JP2000151272A - Tuner for cable modem - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tuner for a cable modem which exerts characteristics improvement. SOLUTION: In this tuner for a cable modem, a broadband amplifier circuit 21 is inserted to an input circuit side of RF amplifiers 6 and 8. The circuit 21 operates as a buffer amplifier. Therefore, an input tuning characteristics in RF amplification input tuning circuits 3 to 5 is not generated in the inputting state of a tuner, the input impedance characteristics of the circuit 21 reflects input return loss as it is, and the input return loss is reduced drastically. Also, isolation is obtained by the circuit 21, and local leakage mainly with the leakage of oscillation signals of local oscillation circuits 10 and 14 in a tuner inputting stage as main parts is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a tuner for a cable modem, and more particularly, to a tuner for a cable modem having an improved characteristic level.

[0002]

2. Description of the Related Art In CATV, HFCs (abbreviation of Hybrid Fiber / Coax) adopting a coaxial cable as a service line for each home and an optical fiber cable as a trunk line are being introduced.

[0003] The HFC is adopted to provide a broadband data communication service of several Mbit / s to each home. H
If FC is used, 64QAM (quadratur amplitud modul
) can provide a high-speed data line having a bandwidth of 6 MHz and a transmission speed of 30 Mbit / sec.

By using a cable modem for the high-speed data line, high-speed data communication of 4 Mbit / sec to 27 Mbit / sec using a free channel of CATV is realized. The above-mentioned cable modem has a tuner, and the tuner for the cable modem is 470-86MH.
UHF band with z (B3 band), 170-47
VHF High band (B2 band) with 0 MHz and VHF Low with 54-170 MHz
A receiving circuit is provided for each band (B1 band). However, band division is not specified here.

FIG. 16 is a block diagram of a conventional cable modem tuner. In FIG. 16, a conventional tuner for a cable modem includes an input terminal 1, an HPF (abbreviation for high-pass filter) 2, an upstream circuit 40, a data terminal 41, and a UHF signal for connecting a cable line (not shown) for communication with the tuner. Input switching circuits 19 and 20 for switching between a signal and a VHF signal and inputting the received signal to a predetermined level in accordance with an AGC (automatic gain control) voltage applied from terminal 30 via resistors 31 and 33. High frequency for amplification and output (hereinafter, RF
Amplifiers 6 and 8, RF amplification input tuning circuits 3 to 5 provided in the input stages of RF amplifiers 6 and 8, RF amplification output tuning circuits 16 to 18 also provided in the output stage,
Mixing circuits 9 and 13, local oscillator circuits 10 and 14,
IF (short for intermediate frequency) amplifier circuit 42 and output terminal 15
including.

The CATV signal includes an upstream signal transmitted from the cable modem tuner to the cable line via the terminal 1 and a downstream signal received from the cable line to the cable modem tuner via the terminal 1. Up signal is 5-4
The downstream signal is operated at 2 MHz and the downstream signal is operated at 54 to 860 MHz.

The upstream signal includes a quadrature phase displacement modulated data signal supplied to a data terminal 41 from a QPSK (quadrature phase displacement modulation) transmitter (not shown). The data signal is sent to the cable line via the terminal 41, the upstream circuit 40 and the input terminal 1.

The downstream signal received from terminal 1 is HPF (I
F filter 2), and is supplied to input switching circuits 19 and 20 where the subsequent UHF BAND, VHF
HIGH BAND and VHF LOW BAND
And is output after being switched to any one of the receiving circuits.

The HPF 2 is a filter having an attenuation band of 5 to 46 MHz and a pass band of 54 MHz or more. Only the receiving circuit corresponding to the desired receiving channel among the receiving circuits of each band is in the operating state, and the receiving circuits of the other bands do not operate.

Next, an operation state of the receiving circuit of each band will be described. The downstream signal passes through the input switching circuits 19 and 20, and is applied to any one of the RF amplification input tuning circuits 3 to 5. Here, the signal is tuned to a predetermined signal corresponding to the desired reception channel, output, and amplified in one of the RF amplifiers 6 and 8. Then, the RF amplification output tuning circuit 1
In any one of 6 to 18, the signal is output again in synchronization with the predetermined signal and supplied to one of the mixing circuits 9 and 13.

A signal output from any one of RF amplification output tuning circuits 16 to 18 is supplied to a corresponding one of mixing circuits 9 and 13 by a corresponding one of local oscillation circuits 10 and 1.
4, and is converted into an IF signal, and output to the IF amplifier circuit 42. IF amplifier circuit 4
In 2, the IF signal is amplified and output via the output terminal 15.

