JPH0470167A - High frequency corrector - Google Patents

Abstract

PURPOSE:To amplify the amplitude of a high frequency component in an input signal to be larger than a low frequency component without distorting the phase by enlarging a high frequency gain rather than a low frequency gain when amplifying the signal, correcting the phase of the output signal and negatively feeding the corrected signal back to an amplifying means. CONSTITUTION:The output of an amplifier 1 in the first step is inputted, and an amplifier 2 as the first amplifying means to enlarge the high frequency gain rather than the low frequency gain enlarges the high frequency gain when amplifying the signal rather than the low frequency gain. Then, a delay phase shifting means 4 corrects the phase of the output signal. The phase-corrected signal is negatively fed back to the amplifying means 2. Thus, without distorting the phase of the input signal, the amplitude of the high frequency component can be amplified larger than that of the low frequency component.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a high frequency correction device that performs high frequency correction in video cameras, video display devices, and the like.

BACKGROUND ART For example, in an image pickup tube, the scanning beam diameter is large, so the high frequency components of the video output signal are lower than the low frequency components.

Therefore, it is necessary to increase the amplitude of only the high frequency component of the video output signal.

FIG. 2 is a block diagram of a conventional aperture correction device for performing this correction. The conventional technology will be explained below based on FIG.

In the figure, l is the signal source of the video signal, 2 is the signal divider connected to the signal R1, 3 is the first amplifier circuit connected to the signal divider 2, and 4 is the differential circuit connected to the signal divider 2. 5 is a delay circuit connected to the differentiating circuit 4; 6 is a second amplifier circuit connected to the delay circuit 5; 7 is a second amplifier circuit 6;
and an adder circuit connected to the first amplifier circuit 3.

Next, the operation of this high frequency correction device will be explained.

The human signal is distributed by a signal distributor 2 to a first amplifier circuit 3 and a differentiation circuit 4. Since the differentiating circuit 4 consists of a series circuit of a capacitor and a resistor, the output signal is a differentiated version of the input signal.

Therefore, the signal has fewer low-frequency components and enhanced high-frequency components. Due to differentiation, this signal has a phase of π/
Since it advances by 2, the delay circuit 5 returns it to its original phase. Thereafter, it is amplified by the second amplifier circuit 6. Further, the output signals of the first amplifier circuit 3 and the second amplifier circuit 6, which input and amplify the signal from the signal divider 2, are added together in the adder circuit 7. As a result, the output signal becomes one in which the high frequency components of the original input signal are emphasized.

Problems to be Solved by the Invention However, the phase lead of the differentiating circuit 4 is π/2 regardless of the frequency.

On the other hand, there is no known delay circuit 5 in which the phase delay is π/2 regardless of the frequency. That is, in the conventional technology, a distributed constant delay line is often used as an example of the delay circuit 5. The delay line remains closed during the delay,
For example, if it is 20 nS, the frequency corresponding to π/2 is 12.5 MH2, so if it is other than 12.5 MH2, there is a problem that the aperture correction output has a phase lag other than π/2 and phase distortion occurs.

An object of the present invention is to provide a high frequency correction device that solves the problems of the conventional high frequency correction device.

Means for Solving the Problems The high frequency correction device of the present invention includes a first amplification means that makes a high frequency gain larger than a low frequency gain when amplifying a signal, and a delay phase shift means that corrects the phase of the output signal. and negative feedback means for negatively feeding back the phase-corrected signal to the amplification means.

Effect of the present invention The first amplification means makes the high frequency gain larger than the low frequency gain when amplifying the signal, the delay phase shift means corrects the phase of the output signal, and the negative feedback means corrects the phase. The obtained signal is negatively fed back to the amplification means.

Thereby, the amplitude of the high frequency component can be amplified to be larger than the amplitude of the low frequency component without causing phase distortion in the input signal.

Example Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a circuit diagram of an embodiment of the high frequency correction device of the present invention.

In Figure 1, 1 is the first stage amplifier, and 2 is the first stage amplifier l.
An amplifier as a first amplification means which inputs the output of the amplifier 2 and makes the high frequency gain larger than the low frequency gain; 3 is a buffer for receiving and receiving the signal from the amplifier 2; 4 is a buffer for delaying the phase of the input signal from the buffer; Delay phase shifter 5 is a second amplification means for amplifying the output signal of the delay phase shifter 4; Reference numeral 6 filters the output signal of the second amplifier 5. A filter is a filtering means that passes high-frequency components. The output of the filter 6 is negatively fed back to the amplifier 1.

Amplifier] consists of a differential amplifier circuit. 1] is a first transistor that amplifies the input signal, 12 is a second transistor that amplifies the negative feedback signal, and 13 is a third transistor that serves as a constant current source.
, and 14 is a load resistor. Since the differential amplifier circuit has a high input impedance, it is possible to create a high-bandwidth, high-gain amplifier. The load resistance 14 is adjusted according to the difference in input between the first transistor 11 and the second transistor 12.
Since current flows through the circuit, if the two inputs are in phase, it becomes a negative feedback circuit. Note that as a negative feedback circuit, there is a method in which two inputs are set in opposite phases to each other and applied to one input terminal, but the output characteristics are better when a differential amplifier circuit is used.

