the video amplifier circuit 1, since the input clamp is not performed, the input / output dynamic range of the preamplifier 3 and the input dynamic range of the power amplifier are required, and the output dynamic at the final output stage is required. There was a problem that the microwave range became narrow.

Further, since the input impedance of the video amplifier circuit is several tens of kΩ, an input capacitance of several tens of μF or more is required so that V sag does not occur.

Further, the video amplifying circuit 1 has a problem that an extra clamp current is required to increase the following speed, and the power consumption is increased.

The present invention has been made in view of the above points, and eliminates the temperature characteristics of the pedestal level of the output signal, and does not change the output level even if the pedestal level is changed when a wideband signal is input. A video signal amplifier circuit is proposed.

[0013]

According to a first aspect of the present invention, there is provided a preamplifier for amplifying an input video signal Vin, and an input video signal Vin amplified by the preamplifiers 3, 5 is provided. Main amplifier 7 for power amplification
And an output video signal V3 output from the main amplifier unit 7.
A feedback circuit for comparing the pedestal level of the output video signal with a predetermined variable reference voltage EBRT is fed back to the input video signal Vin, thereby providing a clamp means for controlling the pedestal level of the output video signal V3 to the variable reference voltage EBRT. , A predetermined fixed reference voltage E0 and a variable reference voltage EBR
The input video signal Vin is amplified by using the composite voltage with T as a power supply voltage. In the second invention, the first clamp means 31 for clamping the pedestal level of the input video signal Vin to a predetermined value, and the first clamp means 3
The preamplifiers 3 and 5 amplify the input video signal Vin whose pedestal level is clamped by 1; the main amplifier 7 that power amplifies the input video signal Vin amplified by the preamplifiers 3 and 5; The output video signal V3 is output based on a comparison output between the pedestal level of the output video signal V3 and a predetermined variable reference voltage EBRT.
And a second clamping means 11 for controlling the pedestal level to a variable reference voltage EBRT. In the third invention, the preamplifier 5 is provided with a predetermined fixed reference voltage E0.
The input video signal Vin is amplified using the composite voltage of the variable reference voltage EBRT and the variable reference voltage EBRT as a power supply voltage.

[0014]

According to the first aspect of the present invention, the output of the comparison between the pedestal level of the output video signal V3 output from the main amplifier section 7 and the variable reference voltage EBRT is fed back to the input video signal Vin, and the pedestal level of the output video signal V3 is obtained. To the variable reference voltage EBRT, it is possible to eliminate the temperature characteristic of the pedestal level of the output video signal V3 and to control the output video signal V3 to be constant, and to obtain a predetermined fixed reference voltage EBRT.
0 and the variable reference voltage EBRT are combined into a preamplifier 5
The amplifying operation of the input video signal Vin as the power supply voltage of the power supply voltage allows the preamplifier section 5 to follow the variable reference voltage EBRT even if the variable reference voltage EBRT is varied, thereby maintaining the input clamp.

In the second invention, the input video signal Vin input to the preamplifiers 3 and 5 is clamped to a predetermined value by the first clamping means 31, and the output video signal output from the main amplifier 7 is output. By controlling V3 to the variable reference voltage EBRT by the second clamp means 11, the inputs of the preamplifiers 3 and 5 can be kept constant regardless of the change of the variable reference voltage EBRT.

[0016]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.

(1) First Embodiment In FIG. 1 in which parts corresponding to those in FIG. 4 are assigned the same reference numerals, reference numeral 20 denotes a video amplifier circuit as a whole, and the differential output of the differential amplifier 11 is used as a preamplifier. By feeding back and clamping the input bias voltage of the amplifier 3, temperature characteristics do not occur in the pedestal level in the final output stage.

As a result, the input / output dynamic range of the preamplifier and the output dynamic range of the power amplifier need only be small, and the maximum amplitude can be ensured as the output amplitude of the final output stage.

The input impedance can be increased by input clamping, the input capacitance of the coupling capacitor C1 can be reduced, and the response speed can be improved.