As described above, the local oscillation circuit 10 and the mixing circuit 9 and the local oscillation circuit 14 and the mixing circuit 1
Each of 3 is a frequency converter for converting an RF signal into an IF signal corresponding to a desired reception channel. Each of local oscillation circuits 10 and 14 oscillates at a frequency corresponding to the desired reception channel when a tuning voltage + VT corresponding to the desired reception channel is applied.

[0013]

In recent years, it has been desired to improve a characteristic level related to a tuner which is a front end of a cable modem. For example, cable modems for North America are about to establish the standard of multimedia cable network system (MCNS), and it is desired to improve the input return loss and spurious emissions associated with the cable modem tuner.

FIG. 17 is a graph showing the relationship between the reception frequency and the input return loss at the input terminal 1 of FIG. In FIG. 17, the vertical axis represents the input return loss (d
B) is taken, and the receivable frequency (MHz) is taken on the horizontal axis.

In FIG. 16, the RF amplification input tuning circuits 3 to 5 are connected to the input terminal 1 through input switching circuits 19 and 20 and HPF2. Therefore, the input impedance viewed from the input terminal 1 side becomes the tuning characteristics of the RF amplification input tuning circuits 3 to 5 as they are. Therefore, as shown in FIG. 17, for example, at the reception frequency fp, the input return loss at the input terminal 1 is low, and it has been difficult to sufficiently secure the input return loss. In addition, it is impossible to compensate for the input return loss over the entire receiving band.

Further, the spurious emission mainly composed of the local oscillation by the local oscillation circuits 10 and 14 is R
F amplification output tuning circuits 16 to 18, RF amplification circuits 6 and 8,
RF amplification input tuning circuits 3 to 5, input switching circuits 19 and 2
0, and -1 at input terminal 1 via HPF2.
0 dBmV to -30 dBmV is detected. For this reason, noise is mixed into the received signal at the input terminal 1 and hinders a preferable tuning operation. Therefore, for example, MC
NS: -40dBm for spurious emissions
Improvements up to V are required.

An object of the present invention is therefore to provide a tuner for a cable modem with improved characteristics.

[0018]

According to a first aspect of the present invention, there is provided a cable modem tuner for receiving and inputting a CATV signal, extracting and outputting a high frequency signal, and receiving at least two or more reception bands of the CATV signal. Amplification tuning units that are provided for each of the above, input and amplify a signal given from the input unit side, amplify and tune and output the signals, and signals provided corresponding to each of the amplification tuning units and output from the amplification tuning unit And a frequency conversion unit for converting the signal into an intermediate frequency signal corresponding to a desired channel according to a predetermined signal given by input and outputting the intermediate frequency signal, and further comprising a buffer unit.

The buffer section is provided between the input section and the amplification tuning section, receives and processes the high-frequency signal output from the input section, and outputs the processed signal to the amplification tuning section. In this case, the buffer unit is provided to reduce coupling between the input unit and the amplification tuning unit.

According to the first aspect of the present invention, the input section and the amplification tuning section are loosely coupled by the buffer section, so that the tuning characteristic of the amplification tuning section does not occur in the input section, and the input return loss is improved accordingly. The reception quality is improved.

Further, since the buffer unit provides isolation between the input unit and the amplification tuning unit and the frequency conversion unit, local leakage from the amplification tuning unit and the frequency conversion unit in the input unit is reduced, and the reception quality is reduced. Is good.

According to a second aspect of the present invention, in the tuner for a cable modem according to the first aspect, the buffer unit receives the high frequency signal output from the input unit, amplifies the signal over a wide band, and outputs the amplified signal. It is configured to include an amplification unit.

According to claim 2, the buffer unit has a wide band C
Since a wide-band amplifier serving as a buffer that performs an amplification operation on the ATV signal is included, the input impedance characteristic of the wide-band amplifier at the input unit becomes the input return loss. As a result, the input return loss at the input section is improved and the reception quality is improved.

In addition, since the isolation between the input section, the amplification tuning section and the frequency conversion section can be obtained by the wide band amplification section, local leakage from the amplification tuning section and the frequency conversion section in the input section is reduced and the reception quality is reduced. Is good.

According to a third aspect of the present invention, there is provided a cable modem tuner according to the second aspect, wherein the broadband amplifier in the cable modem tuner of the second aspect includes a broadband amplifier circuit connected in one or more stages.

