JPH046267Y2 - - Google Patents

Description

[Detailed description of the invention] [Field of industrial application] The present invention relates to a tuner input circuit for CATV in which VHF input and UHF input, including each of the low, high and hyper bands, have the same common input terminal. be.

[Conventional technology]

A specific example of a tuner input circuit in which VHF and UHF input tuning sections are connected through the same common input terminal will be shown below with reference to FIG. In the figure, 1 is the common input terminal, 2 is the capacitor C ₁ , C ₂ and the coil
3 consists of resonant lines L _{2 and} L ₃ and a variable capacitance diode VD _1, etc., and is a high-pass filter 2 connected to the common input terminal 1.
The UHF input tuning section connected to the output of 4 consists of capacitor C ₃ and coil L ₄ , and the common input terminal
5 is an IF filter connected to the output of low-pass filter 4, SD ₁ is an IF filter whose cathode is connected to the output of IF filter 5 through a parallel connection of capacitor C ₄ and resistor R ₁ . 1 switching diode, 6 capacitor C ₅ and coil L ₅ ,
A hyperband circuit consisting of L ₆ , L _7, etc., connected to the anode of the first switching diode SD ₁ .
VHF input tuning section, 7 is a power supply terminal for applying switching voltage of the first switching diode SD ₁ ;
SD ₂ is connected through the parallel connection of capacitor C ₄ and resistor R ₁
A second switching diode whose cathode is connected to the output of the IF filter 5 in parallel with the first switching diode SD ₁ ; 8 is a coil L ₈ , L ₉ , L ₁₀ ,
It consists of _L11 , _L12 , capacitor _C6 , switching diode _SD10, etc., and is connected to the anode of the second switching diode _SD2 .
This is a VHF input tuning section.

In the above configuration, when a continuous signal from VHF to UHF is received at common input terminal 1, the UHF signal is selected and separated by high-pass filter 2.
The signal is input to the UHF input tuning section 3. Further, the VHF signal including the hyperband is selected by a low-pass filter 4, and the interfering signal is removed by an IF filter 5. 8 is input.

Then, during hyperband reception, a switching voltage is applied from the power supply terminal 7 to the first switching diode _SD1 . Then, the first switching diode SD ₁ becomes forward biased and conducts, and the second switching diode SD ₂ becomes reverse biased and is cut off in terms of direct current, and the tuning section 6
VHF signal is input. On the other hand, a switching voltage is applied from the power supply terminal 9 to make the switching diode SD ₁₁ conductive and ground the capacitor C ₇ .
Coils _L9 , _L10, etc. are short-circuited at high frequency to eliminate interference.

Furthermore, when a switching voltage is applied from the coil L ₁₀ side during VHF low band reception, the second switching diode SD ₂ becomes conductive, and the first switching diode SD ₁ cuts off the DC current, and the coils L ₉ and L ₁₀ , L ₁₁ , L ₁₂ and the like. Furthermore, when receiving VHF Hanband, a switching diode SD ₁₀ is used.
When a switching voltage is applied from the anode side of the switch, the switching diode SD ₁₀ and the second switching diode SD ₂ become conductive, and the first switching diode SD ₁ is cut off in terms of direct current, and the coils L ₁₀ , L ₁₂ and the capacitor A signal is input to a tuning section 8 formed by C6 or _the like.

[The problem that the idea aims to solve]

By the way, in the tuner input circuit described above, each VHF and UHF input tuning section 3, 6, 8 is connected to one common input terminal 1 via low-pass and high-pass filters 4, 2, and each input are input after being separated by a filter. However, VHF
is between the high frequency side of the hyperband and UHF, e.g.
Since the high band is included between 300 and 360 MHz to about 500 MHz, the reception channel is almost continuous from the low band of VHF to UHF. Therefore, unless the cutoff frequency of the low-pass filter 4 is set higher than the hyperband, the hyper component of VHF will be attenuated, and if it is set too high, the UHF will be attenuated. In addition, absorption traps are generated in the hyperband due to resonance between the coil and capacitor of high-pass filter 2, and as a result, mutual interference occurs between the UHF and VHF hyperbands, and their respective signals are attenuated. Put it away.

