JPS63274208A - Expander circuit - Google Patents

Abstract

PURPOSE:To obtain an expanded output with a desired nonlinear characteristic even with an input signal with a low level by constituting the titled circuit of a differential amplifier receiving an input signal, a lead/lag filter, an inverse amplifier and a couple of diodes of anti-parallel connection. CONSTITUTION:An input signal is given to a differential amplifier section 22 and an inverse amplifier section 27 and a prescribed level/frequency characteristic is given to an output signal of the amplifier section 27 by lead/lag filters 30, 33 and the result is fed to the input of the amplifier section 22 through a diode circuit 40. Thus, a level over a prescribed level at a prescribed frequency component selected by a filter section among an amplifier output signal of the amplification section 27 is fed in opposite phase with respect to the input signal to an input terminal of he amplifier section 22. Thus, the level of a portion of an output signal of the amplifier section 22 having a prescribed level or over in a predetermined frequency component in the input signal is expanded. Since the input signal is applied to the circuit 40 while being amplified, even if the input signal level is small, the circuit is operated normally.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an expander circuit having frequency selection characteristics, which is used in a luminance signal reproduction system in a video tape recorder.

(Summary of the Invention) The present invention provides an expander circuit having frequency selection characteristics used, for example, in a reproduction luminance signal path in a recording system of a video tape recorder, in which a human input signal is input to one of a pair of input terminals in a differential amplifier section. A predetermined frequency component in the amplified output signal obtained at the output end of the anti-phase amplification section is supplied to the input end of the anti-phase amplification section, and is obtained at the output end of the anti-phase amplification section. The signal supplied to the common connection terminal and obtained at the other common connection terminal of the pair of diodes is supplied to the other of the pair of input terminals in the differential amplification section, and the signal obtained from the output terminal of the differential amplification section selects a frequency. By extracting the output signal whose components have been expanded,
Even when the level of the input signal is relatively low, an expanded output with desired nonlinear characteristics can be obtained, and the frequency characteristics and expansion characteristics of the output signal can be easily adjusted. It is something.

(Prior Art) When a video tape recorder records a composite video signal containing a luminance signal and a carrier color signal, an FM luminance signal is obtained by frequency modulating a predetermined carrier signal with a luminance signal. As the signal is formed, the carrier chrominance signal is frequency converted to have a frequency band below the frequency band of the FM luminance signal to form a low-pass converted chrominance signal, which is combined with the FM luminance signal. A system in which low-frequency conversion color signals are recorded on a magnetic tape with a large number of inclined tracks is widely used.

In such a case, F in the recording system of the video tape recorder.
When the M luminance signal is formed, -S is used to improve the signal-to-noise ratio (S/N ratio) of high-frequency components in the luminance signal reproduced by the reproduction system of the video tape recorder from the recorded magnetic tape. In order to achieve this, pre-emphasis processing is applied to the luminance signal to be subjected to frequency modulation.
The level of the high frequency component of the luminance signal is emphasized.

However, the luminance signal that has been subjected to pre-emphasis processing has a sharp overshoot in the rising part to the white level and the falling part to the black level, and if it is directly subjected to frequency modulation, the FM luminance signal will have an overshoot. There is a risk that a modulated portion will occur, resulting in an undesirable inversion phenomenon during reproduction. Therefore, the luminance signal that has been subjected to pre-emphasis processing is usually supplied to a clipping circuit so that the overshoot portion above a certain level is clipped, and then the luminance signal is subjected to frequency modulation.

Based on the luminance signal that has been subjected to such pre-emphasis processing and clipping processing, <FM! In a video tape recorder playback system that reproduces a luminance signal and a carrier color signal from a magnetic tape on which an i-degree signal is recorded together with a low frequency conversion color signal, the FMi 1-degree signal read from the magnetic tape is demodulated by the number of returned signals. De-emphasis processing is performed on the demodulated luminance signal in order to restore the parts emphasized by pre-emphasis processing in the recording system. At that time, if the demodulated luminance signal is directly subjected to de-emphasis processing, the effect of the portion lost due to the clip processing performed after the pre-emphasis processing in the recording system will be reflected as a lack of high-frequency components in the reproduced luminance signal. As a result, the waveform of the reproduced luminance signal deteriorates. Therefore, in order to avoid such waveform deterioration of the reproduced luminance signal, in the reproduction system, the demodulated luminance signal is supplied to the expander circuit before de-emphasis processing, and the level of the high frequency component is adjusted with non-linear characteristics. Expansion processing is performed, and the demodulated luminance signal is corrected by an expander circuit for the portion lost due to clip processing in the recording system.
The image is subjected to de-emphasis processing.