According to the third aspect of the present invention, the wideband amplifier is constructed by connecting a wideband amplifier circuit to one or more stages, so that the input return loss and the local leakage can be improved.

According to a fourth aspect of the present invention, there is provided a cable modem tuner according to the second aspect, wherein the broadband amplifying unit in the cable modem tuner according to the second aspect includes a balanced amplifying unit comprising two broadband amplifying circuits connected in complementary symmetry. Is done.

According to the fourth aspect of the present invention, the broadband amplifier is constituted by a balanced amplifier in which the broadband amplifiers are connected in a complementary symmetric manner, so that the input return loss and the local leakage can be reduced.

According to a fifth aspect of the present invention, there is provided a cable modem tuner according to the fourth aspect, wherein the broadband amplifier is provided with a balun circuit at each of an input stage and an output stage of the balanced amplifier. .

According to the fifth aspect, the balun circuit is provided at each of the input stage and the output stage of the balanced amplifying unit, thereby further promoting the isolation between the input unit and the amplification tuning unit and the frequency conversion unit. As a result, local leakage at the input unit is further reduced, and the reception quality is improved.

According to a sixth aspect of the present invention, there is provided a tuner for a cable modem according to any one of the second to fifth aspects, wherein the buffer unit is provided at an output stage of the wideband amplifying unit. It further includes a signal distribution unit that inputs a signal and distributes the signal to each of the amplification tuning units.

According to the sixth aspect of the present invention, since the signal distribution unit is provided, the input unit is further isolated from the amplification tuning unit and the frequency conversion unit, so that the local leakage at the input unit is further reduced. The reception quality is improved.

According to a seventh aspect of the present invention, there is provided a tuner for a cable modem according to any one of the second to fifth aspects, wherein the buffer unit is provided at an input stage of the wide-band amplifying unit. , And a filter unit for extracting a signal of a desired band and outputting the extracted signal to a wideband amplifying unit.

According to the seventh aspect, the filter unit outputs only the signal of the desired band among the high-frequency signals output from the input unit to the circuit units of the next and subsequent stages. Is not given to the circuit section of FIG. As a result, the local tuning from the amplification tuning unit and the frequency conversion unit in the input unit is reduced, and the reception quality is improved.

According to an eighth aspect of the present invention, there is provided a cable modem tuner according to the seventh aspect, wherein the filter section of the cable modem tuner according to the seventh aspect is a low-pass filter whose cutoff frequency is variably set in accordance with a given signal. You.

According to the eighth aspect, since the cutoff frequency of the low-pass filter can be variably set in accordance with a given signal, only a signal in a desired band can be easily supplied to the circuit units in the next and subsequent stages. As a result, as described above, local leakage at the input unit can be reduced as desired, and reception quality can be improved.

According to a ninth aspect of the present invention, there is provided a tuner for a cable modem according to the seventh aspect, wherein the filter section of the tuner for the cable modem according to the seventh aspect cuts off according to a desired reception band among at least two or more reception bands. It is configured to be a low-pass filter whose frequency is variably set.

According to the ninth aspect, the cut-off frequency of the low-pass filter can be variably set in accordance with a desired band among a plurality of reception bands of the CATV signal. Circuit section. As a result, as described above, local leakage in the input unit can be reduced as desired, and reception quality can be improved.

According to a tenth aspect of the present invention, there is provided a tuner for a cable modem according to any one of the second to fifth aspects, wherein the buffer unit is provided in one of an input stage and an output stage of the wideband amplifying unit. The attenuator further includes a damping unit.

When the attenuator is provided at the input stage of the wide-band amplifier, the high-frequency signal output from the input is input to the attenuator to control the frequency band other than the frequency band to be adjusted by the amplifier tuning unit and the frequency converter. Is attenuated and output to the broadband amplifier. Also, when provided at the output stage of the broadband amplifier, a signal output from the broadband amplifier is input, and the signals other than the frequency band to be adjusted are attenuated by the amplification tuning unit and the frequency converter. Output to the amplification tuning section.

According to the tenth aspect, the signal other than the frequency band to be adjusted in the input / output stage of the wideband amplifying unit, that is, the local leakage is effectively attenuated by the attenuating unit, and the reception quality is improved. .

A cable modem tuner according to a eleventh aspect of the present invention provides a cable modem tuner according to the tenth aspect, wherein the frequency conversion unit oscillates at a frequency according to a predetermined signal, and a signal output from the amplification tuning unit. And a mixing circuit that mixes the oscillation signal of the local oscillation circuit and outputs an intermediate frequency signal. The attenuator includes a trap circuit tuned to the oscillation frequency of the local oscillation circuit.