The video amplifier circuit 20 includes a differential amplifier 11
Of the reference voltage V _BRT input to the non-inverting input terminal of the power supply voltage and the load resistance R _L instead of the power supply voltage V _CC and the load resistance R _L
And the other end of the output dynamic range
Even when the luminance is adjusted by fixing the input clamp to 0, the input clamp is hardly detached.

In the above configuration, the video amplifying circuit 20
The amplifier 3 clamps the DC level of the input luminance signal V _{IN to} a predetermined input bias voltage determined by the reference voltage V _BRT.
And the pedestal level of the input luminance signal V _IN is varied to drive the CRT 2 with the drive signal V 3.

Here, when the video amplifier circuit 20 captures the pedestal level of the drive signal V3 supplied to the CRT 2 through the amplifier 7 constituting the final output stage into the differential amplifier 11 at the timing of the clamp pulse, the reference voltage V _BRT
The input bias voltage of the amplifier 3 is increased or decreased based on the differential output.

That is, when the pedestal level is equal to the reference voltage V
_{When the} voltage becomes higher than the _BRT , the differential amplifier 11 raises the input bias voltage of the amplifier 3 so that the transistor Q1
, The collector current flowing through the load resistor _RL is reduced, and the pedestal level of the drive signal V3 is reduced .

The pedestal level is equal to the reference voltage V _BRT
When the voltage becomes lower , the differential amplifier 11 lowers the input bias voltage of the amplifier 3 to increase the base current i supplied from the amplifier 3 to the transistor Q1, thereby increasing the collector current flowing through the load resistor _RL , thereby increasing the drive signal. V
Increase pedestal level of 3.

By this feedback control, the video amplifying circuit 20 can eliminate the temperature characteristic of the pedestal level of the drive signal V3.

The video amplifying circuit 20 can control the reference voltage V when adjusting the brightness of the entire screen displayed on the CRT 2.
By adjusting the voltage of the _BRT , the brightness of the screen can be adjusted.

That is, if the voltage value of the reference voltage V _BRT is increased by ΔE from the current value, the pedestal level of the drive signal V3 is also increased and the entire screen becomes dark . Conversely, if the voltage value is decreased by ΔE, the drive signal V3 is reduced. The smaller the pedestal level is, the brighter the entire screen becomes, and the desired brightness can be adjusted.

In the case of the video amplifying circuit 20, the potential difference between the load resistors _RL for outputting the drive signal V3 is always fixed to a constant voltage E0 even if the voltage value of the reference voltage V _BRT is increased or decreased to adjust the luminance. Therefore, the input clamp does not come off during adjustment.

This is because the power supply potential applied to the load resistor _RL also increases or decreases by ΔE according to the increase or decrease (ΔE) of the reference voltage V _BRT.

That is, if the power supply potential applied to the load resistor R _L is fixed to the reference power supply V _CC and the pedestal level of the drive signal V3 is set to the maximum level V _PDH that can be adjusted by the reference voltage V _BRT , As the bias voltage increases, the output of the amplifier 3 decreases, with the result that the collector current decreases and the pedestal level increases.

If the input bias voltage and the pedestal level at this time are V _INH and V _PDH , respectively, and the input bias voltage of the transistor Q4 of the contrast adjustment circuit 5 is V _INH0 , the input bias voltage V _INH and the pedestal level V _PDH are equal. In the meantime,

(Equation 1) Holds.

If the pedestal level of the drive signal V3 is set to the minimum level _VPDL that can be adjusted by the reference voltage _VBRT , the input bias voltage becomes low and the amplifier 3
Output increases, so that the collector current increases and the pedestal level decreases.

If the input bias voltage and the pedestal level at this time are V _INL and V _PDL , respectively, and the input bias voltage of the transistor Q4 of the contrast adjustment circuit 5 is V _INL0 , the input bias voltage V _INL and the pedestal level V _PDL are equal. In the meantime,

(Equation 2) Holds, and the gain A is used between the two voltages, and the following equation is obtained.

(Equation 3) As shown in FIG. 5, both input bias voltages V
_A voltage difference also occurs between _INH and V _INL .

On the other hand, in the case of the video amplifying circuit 20, the pedestal level has the maximum value V _PDH and the minimum value V _PDH respectively.
_Assuming that the reference voltages for _PDL are V _MAX and V _MIN , both the reference voltages V _MAX and V _MIN and the pedestal level V
It is between _PDH and V _PDL, the following equation

(Equation 4)

(Equation 5) Holds.