[Means to solve the problem]

In the present invention, a VHF input tuning section and a UHF input tuning section including low, high, and hyper bands are connected to the same common input terminal through a low-pass filter and a high-pass filter, respectively, and In a tuner input circuit that switches each input by interposing first and second switching diodes at each input end of the VHF input tuning section for each of the hyper, low, and high bands, the common input terminal and the high frequency UHF between passing filter
a third switching diode for switching whether or not the input is connected; a fourth switching diode located within the high-pass filter for switching whether or not to operate; and a fourth switching diode located within the low-pass filter for switching the cut-off frequency. A fifth switching diode and a sixth switching diode for applying a forward bias to the first switching diode during UHF reception are provided.

[Effect]

According to the above technical means, when receiving UHF, the third and fourth switching diodes are made conductive to operate the high-pass filter, and the fifth switching diode is made conductive to operate the cut-off frequency of the low-pass filter. At the same time, a forward bias is applied from the sixth switching diode to the first switching diode to make it conductive, thereby eliminating the series resonance of the VHF hyperband input circuit. vice versa,
When receiving VHF, the third and fifth switching diodes are turned off to cut off the high-pass filter in a DC manner, and the cut-off frequency of the low-pass filter is increased.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. In the figure, 11 is a common input terminal, 12 is a high-pass filter consisting of capacitors C ₁ and C ₂ and coil L ₁ , and SD ₃ is between the common input terminal 11 and the high-pass filter 12, and connects both. 3rd switching diode, SD ₄ is high pass filter 1
2 is a fourth switching diode that switches whether or not coil L ₁ is connected; 13 is a resonant line;
Consists of L ₂ , L ₃ and variable capacitance diode VD ₁ , etc.
UHF input tuning circuit connected to the output of high-pass filter 12, 14 is capacitor C ₃ , C ₈ and coil
_L4 is a low-pass filter connected to the common input terminal 11, and _SD5 is a fifth switching diode in the low-pass filter 14 that switches the cut-off frequency high or low by switching whether or not the capacitor _C8 is connected. , 15 is an IF filter connected to the output of the low-pass filter 14, SD ₁ is a first switching diode whose cathode is connected to the output of the IF filter 15 through a parallel connection of a capacitor C ₄ and a resistor R ₁ , and 16 is an IF filter connected to the output of the low-pass filter 14. a hyperband input tuning circuit consisting of a capacitor C ₅ and coils L ₅ , L ₆ , L _7, etc., connected to the anode of the first switching diode SD ₁ ;
SD ₆ is the sixth switching diode that applies forward bias to the first switching diode SD ₁ during UHF reception, and SD ₇ is the sixth switching diode that applies forward bias to the first switching diode SD 1 during hyperband reception.
A seventh switching diode, _SD2 , which applies a forward bias to the switching diode _SD1 , is connected in parallel to the first switching diode _SD1 to the output of the IF filter 15 through a parallel connection of a capacitor _C4 and a resistor _R1 . The second switching diode with the cathode connected, 18 is the coil L ₈ , L ₉ , L ₁₀ , L ₁₁ , L _{12
UB 1 , UB 2 , UB 3 are UHF} Each power supply terminal for applying switching voltage during reception,
BHY ₁ , BHY ₂ , BHY ₃ are power supply terminals for applying switching voltage during hyperband reception, BL,
BH is each power supply terminal for applying switching voltage during VHF low and high band reception, _R2 is
3rd and 5th switching diodes when receiving VHF low, high, and hyper bands
A resistor 19 is a high frequency blocking coil for applying a reverse bias to SD ₃ and SD ₅ .

The operation of the present invention in the above configuration will be described below. First, when a continuous signal from VHF to UHF is received at the common input terminal 11, switching voltage is supplied from the power terminals UB ₁ , UB ₂ , and UB ₃ during UHF reception. Then, the third and fourth switching diodes SD ₃ and SD ₄ become conductive, and the high-pass filter 12 and the common input terminal 11 become conductive.
The second switching diode SD ₂ is cut off in terms of direct current, and the fifth switching diode SD ₅ is conductive to short-circuit capacitors C ₃ and C ₈ , making the cut-off frequency of the low-pass filter 14 sufficiently lower than UHF. Become. Also, the sixth switching diode _SD1 conducts the first switching diode _SD6 ,
This removes UHF signal traps caused by the capacitance (approximately 0.8PF) during reverse bias and the series resonance of coils L ₅ and L ₆ .

Therefore, the UHF signal among the continuous signals is passed through the high-pass filter 12 without its low frequency being interfered with by the low-pass filter 14 or trapped by the hyperband input tuning circuit 16. The signal is input to the UHF input tuning circuit 13 through
Its receiving sensitivity is improved.