According to the eleventh aspect, the trap circuit operates while being tuned to the oscillation frequency of the local oscillation circuit, and acts so as to attenuate local leakage caused by the local oscillation circuit. Therefore, local leakage mainly due to signal leakage due to the local oscillation circuit in the input unit is effectively attenuated, and the reception quality is improved.

[0044]

Embodiments of the present invention will be described below with reference to the drawings. The value of each circuit described later is a reference value, not a guaranteed value.

[First Embodiment] FIG. 1 is a block diagram according to a first embodiment of the present invention. The configuration of the tuner for the cable modem shown in FIG. 1 is different from the conventional one shown in FIG. 16 in that a broadband amplifier 21 for amplifying a CATV signal which is a wideband signal is added between the HPF 2 and the input switching circuits 19 and 20. Is that Other configurations are the same as those in FIG. 16 and the description is omitted.

FIG. 2 is a graph showing the relationship between the reception frequency and the input return loss at the input terminal 1 of FIG. In FIG. 2, the vertical axis represents the input return loss (dB), and the horizontal axis represents the receivable frequency (MHz).

Since broadband amplifier circuit 21 is provided in series between input switching circuits 19 and 20 and HPF2, broadband amplifier circuit 21 operates as a buffer amplifier, and a circuit group on HPF2 side and input switching circuit are provided. 19 and 20
The coupling with the subsequent circuit group is loosened, and the tuning characteristics of the RF amplification input tuning circuits 3 to 5 are not detected at the input terminal 1.
In other words, the input impedance characteristic (input return loss) seen from the input terminal 1 side becomes the input impedance characteristic of the broadband amplifier circuit 21, and as shown in FIG. The input return loss can be greatly improved as compared with the prior art.

Here, the rejection ratio of input / output signals, that is, isolation, will be considered. In the case of FIG. 1, the isolation by the broadband amplifier circuit 21 indicates the attenuation ratio (rejection ratio) of the signal output from the input terminal when the signal is applied from the output terminal of the broadband amplifier circuit 21. According to the broadband amplifier circuit 21, this attenuation ratio is extremely high.

As described above, according to the wide-band amplifier circuit 21, the isolation can be obtained effectively, so that the input terminal 1
Local leakage due to the local oscillation circuits 10 and 14 on the side is sufficiently attenuated by the broadband amplifier circuit 21 to improve reception quality. Therefore, spurious emissions on the side of the RF amplification input tuning circuits 3 to 5 are sufficiently reduced, and a good tuning operation can be obtained.

Hereinafter, a configuration example of the broadband amplifier circuit 21 according to the first embodiment of FIG. 1 will be described with reference to the following first to third embodiments.

(Embodiment 1) FIG. 3 is a block diagram of a broadband amplifier circuit according to Embodiment 1 of the present invention. 3 includes DC blocking capacitors C1 and C3, a matching inductor L1 for impedance matching, an amplifier circuit 1A, and an attenuation circuit 211.

The amplifier circuit 1A is connected in series to the output stage of the HPF 2 via the DC blocking capacitor C1 and the matching inductor L1, and the attenuation circuit 211 is connected to the broadband amplifier circuit 21A.
Circuit 1 via the DC blocking capacitor C3 to the output stage of
A is connected in series.

The amplifier circuit 1A includes a MOSFET (Metal Oxid
e Semiconductor Field Effect Transistor) amplifying element Q1 and bypass capacitors C4 and C5 for grounding the source electrode of amplifying element Q1 and bias resistor R1, voltage feedback connecting drain electrode and gate electrode of amplifying element Q1. Path, terminal T to amplifying element Q1
1 includes a ground bypass capacitor C6 for stably supplying the power supply voltage + B from 1 and a choke coil L2 which is a high-frequency inductor.

The aforementioned voltage feedback path includes a DC blocking capacitor C2, bias resistors R2 and R4, and a resistor R3 for voltage feedback. The aforementioned attenuating circuit 211 has a resistor R
5 to R7.

In this case, the DC blocking capacitor is used so that the DC voltage of the preceding circuit is not applied to the input of the next circuit, and the two circuits are AC-coupled. A matching inductor or matching capacitor is used to match the impedance at one end with the impedance at the other end.

In operation, the input terminal 1 and the HPF 2
The downstream CATV signal that has passed through
1 and the matching inductor L1 to the gate electrode of the amplification element Q1 in the amplification circuit 1A.