The amplifier 2 is composed of an emitter peaking circuit and a collector peaking circuit. 21 is the first stage transistor, 22
is a transistor in the latter stage, 23 is a load resistance in the first stage, 24 is an emitter resistor for negative feedback, 25 is a bypass capacitor,
26 is a load resistance at the subsequent stage, 27 is a load coil, and 28 is an emitter resistance. The first-stage transistor 21 has a base current proportional to the emitter admittance, and the load 23 obtains an output voltage proportional to the base current.

Therefore, the voltage gain G1 increases the emitter admittance by JωC
+ + 1/R+, if the load is R2, G
Yi=(1+j ωC+R+) R2/ R+
(1).

Since the base current of the transistor 22 in the latter stage is proportional to the input voltage, the output voltage is proportional to the load impedance. If the load impedance is Rv + jωL and the emitter resistance is R4, then the voltage gain G2 at the subsequent stage is G2=(1+j(,)L/R3)R3/R4(2).

Therefore, the overall gain G of amplifier 2 is G 1X G 2 and G=C1! (1+jua) (1+j ωb)
(3) Kushi C; ! I= (R2・R3) /
(R1-Ra>a”C+R+ b=L/Rt
becomes.

If we choose a constant so that a=b, then from equation (3) we get =Ge
(1++a 2 a 2) ・E”
(4) φ=t,,l
(ωa) and -), it can be seen that the phase advances as the output amplitude increases with the frequency.

The delay phase shifter 4 divides the human input signal using two voltage dividing circuits and amplifies it using a differential amplifier circuit. Reference numeral 41 denotes a differential amplifier circuit, which has the same configuration as the amplifier l.

42.43 are the first and second resistors that divide the human power signal, 4
4 is a resistor, and 45 is a capacitor.

Since the input impedance of the differential amplifier circuit 41 is sufficiently large, if the values of the first and second resistors 42 and 43 are made equal,
Half of the original human input signal is applied to one input end. A voltage divided by a capacitor 45 of a resistor 44 is applied to the other input terminal. If the input signal is 5, the resistor is R, and the capacitor is C, the differential power V at the two input terminals of the differential amplifier circuit 41 is as follows.

Since the output of the differential amplifier circuit vi44m is proportional to the differential input, the output V@ is, and the gain A of the N phase shifter 4 is expressed by equation (5), where (1+jωCR) and (1-jbicR) are 1.
Since it is a yoke, the absolute values are equal and the phases are opposite. Therefore, equation (5) can be expressed as the following equation, and it can be seen that this circuit becomes a delay phase shifter.

A = A o42# (e) However, θ = tan ωCR If a in equation (4) and CR in equation (6) are made equal, the overall characteristics of amplifier 2 and delay phase shifter 4 are (4) It is expressed as the product of formula and (5), AC=AoGo(1+ca"a2) (7) where a = CR= C+ R+ :' L / R
z, which means that the characteristics of high frequency correction are not satisfied.

Note that the high-frequency gain of the circuit is reduced by the stray capacitance of each circuit, the collector capacitance of the transistor, and the cut-off frequency of the transistor, so it is unclear at which frequency the gain given by equation (7) is maximum. It is.

The amplifier 5 is an amplifier whose voltage gain is less than 1 and applies the output of the delay phase shifter 4 to the second transistor 12 of the amplifier 1. This negative feedback compensates for the reduction in high frequency gain due to the above-mentioned stray capacitance, etc., and has the effect of lowering the overall gain expressed by equation (7). That is, for example, if the low frequency gain of this amplifier 5 is lowered, only the high frequency component will be negatively fed back, and as a result, the high frequency gain will be relatively lowered in the overall gain, and the effect of aperture correction will be lowered. Therefore, by providing means for controlling the gain of the amplifier 5, the aperture correction effect can be freely controlled.

The high-pass filter 6 is provided to completely eliminate the amount of negative feedback of low frequency components to the amplifier 1. If the low frequency gain is lowered by the amplifier 5, the phase of the low frequency output will advance significantly, so it is desirable to eliminate the feedback energy by using the high pass filter 6. Note that high frequency components can also be processed in the same way.

Effects of the Invention According to the present invention, the amplitude of the high frequency component of a human input signal can be amplified to a greater extent than the low frequency component without phase distortion.

Furthermore, the total gain can be maximized at any frequency, and the high frequency correction effect can be changed arbitrarily.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the high frequency correction device of the present invention, and FIG. 2 is a block diagram of a conventional aperture correction device. 1.2.5...Amplifier, 3...Buffer, 4...
Delay phase shifter, 6... High pass filter, 11.12.1
3.21,22...transistor, 14.24.26
．． 28.42.43.44...Resistance, 25.45.
...Capacitor, 27...Coil.

Claims (3)

[Claims] (1) A first amplification means that makes a high frequency gain larger than a low frequency gain when amplifying a signal, a delay phase shift means that corrects the phase of the output signal, and a phase-corrected signal that is transmitted to the amplification means. A high frequency correction device characterized by comprising negative feedback means for providing negative feedback. (2) The high frequency correction according to claim 1, wherein the signal to be negatively fed back to the first amplification means is amplified by the second amplification means, and the amount of negative feedback is adjusted by making the amplification gain variable. Device. (3) The high frequency correction device according to claim 1, wherein the output signal of the second amplifying means is input to a filtering means and the selected frequency component is negatively fed back to the first amplifying means.