JP2944063B2 - Filter device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides an input signal to a plurality of band-pass filters each having a different pass band and having a desired pass band, and extracts a desired pass band component from the input signal. To a filter device.

[0002]

2. Description of the Related Art A filter device as described above is, for example,
It may be provided at the last stage of the variable frequency television modulator used in the joint hearing facility. In such a variable frequency television modulator, as shown in FIG. 3, the video signal supplied to the video input terminal 2 and the audio signal supplied to the audio input terminal 4 are supplied to the modulation unit 6, These modulate the video carrier and the audio carrier to generate a video modulation signal and an audio modulation signal.

[0003] The video modulation signal and the audio modulation signal output from the modulation section 6 are supplied to a frequency conversion section 8. The frequency conversion unit 8 is supplied with a first local oscillation signal having a fixed frequency from the first local oscillation unit 10. Frequency converter 8
Converts the video and audio modulation signals into video and audio intermediate frequency signals using the first local oscillation signal.

The video and audio intermediate frequency signals are supplied to a frequency converter 14 via a band pass filter 12. The frequency conversion unit 14 is supplied with a second local oscillation signal whose frequency is variable from a second local oscillation unit 16. The frequency converter 14 frequency-converts the video and audio intermediate frequency signals into video and audio high-frequency signals according to the second local oscillation signal.

The second local oscillation section 16 generates a second local oscillation signal of any one of n different frequencies in accordance with the channel selection signal from the channel selection section 18. The n frequencies are selected such that the video and audio intermediate frequency signals can be respectively frequency-converted into video and audio high frequency signals of any one of the predetermined n channels.

The video and audio high-frequency signals from the frequency conversion unit 14 are supplied to an amplification unit 22 of a filter device 21 via a low-pass filter 20, and after being amplified there, the signal level is changed by a variable attenuation unit 24. After the adjustment, the signal is further amplified by the amplifier 26. Reference numeral 28 denotes a variable resistor for adjusting the amount of attenuation of the variable attenuation unit 24.

The output signal of the amplifying section 26 is supplied to bandpass filters 32, 34, 36,
38. For example, if the lowest frequency to the highest frequency of n channels is 50 to 450 MHz, the pass band of the band-pass filter 32 is 50 to 90 M
Hz, the pass band of the band-pass filter 34 is 90 to 15
0 MHz, the pass band of the band pass filter 36 is 150 to 250 MHz, and the pass band of the band pass filter 38 is 2
The frequency is set to 50 to 450 MHz.

Each band-pass filter 32, 34, 36, 3
Numeral 8 denotes a current-carrying type. The channel selection signal is transmitted from the channel selection unit 18 to the second local oscillation unit 16 so that the video and audio intermediate frequency signals are converted into one channel a within 50 to 90 MHz, for example. Is supplied to the band-pass filter 32 from the channel selection unit 18.
Is supplied with a DC voltage.

The DC voltage is supplied to a PIN diode 40 provided on the input side and the output side of the band-pass filter 32.
From 42 flows to resistors 44 and 46. As a result, PIN
The diodes 40 and 42 become conductive, and the output signal of the amplifier 26 is supplied to the band-pass filter 32, and the output signal of the
The video and audio high frequency signals of one channel a in z are extracted from the band pass filter 32 and supplied to the output terminal 48.

Therefore, for example, it is possible to prevent the spurious components of the video and audio high-frequency signals of the channel a from being output from the output terminal 48. Even when the frequency is converted to another channel in the range of 50 to 90 MHz, the PIN diodes 40 and 42 are turned on in the same manner as described above, and the output of the spurious component by the band-pass filter 32 can be suppressed.

To convert the video and audio intermediate frequency signals to one channel b within 90 to 150 MHz, a DC voltage is similarly supplied from the channel selector 18 to the band-pass filter 34, and the PIN diode 5
0 and 52 conduct. When converting the video and audio intermediate frequency signal to one channel c within 150 to 250 MHz, a DC voltage is supplied from the channel selection unit 18 to the band-pass filter 36, and the PIN diodes 54, 5
6 conducts. When converting the video and audio intermediate frequency signals to the channel d in the range of 250 to 450 MHz, the DC voltage is supplied from the channel selection unit 18 to the band-pass filter 3.
8 and the PIN diodes 58 and 60 conduct.