In the equations (4) and (5), α
Indicates an amplification degree and an attenuation amount, and can be represented by a change amount between both the amplification degree, the attenuation amount and the reference voltage, and can be set to an arbitrary value.

At this time, the following equation is provided between the voltage difference between the two voltages and the input bias voltage.

(Equation 6) When the constant α is set to 1 and the left side becomes 0, the input bias voltages V _INH and V _INH are set.
_There is no difference between _INLs .

As described above, in the case of the video amplifier circuit 20, even if the reference voltage V _BRT is increased or decreased to adjust the luminance, the input bias voltage does not change, and the input voltage difference of the differential amplifier 6 hardly changes. And the input clamp is hard to come off.

In addition, as a result of the input clamp being less likely to come off, the currents i1 and i2 input / output to / from the amplifier 3 can be reduced, the power consumption is further reduced as compared with the prior art, and the driving capability of the transistors Q1 and Q3 is reduced. Lower ones can be used.

According to the above configuration, the feedback control is performed so that the pedestal level of the drive signal V3 at the input terminal of the CRT 2 matches the reference voltage V _BRT , and the output dynamic range is fixed to the constant voltage E0. The temperature characteristics of the pedestal level can be eliminated, and the possibility that the input clamp will come off even if the luminance is adjusted by increasing or decreasing the reference voltage V _BRT can be effectively eliminated.

(2) Second Embodiment In FIG. 2, in which parts corresponding to those in FIG. 1 are assigned the same reference numerals, reference numeral 30 denotes a video amplifier circuit as a whole, and a luminance signal having a wide frequency band of an input signal is input. In such a case, the output dynamic range is not fluctuated during the brightness adjustment.

In the case of this embodiment, a transistor Q30 cascode-connected to the transistor Q4 is connected between the load resistor _RL and the transistor Q4, and a differential point is provided at a connection point P30 between the transistors Q30 and Q4. The output terminal of the amplifier 11 is connected.

Thus, the video amplifier circuit 30 supplies the collector current I _C flowing to the load resistor _RL by the differential amplifier 11.
The pedestal level is controlled to be constant by controlling the feedback.

Here, the input bias clamp amplifier 31
The input terminal is supplied the output terminal voltage and the reference voltage of the amplifier 3, respectively, as the emitter resistance r _e of the transistor Q1 is fed back controls the input bias voltage of the amplifier 3 to be constant by the amplifier 31 to be constant at all times It has been done.

In this embodiment, the constant voltage E0 controls the hold voltage of the capacitor C30 for supplying the hold voltage to the differential amplifier 6 to be constant regardless of the fluctuation of the reference voltage.

In the above configuration, the video amplifying circuit 30
When the drive signal V3 is taken into the differential amplifier 11 at the timing of the clamp pulse, the drive signal V3 is compared with the reference voltage V _BRT ,
The collector current I _C flowing through the load resistor _RL is controlled so that the pedestal level of the drive signal V3 becomes constant.

At this time, the amplifier 31 compares the output voltage of the amplifier 3 with the reference voltage at the timing of the clamp pulse, and controls the two voltages so as to be equal (that is, by fixing the base potential of the transistor Q1 to the emitter). resistance r by controlling the current constant flowing to _e) controlling the input bias constant gain when the luminance adjustment is made so as not to change.

[0047] For example, for inputting the luminance signal V _IN wide frequency band, the input resistance from the need to widen the frequency band R _IN
And the resistance of the additional resistor R _L must be reduced,
In this case although the emitter resistor r _e of the transistor Q1 can not be ignored with respect to the input resistor R _IN, the gain also varies the luminance for the amplifier 31 is Yotsute emitter resistance r _e is controlled to be constant does not change.

According to the above configuration, the video amplification circuit 20
By clamping the input bias voltage at the input stage of the common base amplifier, the gain can be stabilized regardless of the luminance adjustment, and the temperature characteristics of the pedestal level can be eliminated.