Next, when receiving VHF hyperband, a switching voltage is first supplied from the power supply terminal BHY ₁ . Then, the switching diode SD ₇ ,
SD ₁ becomes forward biased, and the third and fifth switching diodes SD ₃ and SD ₅ become reverse biased via the second switching diode SD ₂ and resistor R ₂ .
Therefore, the high-pass filter 12 and the VHF input tuning circuit 18 are DC-cut from the common input terminal 11, and the capacitors _C3 and _C8 in the low-pass filter 14 are DC-cut to increase the cut-off frequency. Keep it high enough for the band. Therefore,
Among the signals received at the common input terminal 11, VHF
The signal passes through the low-pass filter 14 and the IF filter 15 without being attenuated in the hyperband and is input to the hyper input tuning circuit 16. At this time, a forward bias is applied to the switching diodes SD ₁₀ and SD ₁₁ from the power supply terminals BHY ₂ and BHY ₃ to prevent interference from the VHF input tuning circuit 18.

Also, when receiving VHF low band, power terminal BL
Supplies switching voltage to Then, the second switching diode SD ₂ becomes forward biased and conductive, and the first, third, and fifth switching diodes SD ₁ , SD ₃ , and SD ₅ become reverse biased. Therefore, the high-pass filter 12 and the hyper input tuning circuit 16 are DC-cut from the common input terminal 11, and the capacitors _C3 and _C8 in the low-pass filter 14 are DC-cut to set the cut-off frequency to VHF. Keep it high enough for . Therefore,
Among the signals received at the common input terminal 11, VHF
The signal passes through the low-pass filter 14 without attenuation in the VHF band, and further passes through the IF filter 15, and is then connected to coils L ₉ , L ₁₀ , L ₁₁ , L ₁₂ and capacitors C ₉ ,
The signal is input to a UHF input tuning circuit 18 consisting of C ₁₀ , C ₁₁ and the like. Furthermore, when receiving VHF high band, a switching voltage is applied to the power supply terminal BH. Then, the switching diodes SD ₁₀ and SD ₂ become forward biased and conductive, and the first, third, and fifth switching diodes SD ₁ , SD ₃ ,
SD ₅ is reverse biased. Therefore, the high-pass filter 12 and the VHF input tuning circuit 16 are DC-cut from the common input terminal 11, and the capacitors _C3 and _C8 in the low-pass filter 14 are DC-cut to set the cut-off frequency to VHF. Keep it high enough. Therefore, among the signals received at the common input terminal 11, the VHF signal passes through the low-pass filter 14 and further through the IF filter 15 without being attenuated in the VHF band, and then passes through the coils L ₁₀ and L ₁₂ and the capacitor C. VHF input tuning circuit 1 formed by ₁₁ etc.
8 is input.

[Effect of idea]

According to the present invention, in a tuner input circuit that inputs VHF and UHF signals from the same common input terminal through low-pass and high-pass filters, each input tuning circuit is switched according to each receiving band, and Since the cutoff frequency of the filter is switched, it is possible to reduce mutual interference in each input tuning circuit when UHF and VHF signals are input, and it is possible to increase UHF reception sensitivity and improve characteristics.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of a tuner input circuit according to the present invention, and FIG. 2 is a circuit diagram showing a specific example of a conventional tuner input circuit. 11... Common input terminal, 12... High pass filter, 13... UHF input tuning circuit, 14... Low pass filter, 16, 18... VHF input tuning circuit, SD ₁ , SD ₂ , SD ₃ , _SD4 , _SD5 , _SD6 ...first, second, third, fourth, fifth, and sixth switching diodes.

Claims (1)

[Claims for Utility Model Registration] Each input tuning section of the UHF band and the VHF band including each of the low, high and hyper bands is connected to the common input terminal via a high-pass filter or a low-pass filter, respectively; In an input circuit that switches between a hyperband input tuning circuit and a low and high band input tuning circuit with first and second switching diodes interposed, the UHF input terminal is located between the common input terminal and the high-pass filter. a third switching diode for switching connection/non-connection of the filter; a fourth switching diode located within the high-pass filter for switching its operation/non-operation; and a fourth switching diode located within the low-pass filter for switching its cut-off frequency from high to low. 1. A tuner input circuit comprising: a fifth switching diode; and a sixth switching diode that applies a forward bias to the first switching diode during UHF reception.