Therefore, the band-pass filters 34, 36, 3
8, a channel b from which spurious components have been removed,
The video and audio high frequency signals of c and d are supplied to the output terminal 48.

[0013]

However, in such a variable frequency television modulator, the output levels of the respective channels a to d generated at the output terminal 48 vary as shown in FIG. 4, for example. This is because the conversion loss in the frequency converter 14 and the gain of the amplifiers 22 and 26 are slightly different depending on the frequency, and the filters 32, 34, 36 and 38
Is different for each filter. Since the variable attenuator 24 is provided, it is possible to adjust the output level by adjusting the amount of attenuation. However, the variable attenuator 24 adjusts the levels of all video and audio high-frequency signals of each of the channels a to d. Therefore, for example, since the video and audio high-frequency signals of channel a are converted, the video and audio high-frequency signals of channel a are converted to, for example, channel b while the variable attenuator 24 is adjusted so that the video and audio high-frequency signals have a desired level. If it becomes necessary, the attenuation of the variable attenuator 24 must be adjusted again, and it is necessary to readjust the level every time the channel is changed, which is troublesome. Was.

[0014]

According to the present invention, there is provided an input terminal to which an input signal having a signal level different according to a frequency is supplied, an output terminal, and filter parallel means. Have been. This filter parallel means connects a plurality of band-pass filter means in parallel, and each band-pass filter means has a different pass band, and when a filter energizing signal is supplied, the band-pass filter means falls within its own pass band. The above-mentioned input signal of the frequency of each is extracted. A gain adjusting means is provided between the input terminal and the output terminal in series with the filter parallel means. The gain adjusting means adjusts the gain to a value according to the gain adjustment signal. The gain adjusting means is provided with a gain adjusting signal generating means corresponding to each band pass filter means. The gain adjustment signal generating means generates the gain adjustment signal when the gain adjustment energizing signal is supplied. Control means for simultaneously supplying the filter energizing signal and the gain adjusting energizing signal to the corresponding band-pass filter means and the gain adjusting signal generating means are provided. The gain adjustment signal generated by each gain adjustment signal generation means has a signal level at the output terminal even when any of the bandpass filter means is energized.
Each is selected so as to be substantially at a predetermined level.

[0015]

According to the present invention, the gain adjustment signal generated by each gain adjustment signal generation means has a signal level at the output terminal whichever band-pass filter means is activated.
Each is selected so as to be substantially at a predetermined level. Therefore, the band-pass filter means for passing the frequency of the signal supplied to the input terminal is energized by the filter energizing signal from the control means, and at the same time, the gain adjustment is energized by the gain adjustment energizing signal from the control means. The signal level at the output terminal becomes substantially a predetermined level due to the gain adjustment signal generated by the signal generating means.

[0016]

This embodiment relates to a frequency variable television modulator as shown in FIG.
The same reference numerals are given to the same parts as those in the configuration shown in FIG. 3, and the description thereof will be omitted. In FIG. 1, reference numeral 59 denotes an input terminal through which an output signal of the low-pass filter 20 is supplied to the amplifier 22.

The variable attenuator 24a provided between the amplifiers 22 and 26 functions as a gain adjuster, and
It is a π type using diodes 62, 64 and 66. The cathode of the PIN diode 62 is connected to the output side of the amplifier 22 via a DC blocking capacitor 68, and the anode is connected to the amplifier 2 via DC blocking capacitors 70 and 72.
6 is connected to the input side.

The anode of the PIN diode 64 is connected to the connection point between the DC blocking capacitors 70 and 72, and the cathode is grounded via the high-frequency grounding capacitor 74. Also, a PIN is connected to the cathode side of the PIN diode 62.
The cathode of the diode 66 is connected, and the anode is grounded via a high-frequency grounding capacitor 76.

Further, a high frequency blocking coil 78 is connected between the cathode of the PIN diode 64 and the anode of the PIN diode 66, and the PIN diodes 62, 6
The interconnection point of the six cathodes is grounded through a resistor 80. A voltage obtained by dividing the DC voltage + Vc by resistors 82, 84 and 86 is applied to an interconnection point between the anode of the PIN diode 64 and the DC blocking capacitors 70 and 72.