The amplifying element Q1 has a choke coil L
2 and the power supply voltage + B via the bypass capacitor C6.
Is supplied to set a DC bias via bias resistors R1, R2 and R4.

C given to the gate electrode of amplifying element Q1
The ATV signal is amplified through a voltage feedback path, and then divided by an attenuating circuit 211, which is an output side load, and a voltage feedback resistor R3, and supplied to input switching circuits 19 and 20 at the next stage.

In the wide-band amplifier 21 shown in FIG. 3, -4 dB is obtained in the attenuation circuit 211 with respect to the gain.
The amplifier circuit 1A is designed so that a gain of 5 to 6 dB is obtained and a gain of 1 to 2 dB is finally obtained.

More specifically, in FIG.
~ C6 is 1000pF ~ 10000pF, resistance R1 is 4
7Ω, resistor R2 is 120 kΩ, resistor R4 is 270 kΩ,
The resistor R3 has a value of 330Ω, the resistors R5 and R6 have a value of 220Ω, the resistor R7 has a value of 24Ω, the inductor L1 has a value of 6.8 nH, and the coil L2 has a value of 1 μH.

(Embodiment 2) FIG. 4 is a block diagram of a broadband amplifier circuit according to Embodiment 2 in Embodiment 1 of the present invention. 1 may have the configuration shown in FIG. In the broadband amplifier circuit 21B of FIG. 4, the amplifier element Q1 of FIG. 3 is replaced by an amplifier element Q11 which is a bipolar transistor. The other configuration of the broadband amplifier circuit 21B except for the amplifying element Q11 is the same as that of FIG.

The value of each element in FIG.
Has 7Ω. The values of the other elements are the same as those in FIG.

Note that the amplifying element Q1
In the case where an amplifying element which is a bipolar transistor as described in 1 is adopted, it is necessary to pay attention to heat generation because a current supply of several tens mA is always required to the base electrode of the transistor. It is also necessary to pay attention to the deterioration of the intermodulation distortion.

The wide band amplifier circuits 21A and 21B shown in FIGS. 3 and 4 have the same performance and can improve the input return loss and the local leakage.

(Embodiment 3) FIG. 5 is a block diagram of a broadband amplifier circuit according to Embodiment 3 in Embodiment 1 of the present invention. 1 may be configured as shown in FIG.

In FIG. 5, a wide-band amplifier circuit 21C is composed of a multi-stage cascade-connected amplifier circuit 1A shown in FIG. 3 and an amplifier circuit 1C formed by a bipolar transistor amplifying element Q2 similar to that shown in FIG. It includes an amplification circuit and the above-described attenuation circuit 211 connected to the output side of the multi-stage amplification circuit via a DC blocking capacitor C9. In the broadband amplifier circuit 21C, a gain is obtained by an amplification operation by a combination of the amplification elements Q1 and Q2. The number of connection stages of the multistage amplifier circuit is 2
It is not limited to steps.

An amplifier circuit 1C is connected to the output stage of the amplifier circuit 1A via a DC blocking capacitor C3.

The power supply voltage + B is supplied to the amplifying element Q2 from the terminal T1 via the choke coil L3 and the bypass capacitor C8, similarly to the amplifying element Q1. Further, a DC bias is supplied to the amplifier element Q2 via bias resistors R10 and R9.

In operation, the input terminal 1 and the HPF 2
Is applied to the gate electrode of the amplifier element Q1 via the DC blocking capacitor C1 and the matching inductor L1.

After the signal supplied to the amplifier Q1 is amplified, the signal is divided by the load on the output side of the amplifier Q1 and the voltage feedback resistor R3 and output.

The output signal on the load side of the amplifying element Q1 is applied to the base electrode of the next-stage amplifying element Q2 via the DC blocking capacitor C3. The signal supplied from the amplifier Q2 is amplified in the same manner as the amplifier Q1 in the previous stage,
The signal is output to the attenuation circuit 211.

The bias resistor R10 is connected to the amplifying element Q2
At the same time as the current feedback resistor, which acts to reduce distortion. Further, the bias resistor R10
Is used in combination with the voltage feedback resistor R8 to determine the gain for the amplifying operation in the amplifying element Q2.

In the broadband amplifier circuit 21C shown in FIG. 5, a gain of 8 to 10 dB is obtained in the amplifier circuit including the amplifying elements Q1 and Q2, and a gain of -4 dB is obtained in the attenuation circuit 211. As a result, 4 to 6 dB is obtained. It is designed to gain.