In this way, the expander circuit used in the playback system of a video tape recorder has conventionally
It is as shown in the figure.

The expander circuit shown in FIG.
1 is provided with its collector connected to the power supply 1B via a load resistor 12, and whose emitter is grounded via an emitter resistor 13, and a resistor is connected to the emitter of this transistor 11 via a capacitor 14. Series connection between 15 and diode 16, and resistor 17 and diode 18
are connected in series and in parallel. Resistance.

Series connection of resistor 15 and diode 16, and resistor 17
One end of each of the series connections between the diode 16 and the diode 18 is grounded, and the diode 16 and the diode 18 have opposite polarities. The demodulated luminance (No. 3) is supplied from the input terminal 9 provided at the base of the transistor 11, is amplified by an amplifier including the transistor 11, and is output to the output terminal 20. For components of the demodulated luminance signal to be amplified that are higher than a predetermined frequency set according to the capacitor 14, the portion having a level at which the diode 16 or the diode 18 is turned on is connected to the diode 16 or the diode 1. 8 is turned on, the gain of the amplifier including the transistor 11 is increased, and its level is expanded. As the level of high-frequency components higher than the frequency increases, the signal is expanded with non-linear characteristics.

(Problems to be Solved by the Invention) However, in the conventionally proposed expander circuits as described above, in order for the diodes 16 and 18 to be turned on, a predetermined amount of water is added to the diodes 16 and 18. It is necessary that the high-frequency components above the frequency have a peak-to-peak level of 2 Vd or more (Vd is the forward conduction voltage of diodes 16 and 18, respectively), and therefore, it is desirable to have a comparative This method is disadvantageous in that it is difficult to apply it to a circuit configuration that operates under a relatively low power supply voltage and transmits low-level signals with a small dynamic range.

In view of this, the present invention utilizes the on/off operation of a pair of diodes arranged in parallel with opposite polarities to expand the level of a predetermined frequency component in an input signal with nonlinear characteristics. Moreover, it is an object of the present invention to provide an expander circuit that operates under a relatively low power supply voltage and can be easily applied to a circuit configuration that transmits low-level signals with a small dynamic range. .

(Means for Solving the Problems) In order to achieve the above-mentioned object, an expander circuit according to the present invention includes a differential amplifier section in which a human input signal is supplied to one of a pair of input terminals, and a differential amplifier section in which a human input signal is supplied to one of a pair of input ends. An anti-phase amplification section that generates an amplified output signal of an anti-phase with respect to the amplified output signal of the anti-phase amplification section, and a filter section that gives a predetermined level-frequency characteristic to the amplified output signal of the anti-phase amplification section are connected in parallel with each other with opposite polarities. First
and a second common connection end, a pair of diodes arranged between the differential amplification section and the anti-phase amplification section, and an output section provided at the output end of the differential amplification section. a pair of diodes, the amplified output signal of the anti-phase amplification section is supplied to the first common connection end with a predetermined level-frequency characteristic, and the obtained signal is supplied to the second common connection end of the pair of diodes to the differential amplification section. The output signal is supplied to the other of the pair of input terminals in the filter section, and an output signal that has been subjected to expansion processing on a frequency component determined by the filter section is taken out from the output section.

(Function) In the expander circuit according to the present invention configured as described above, an input signal is supplied to one input terminal of the differential amplifier section, and the same input signal is supplied to the other input terminal in reverse. The amplified output signal of the anti-phase amplification section obtained by being supplied to the phase amplification section is supplied through a pair of parallel-connected diodes while being given a predetermined level-frequency characteristic by the filter section. As a result, the level part of the predetermined frequency component selected by the filter section of the amplified output signal of the anti-phase amplification section is transmitted to the other input terminal of the differential amplification section. The input signal supplied to the input terminal is supplied with a negative phase relationship, so that the output signal obtained at the output terminal of the differential amplifier section is It is obtained by amplifying a portion of a predetermined frequency component having a level equal to or higher than a predetermined value while being level-expanded. Therefore, from the output section, a signal is obtained which has been subjected to level expansion with nonlinear characteristics for a predetermined frequency component in the input signal.