Therefore, a DC current flows through the PIN diode 64, the high-frequency blocking coil 78, the PIN diode 66, and the resistor 80, and the PIN diodes 64 and 66 generate a high-frequency resistance value determined by the current value flowing through them. I have.

On the anode side of the PIN diode 62,
A variable resistor 28 for adjusting the amount of attenuation is connected, and a DC current having a value determined by adjusting the value of the variable resistor 28 flows through the PIN diode 62 and the resistor 80. Generate a high-frequency resistance value according to the value. Since this high-frequency resistance value can be varied by adjusting the variable resistor 28, the variable attenuator 24
The amount of attenuation at a can be varied.

The variable resistor 28 includes another variable resistor 8
8, 90, 92, 94 are connected to one end of each of the variable resistors 88, 90, 92, 94 via the collector-emitter conductive paths of the switching transistors 96, 98, 100, 102. DC voltage + Vc is applied. These variable resistors 88, 90, 92, 94 and switching transistors 96, 98, 100, 102
Function as gain adjustment signal generating means.

A switch circuit 112 is provided in the channel selection section 18. This switch circuit 112
Generates a DC voltage + Vc at an output terminal 104 when generating a second local oscillation signal for generating a video and audio high frequency output signal within 50 MHz to 90 MHz,
When a second local oscillation signal for generating a video and audio high-frequency output signal in a frequency range of 150 to 250 MHz is generated, a DC voltage + Vc is generated at an output terminal 106, and a video and audio high-frequency output signal in a frequency range of 150 to 250 MHz is generated. When the second local oscillation signal is generated, the DC voltage +
Vc is generated at the output terminal 108,
When a second local oscillation signal for generating a video and audio high frequency output signal within 0 MHz is generated, a DC voltage + Vc is generated at the output terminal 110.

The output terminal 104 is connected to the conduction type bandpass filter 32 and to the base of the switching transistor 96 via the resistor 114.
The output terminal 106 is connected to the conduction type band-pass filter 34 and to the base of the switching transistor 98 via the resistor 116. Output terminal 1
08 is connected to the conduction band-pass filter 36 and is connected to the switching transistor 1 via the resistor 118.
00 is connected to the base. The output terminal 110 is connected to the conduction band-pass filter 38 and is connected to the resistor 1.
20 is connected to the base of the switching transistor 102.

Therefore, when a DC voltage of + Vc is generated at the output terminal 104, the output signal of the amplifier 26 is supplied to the band-pass filter 32, the switching transistor 96 is turned on, and the variable resistors 88 and 28 are turned on. Flows through the PIN diode 62 via the
Is determined by the values of the variable resistors 88 and 28.

Similarly, when a DC voltage of + Vc is generated at the output terminal 106, the output signal of the amplifier 26 is supplied to the band-pass filter 34, the switching transistor 98 is turned on, and the variable resistor 90, A current flows through the PIN diode 62 through the variable attenuator 24a.
Is determined by the values of the variable resistors 90 and 28.

When a DC voltage of + Vc is generated at the output terminal 108, the output signal of the amplifier 26 is supplied to the band-pass filter 36, the switching transistor 100 is turned on, and the variable resistors 92 and 28 are turned on. Flows through the PIN diode 62 via the
Is determined by the values of the variable resistors 92 and 28.

Similarly, when a DC voltage of + Vc is generated at the output terminal 110, the output signal of the amplifier 26 is supplied to the band-pass filter 38, the switching transistor 102 is turned on, and the variable resistors 94 and 28 are turned on. Current flows through the PIN diode 62 through the
The attenuation of “a” is determined by the values of the variable resistors 94 and 28. Thus, the switch circuit 112 functions as a control unit.

By making the following adjustments at the time of factory shipment, the output level generated at the output terminal 48 can be made constant as shown in FIG. That is, the band-pass filter having the lowest output level, for example, the band-pass filter 36
The variable resistor 92 is adjusted so that the output level becomes maximum in a state where the channel selection unit 18 is adjusted so that the output of the channel selection unit 18 is generated at the output terminal 48. At this time, the variable resistor 28 is adjusted so that its influence becomes zero.

Next, the channel selector 18 is adjusted to
An output signal of the band-pass filter 32 is generated at an output terminal 48. Then, the variable resistor 88 is adjusted so that the output signal of the band-pass filter 32 generated from the output terminal 48 becomes equal to the output level of the band-pass filter 36.