(3) Other Embodiments In the above embodiment, the case where the output dynamic range is fixed to the constant voltage E0 and the input bias voltage of the emitter-grounded amplification stage is clamped has been described. However, the present invention is not limited to this, and can be widely applied to the case where the input bias voltage of the differential amplifier stage is clamped at the timing of the clamp pulse as shown in FIG.

Thus, the video amplifying circuit 40 can secure a wide output dynamic range even when the power supply voltage V _CC is low, and can obtain the same effects as described above.

In the above embodiment, the luminance of the video is adjusted by controlling the pedestal level of the drive signal V3 output from the amplifier 7 to a predetermined potential using the video amplifier circuits 20, 30, and 40. However, the present invention is not limited to this, and may be applied to a case where the grid voltage of the CRT 2 is controlled to a predetermined potential.

Further, in the above-described embodiment, the case where the constant α is set to 1 has been described. However, the present invention is not limited to this. If the constant α is 0.5 or more, the case where the output dynamic range is fixed is not fixed. , The input bias voltage can be reduced.

This is because the difference voltages (V _PDH -V _PDL ) and (V
_MAX− V _MIN ) is approximately equal, so that when the constant α is set to 0.5 or more, the value can be obtained by making the left side of the equation (6) smaller than the left side of the equation (3).

Further, in the above-described embodiment, the case where the present invention is used for pedestal level clamping has been described. However, the present invention is not limited to this, and may be applied to other circuits that shift while keeping the DC level at a constant value. Widely applicable.

[0055]

As described above, according to the present invention, a comparison output between the pedestal level of the output video signal output from the main amplifier and the variable reference voltage is fed back to the input video signal, and the pedestal level of the output video signal is obtained. By controlling the reference voltage to a variable reference voltage, it is possible to eliminate the temperature characteristic of the pedestal level of the output video signal and control the output video signal to be constant, and to combine a predetermined fixed reference voltage and a variable reference voltage with the power supply voltage of the preamplifier section. By performing the amplifying operation on the input video signal, the preamplifier unit can follow the input reference signal even if the variable reference voltage is varied, thereby maintaining the input clamp. Further, the input video signal input to the preamplifier is clamped to a predetermined value by the first clamp means, and the output video signal output from the main amplifier section is controlled to a variable reference voltage. The input of the preamplifier can be kept constant irrespective of the change of.

[Brief description of the drawings]

FIG. 1 is an equivalent circuit diagram showing a first embodiment of a DC level shift circuit according to the present invention.

FIG. 2 is an equivalent circuit diagram showing a second embodiment of the DC level shift circuit according to the present invention.

FIG. 3 is an equivalent circuit diagram showing another embodiment.

FIG. 4 is an equivalent circuit diagram showing a conventional DC level shift circuit.

[Explanation of symbols]

1, 20, 30, 40 ... video amplification circuit, 2 ... CR
T, 3, 7, 11, 31... Amplifier, 5... Contrast adjustment circuit.

Claims (3)

(57) [Claims] (1)A preamplifier section for amplifying the input video signal, The input video signal amplified by the preamplifier section is
A main amplifier section to amplify, The pedestal of the output video signal output from the main amplifier
Increases the comparison output between the star level and the predetermined variable reference voltage.
By feeding back the input video signal,
Set the pedestal level of the output video signal to the variable reference voltage
Clamping means to control and With The preamplifier section includes a predetermined fixed reference voltage and the variable
The input video signal described above, using the composite voltage with the
Amplify A video signal amplifying circuit characterized by the above-mentioned. (2)Predetermined pedestal level of input video signal
First clamping means for clamping to The pedestal level is closed by the first clamping means.
A preamplifier section for amplifying the input video signal that has been ramped
When, The input video signal amplified by the preamplifier section is
A main amplifier section to amplify, The pedestal of the output video signal output from the main amplifier
Based on the comparison output between the starter level and a predetermined variable reference voltage.
The pedestal level of the output video signal
Second clamping means for controlling the variable reference voltage; Equipped with
And a video signal amplifier circuit. 3. The preamplifier according to claim 1, wherein said preamplifier has a predetermined fixed reference voltage.
And the above-mentioned variable reference voltage as a power supply voltage.
3. An amplifying operation for an input video signal.
2. The video signal amplifier circuit according to 1.