Under such circumstances, the input signal is amplified by the anti-phase amplifier and supplied to the pair of diodes, so the entire circuit is
It operates normally even when the input signal level is relatively low, so it is suitable for circuit configurations that operate with a relatively low power supply voltage and transmit low-level signals with a small dynamic range. It is assumed that it can be easily applied.

Furthermore, by setting the frequency characteristics of the filter section and setting the gain of the negative phase amplification section, the frequency characteristics and expansion characteristics of the output signal can be easily adjusted.

(Embodiment) FIG. 1 shows the basic configuration of an example of an expander circuit according to the present invention. In this example, from the input terminal 21,
For example, an input signal Si, which is a demodulated luminance signal in a reproduction system of a video tape recorder, is introduced, and the human input signal Si is supplied to one input terminal of the operational amplifier section 22, and the output terminal of the operational amplifier section 22 is inputted. An output signal SO, which is an amplified luminance signal, is obtained from the output terminal 22, and is delivered to an output terminal 23 connected to the output terminal of the operational amplification section 22.

The differential amplifier section 22 is provided with a negative feedback path from its output end to the other input end via the resistor 24, and
The other input end is grounded via a resistor 25.

The input signal Si introduced from the input terminal 21 is also supplied to one input terminal of the differential amplifier section 27 via the resistor 26. A predetermined bias voltage is applied to the other input end of the differential amplifying section 27 by a bias power supply 28, and the differential amplifying section 27 forms an anti-phase amplifying section. The differential amplifier 27 is provided with a negative feedback path from its output end to one input end to which the input signal Si is supplied via a parallel connection of a resistor 29 and a lead-lag filter 30. ing. The lead-lag filter 30 has, for example, a level L-frequency f characteristic shown in FIG. Therefore, the differential amplifier section 27 takes a high gain for frequency components below the frequency fa, and takes a low gain for frequency components above the frequency rb. , and has lag lead amplification characteristics.

The output terminal of the differential amplifier section 27 includes a pair of diodes 31 and 32 connected in parallel with mutually opposite polarities, and
It is connected to the other input terminal of the differential amplifier section 22 through the lead-lag filter 33 . For example, the lead-lag filter 33 has a level-to-frequency characteristic shown in FIG. It is said to have a lead-lag characteristic that takes a high level in a frequency range equal to or higher than the lower frequency fd.By connecting the diodes 31 and 32 in parallel and disposing the lead-lag filter 33, the differential amplifier 27 Frequency component 1 of the output signal determined according to the lead-lag filters 30 and 33, for example, a frequency component in a frequency range of about 200kHz-IMHz, is the common connection on the differential amplifier section 27 side in the parallel connection of the diodes 31 and 32. The diodes 31 and 32 are turned on when the frequency component has a peak-to-peak level of 2Vd'(Vd' is the forward conduction voltage of each of the diodes 31 and 32) or more. , the level portion of the frequency component supplied to the diodes 31 and 32 of 2Vd' or higher is supplied to the diode 3
Lead-lag filter 3 in parallel connection of 1 and 32
The signals are supplied from the common connection terminals of the three examples to the other input terminal of the differential amplification section 22 in a reverse phase relationship with respect to the input signal Si supplied to the one input terminal.

In this way, the differential amplifying section 27 is connected to the other input terminal of the differential amplifying section 22 to which the input signal St is supplied to one input terminal.
Of the output signals of -drag filters 30 and 33
The output signal So obtained at the output terminal of the differential amplification section 22 by supplying a level portion of a predetermined frequency component determined according to the predetermined frequency component according to It is obtained by amplifying a portion of a predetermined frequency component determined according to 30 and 33 having a level equal to or higher than a predetermined value while being level-expanded.

That is, at the output end of the differential amplification section 22, the human input signal Si is
A predetermined frequency component therein is level-expanded with non-linear characteristics, and an amplified output signal SO is obtained, which is sent to the output terminal 2.
It is taken out on 3rd.