Similarly, the output signal of the band-pass filter 34 is generated at the output terminal 48 by adjusting the channel selection unit 18. Then, the variable resistor 90 is adjusted so that the output signal of the band-pass filter 34 generated from the output terminal 48 becomes equal to the output level of the band-pass filter 36.

Finally, the channel selector 18 is adjusted so that the output signal of the band-pass filter 38 is generated at the output terminal 48. Then, the variable resistor 94 is adjusted so that the output signal of the band-pass filter 38 generated at the output terminal 48 becomes equal to the output level of the band-pass filter 36.

With the effect of the variable resistor 28 reduced to zero,
By adjusting each of the variable resistors 88, 90, 92, 94, each band-pass filter 3 generated at the output terminal 48 is formed.
Since the output levels of 2, 34, 36 and 38 are the same, the output level of any of the band-pass filters 32, 34, 36 and 38 can be adjusted to a desired value only by adjusting the variable resistor 28. By providing a scale of the output level on the variable resistor 28, the output terminal 48
Can be displayed.

In the above embodiment, the number of bandpass filters is four, but the number can be arbitrarily changed as long as the number is two or more. In the above embodiment, the variable attenuator 24a is provided. Alternatively, for example, the amplifying unit 22 or 26 may be configured as a variable gain amplifying unit and the gain may be changed. Further, the variable resistors 28, 8
Instead of 8, 90, 92, 94, transistors and FETs
Can be used, and a switching FET can be used instead of the switching transistors 96, 98, 100, and 102. Further, in the above-described embodiment, the output signal of the amplification unit 26 is converted into each band-pass filter 32,
Although the configuration is such that the signals are supplied to the amplifiers 34, 36, and 38, the output signals of the band-pass filters 32, 34, 36, and 38 may be supplied to the amplifier 22.

[0035]

As described above, according to the present invention, the gain adjustment signal generated by each of the gain adjustment signal generation means can maintain the signal level of the output terminal even when any of the band-pass filter means is activated. Are selected so as to be substantially at predetermined levels, so that the band-pass filter means for passing the frequency of the signal supplied to the input terminal is activated by the filter activation signal from the control means, and The gain adjustment signal generated by the gain adjustment signal generation means which is energized by the gain adjustment energization signal from the control means has a signal level at the output terminal substantially equal to a predetermined level. Therefore, even if an input signal having a different signal level according to the frequency is supplied to the input terminal, the signal level of the output signal output from the output terminal becomes substantially a predetermined level. Even if the frequency changes, the user does not need to readjust the signal level one by one,
Adjustment work can be made unnecessary.

[Brief description of the drawings]

FIG. 1 is a block diagram of one embodiment of a filter device according to the present invention.

FIG. 2 is a frequency-output level characteristic diagram of the embodiment.

FIG. 3 is a block diagram of a frequency variable television modulator using a conventional filter device.

FIG. 4 is a frequency vs. output level characteristic diagram of a conventional filter device.

[Explanation of symbols]

24a Variable attenuator (gain adjusting means) 32 34 36 38 Bandpass filter (bandpass filter means) 88 90 92 94 Variable resistor (gain adjusting signal generating means) 96 98 100 102 Switching transistor (gain adjusting signal generating means) 112 Switch circuit (control means)

Claims (1)

(57) [Claims] 1. An input terminal to which an input signal having a signal level different according to a frequency is supplied, and an output terminal, each having a different pass band, and when a filter energizing signal is supplied, a signal within its own pass band is provided. A plurality of band-pass filter means for extracting the input signal of the frequency of
Filter parallel means connected in parallel; gain adjusting means connected in series with the filter parallel means between the input terminal and the output terminal to adjust a gain to a value according to a gain adjusting signal; Gain adjustment signal generating means for generating the gain adjustment signal when a gain adjustment energizing signal is supplied, provided corresponding to the band-pass filter means, respectively; Control means for simultaneously supplying the filter energizing signal and the gain adjusting energizing signal to the signal generating means, and wherein the gain adjusting signals generated by the respective gain adjusting signal generating means are any of the above Filter devices each selected such that the signal level at the output terminal is substantially at a predetermined level even when the band-pass filter is energized.