Specifically, the capacitors C1 to C9 are 10
00 to 10000 pF, coil L1 is 6.8 nH, coils L2 and L3 are 1 μH, resistor R1 is 47Ω, resistor R2 is 120 kΩ, resistor R3 is 330Ω, and resistor R4 is 270 k.
Ω, resistors R5 and R6 are 220Ω, resistor R7 is 24Ω, resistor R8 is 330Ω, resistor R9 is 18 kΩ, and resistor R
10 has a value of 47Ω.

[Second Embodiment] FIG. 6 is a block diagram of a tuner for a cable modem according to a second embodiment of the present invention.

The configuration of the tuner for the cable modem shown in FIG. 6 differs from that shown in FIG. 1 in that a signal distribution circuit 22 is provided between a broadband amplifier circuit 21 and input switching circuits 19 and 20.
Is added. The other configuration of FIG. 6 is the same as that of FIG.

In FIG. 6, the use of the broadband amplifier circuit 21 and the signal distribution circuit 22 particularly improves local leakage.

FIG. 1 in which only the broadband amplifier circuit 21 is employed.
In the case of (1), an isolation of 15 to 20 dB is obtained, but in the case of FIG. 6, about 20 to 25 dB is obtained.

An example of the circuit configuration of the broadband amplifier circuit 21 and the signal distribution circuit 22 shown in FIG. 6 is shown in the following first and second embodiments.

(Embodiment 1) FIG. 7 is a block diagram of a broadband amplifier circuit and a signal distribution circuit according to Embodiment 1 of the second embodiment of the present invention.

The signal distribution circuit 22A as a load circuit is connected to the output stage of the broadband amplifier circuit 21D of FIG. This further improves the isolation.

The broadband amplifier 21D includes an amplifier 1D connected to the output stage of the HPF 2 via the DC blocking capacitor C1 and the matching inductor L1. Amplifier circuit 1D
2 is different from the amplifier circuit 1A of FIG. 2 in that the choke coil L2 of the amplifier circuit 1A is replaced with a coil L21. The other configuration of the amplifier circuit 1D is the amplifier circuit 1A
The description is omitted.

The signal distribution circuit 22A includes a coil L21, a DC blocking capacitor C3, a matching capacitor C7, a bias resistor R5, and a circuit for outputting a signal to one of the input switching circuits 19 and 20. This circuit includes a null resistor R6 connected in parallel to a coil L3, signal switching diodes D1 and D2, DC blocking capacitors C8 and C9 connected in series to each of the signal switching diodes D1 and D2, a signal switching diode D1 and Includes bias resistors R7 and R8 for D2, and terminals T2 and T3. A predetermined voltage is applied to one of terminals T2 and T3. Specifically, the terminal T3 has + VB when the VHF band circuit operates, and the terminal T2
Is applied with a voltage of + UB when the UHF band circuit operates.

In operation, the output signal of the amplifier circuit 1D is output from the coil L21 and applied to the coil L3 via the DC blocking capacitor C3 and the matching capacitor C7. The signal applied to the coil L3 is distributed to the paths on the diode D1 side and the diode D2 side. Terminal T3
When voltage + UB is supplied, the signal is applied to input switching circuit 19 via diode D1 and DC blocking capacitor C8. On the other hand, the voltage + VB
Is supplied to the input switching circuit 20 via the diode D2 and the DC blocking capacitor C9.

In the above operation, the coils L21 and L21
3 form a balun circuit, so that a signal distribution circuit including a balanced circuit including two circuits having different characteristic impedances (amplifying circuit 21D and a line to input switching circuit 19 and a line to input switching circuit 20). 22
Even if A) is connected, it is reflected at the connection point.
on) does not occur, and the local leakage is satisfactorily improved.

The circuit formed by the coils L21 and L3 is a matching balun circuit for impedance matching or a two-distribution balun circuit.

In the circuit of FIG. 7, the capacitor C7 is 1
３3 pF, resistor R6 is 150Ω, resistors R5, R7 and R8 are 1.5 kΩ, and capacitors C8 and C9 are 1
000 pF. The values of the other elements are the same as those in FIG.

(Embodiment 2) FIG. 8 is a block diagram of a broadband amplifier circuit and a signal distribution circuit according to Embodiment 2 of the present invention. The wideband amplifier circuit 21 and the signal distribution circuit 22 shown in FIG. 6 may be configured by a wideband amplifier circuit 21E and a signal distribution circuit 22B as shown in FIG.