During such operation, the input signal Si is supplied to the parallel connection of the diodes 31 and 32.
7, the human signal Si
Even when the level of the input signal Si is relatively low, the level is sufficient to turn on the diodes 3I and 32. Therefore, even when the level of the input signal Si is relatively low, the circuit The whole thing will work normally. Further, from the output end of the differential amplifier section 27 to the differential amplifier section 2
The frequency band and level of the signal supplied to the other input terminal of 2 can be adjusted by setting the frequency characteristics of the lead-lag filters 30 and 33 and setting the gain of the differential amplification section 27. This means that the frequency characteristics and expansion characteristics of the output signal SO obtained at the output end of the differential amplifier section 22 can be easily adjusted.

FIG. 3 shows a specific configuration example of an expander circuit according to the present invention. Comparing the basic configuration shown in FIG. 1 with this specific configuration example, the differential amplifier section 22 in FIG. 1 has transistors 41 and 42 . It is formed by a current source 43 commonly connected to the emitters of each of the transistors 41 and 42, and transistors 44 and 45 forming a current mirror connected to the collectors of each of the transistors 41 and 42, and an input terminal. Transistor 41 connected to 2I
The base of the transistor 4 is used as one input terminal, and the transistor 4
20 base is the other input end. The negative feedback path from the output end of the differential amplifier section 22 to the other input end is
The transistor 46 is formed by a resistor 47 and a current source 48.

In addition, the differential amplifying section 27 in FIG. 1 includes transistors 51 and 52 whose emitters are commonly connected; The base of the transistor 51 is connected to the input terminal 21 via the resistor 26, and one input terminal is the base of the transistor 51, which is connected to the input terminal 21 via the resistor 26. The base of the transistor 52 to which the transistor 28 is connected is the other input terminal. A negative feedback path including the lead-lag filter 30 from the output end of the differential amplifier section 27 to the other input end is connected to the transistor 56. Resistance 57. It is formed by a capacitor 58 and a current source 59.

Furthermore, the lead-lag filter 33 in FIG.
The emitter of a transistor 56, which is formed by a portion including a resistor 49 and a capacitor 50 and serves as an output end of the differential amplification section 27, is connected in parallel with diodes 31 and 32 and a resistor forming a lead-lag filter 33. 49
It is connected to the base of the transistor 42, which is the other input terminal of the differential amplification section 22, via the capacitor 50 and the capacitor 50. The output terminal 23 is connected to the emitter of the transistor 46, which is the output terminal of the differential amplification section 22.

(Effects of the Invention) As is clear from the above description, the expander circuit according to the present invention utilizes the on/off operation of a pair of diodes connected in parallel with opposite polarities to When performing level expansion with non-linear characteristics for a predetermined frequency component, even when the input signal is at a relatively low level, the on/off operation of a pair of diodes is performed appropriately and the entire circuit operates normally. can be done. Therefore, the expander circuit according to the present invention can be easily applied to a circuit configuration that operates under a relatively low power supply voltage and transmits low-level signals with a small dynamic range, and It is ideal for use in level expansion prior to de-emphasis processing of demodulated luminance signals in the re-sweetening system of recorders.

Further, according to the expander circuit according to the present invention, the frequency characteristics and expansion characteristics of the output signal can be easily adjusted by setting the frequency characteristics and gain of the filter section and the anti-phase amplifier section included in the expander circuit. There are also benefits that can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block configuration diagram showing the basic configuration of an example of an expander circuit according to the present invention, FIG. 2 is a characteristic diagram for explaining the filter used in the example shown in FIG. 1, and FIG.
This figure is a circuit connection diagram showing a specific configuration example of the example shown in FIG. 1, and FIG. 4 is a circuit connection diagram showing a conventionally proposed expander circuit. In the figure, 21 is an input terminal, 22 and 27 are differential amplifier sections, 2
3 is an output terminal, 24, 25, 26 and 29 are resistors, 30
and 33 are lead-lag filters, and 31 and 32 are diodes.

Claims (1)

[Claims] A differential amplification section to which an input signal is supplied to one of a pair of input terminals; and a negative phase amplifier to which the input signal is supplied and an amplified output signal having a phase opposite to the input signal is obtained. a filter section that gives a predetermined level-frequency characteristic to the amplified output signal of the anti-phase amplification section; A pair of common connection terminals to which the amplified output signal of the anti-phase amplification section is supplied, and a signal obtained at the second common connection terminal to the other of the pair of input terminals in the differential amplification section. An expander circuit comprising: a diode; and an output section for extracting an output signal subjected to expansion processing on a frequency component selected by the filter section from an output end of the differential amplification section.