In FIG. 8, the output stage of the HPF 2 includes a DC blocking capacitor C1 and a balance-unbalance conversion transformer L3.
1, a broadband amplifier circuit 21E including an amplifier circuit 1E is connected.

The amplification circuit 1E includes amplification elements Q1 and Q2
Is a balanced amplifying circuit in which two amplifying circuits 1D of FIG.
2 is the same as that of FIG.

The output stage of the amplifier circuit 1E includes a transformer L22 for impedance conversion which is a load of the amplifier elements Q1 and Q2, a transformer L23 for converting unbalanced power, a DC blocking capacitor C8, and a resistor R8 which constitutes the attenuation circuit 211.
A circuit for distributing a signal is connected through R10.

The circuit for distributing this signal operates in the same manner as in FIG. That is, when the UHF band circuit operates, the power supply voltage + UB is supplied to the terminal T5, and a signal is supplied to the input switching circuit 19 via the signal switching diode D1 and the DC blocking capacitor C10. On the other hand, when the VHF band circuit operates, the power supply voltage + VB is supplied via the terminal T4, and a signal is supplied to the input switching circuit 20 via the signal switching diode D2 and the DC blocking capacitor C9.

In the operation of the circuit shown in FIG. 8, a signal supplied from the input terminal 1 and the HPF 2 to the broadband amplifier 21E is amplified by the amplifier 1E which is a balanced amplifier. At this time, the amplification elements Q1 and Q2 of the amplification circuit 1E
Perform complementary amplification and balanced amplification operation. In other words, since each of the amplifying elements Q1 and Q2 operates in the opposite phase every half cycle, the output level after the combination becomes higher than the output level before the combination by 3 dB.

The output signal from the amplifier circuit 1E passes through the balanced / unbalanced conversion transformer L23, the DC blocking capacitor C8, and the attenuating circuit 211, and via the circuit for distributing the signal, the input switching circuits 19 and 20. Or one of them.

The circuit of FIG. 8 is superior in isolation to that of FIG. 5, and can obtain 15 to 20 dB in FIG. 5, while obtaining 20 to 25 dB in FIG.

The wide-band amplifier circuit 21C shown in FIGS.
, 21E and the broadband amplifier circuit 2 of FIGS. 3, 4 and 7
When comparing 1A, 21B and 21D, the latter has a gain of almost 0 dB, while the former has a gain of several dB. In addition, the input return loss and local return can be improved at substantially the same level in both cases. In particular,
In the circuit of FIG. 8, two float balloons for phase conversion of the balance-unbalance conversion transformers L31 and L23 are provided at the input / output stages of the broadband amplifier circuit 21E, respectively. Obtainable.

In the circuit of FIG. 8, capacitors C1 to C10
Is 1000 to 10000 pF, and resistors R3 and R5 are 330
Ω, resistors R4 and R6 are 270 kΩ, resistors R2 and R7 are 1
20 kΩ, R1 is 47Ω, R8 and R9 are 220Ω, R1
0 has a value of 24Ω, and R11 and R12 have a value of 1 kΩ.

[Third Embodiment] FIG. 9 is a block diagram of a cable modem tuner according to a third embodiment of the present invention. The configuration of the tuner for the cable modem of FIG. 9 differs from that of FIG.
The point is that the LPF 23 is additionally provided between F2 and F2 to improve the isolation. FIG. 1 shows another configuration of FIG.
Therefore, the description is omitted.

The cutoff frequency fc of the LPF 23 is determined by the local oscillation frequency of the local oscillation circuit 10 (14). FIG. 10 is a graph showing the relationship between the frequency of the input signal and the amount of attenuation in the LPF 23 of FIG. FIG.
At 0, the horizontal axis represents the frequency f (MHz) of the input signal, and the vertical axis represents the attenuation (dB). As shown in the figure, the cutoff frequency fc is set in the vicinity of where the attenuation determined by the local oscillation frequency fl becomes -3 dB.

The circuit configurations of the broadband amplifier circuit 21 and the LPF 23 shown in FIG. 9 are shown in the following first and second embodiments.

(Embodiment 1) FIG. 11 shows a broadband amplifier circuit and an LPF according to Embodiment 1 of Embodiment 3 of the present invention.
FIG. 3 is a block diagram of the configuration of FIG.

In FIG. 11, an LPF 231 and a broadband amplifier 21F are connected in series between the HPF 2 and the input switching circuits 19 and 20.

The LPF 231 includes inductors L41 to L4
6. Capacitors C41 and C48 to C51, DC blocking capacitor C47, bias resistor R47, terminal T1 to which tuning voltage + VT corresponding to a desired reception channel is applied
0, and a variable capacitance diode D41.

In the LPF 231, the variable capacitance diode D4
1 is applied and the local oscillation circuit 10 (1
The frequency (cutoff frequency f _c ) at which the signal attenuation becomes −3 dB is variably set in accordance with the input of the same tuning voltage + VT applied to 4).

The broadband amplifier circuit 21F connects the amplifier circuit 1F and the attenuation circuit 211 composed of the resistors R5 to R7 in series. The amplifier circuit 1F has the same configuration as the amplifier circuit 1A shown in FIG.

The gain of 5-6 dB is obtained in the amplifier circuit 1F, and the gain of -4 dB is obtained in the attenuation circuit 211.
Is designed to obtain a gain of

[0107] In operation, applied to wide-band amplifier circuit 21F band signals according to cut-off frequency f _c of the signal is set at the given LPF231 to LPF231 through the input terminal 1 and HPF2 passes through.

As described above, the tuning voltage +
Since only the bands of the signals according to cut-off frequency f _c is set by VT passes, signals other than the adjustment band corresponding to the reception channel is effectively damped, to operate so as not given to the next stage circuit .

In the broadband amplifier circuit 21F, the input signal is amplified in the amplifier circuit 1F in the same manner as in FIG. 3 and then attenuated in the attenuator 211 and output to the input switching circuits 19 and 20.

(Embodiment 2) FIG. 12 shows a broadband amplifier circuit and an LPF according to Embodiment 2 in Embodiment 3 of the present invention.
It is a block diagram of. 9 and LP.
F23 is the broadband amplifier circuit 21F and the LPF 232 shown in FIG.
May be configured as follows.

The difference between the circuit configuration of FIG. 11 and that of FIG. 12 is that the LPF 231 of FIG.
F232 has been substituted. The other configuration in FIG. 12 is the same as that in FIG. 11, and the description is omitted.

The LPF 232 in FIG. 12 and the LPF 2 in FIG.
31 is different from LPF23 in that LPF232 is
1 and the capacitor C instead of the variable capacitance diode D41
52 in that a parallel circuit of SW 52 and SW (short for switching) diode D42 is provided. The other configuration of the LPF 232 is the same as that of the LPF 231 and will not be described.

In the LPF 232, the ON / OFF control of the SW diode D42 is performed depending on whether or not the power supply voltage + VB is applied when the circuit for receiving the VHF signal from the terminal T7 (the circuit after the input switching circuit 20) operates. C4
7 and C52 are used to switch the capacitance component.
32 of the cut-off frequency f _c is changed. Thus the cut-off frequency f _c according to the desired receiving frequency band in LPF232 is switched. Thus LP
F23 reduces (attenuates) local leakage.

FIG. 13 is a diagram showing a circuit configuration in which the LPFs of FIGS. 11 and 12 are used together. May be used in combination switching換手method cut-off frequency f _c of the LPF231 and 232 as shown in FIG. 13. In this case, the desired reception band (one of the UHF band and the VHF band)
Cut-off frequency f _c on the basis of both the desired received channel by being switched, is further locally re cage effectively reduced (attenuated) and.

In the circuits shown in FIGS. 11 and 12, the amplification circuit 1F has a gain of 5 to 6 dB, and the attenuation circuit 211
At a gain of -4 dB and finally 1-2 dB
Is designed to have a gain of Specifically, in FIG. 11, the capacitors C41, C2 to C6 and C47 are 1
000 to 10000 pF, capacitors C50 and C5
1 is 5 pF, capacitors C48 and C49 are 1 pF,
The coil L6 is 1 μH, the resistor R1 is 47Ω, and the resistor R2 is 1
80kΩ, resistor R3 is 330Ω, resistor R4 is 270k
Ω, resistors R5 and R6 have a value of 220Ω, resistor R7 has a value of 24Ω, and resistor R47 has a value of 47 kΩ. In the circuit of FIG. 12, the capacitor C52 has a value of 10 pF and the resistor R48 has a value of 2.2 kΩ. The values of the other elements in FIG. 12 are the same as those in FIG.

[Fourth Embodiment] FIG. 14 is a block diagram of a tuner for a cable modem according to a fourth embodiment of the present invention. The configuration of the cable modem tuner of FIG. 14 differs from that of FIG.
1 and an input / output switching circuit 19 and 20 in which a variable trap circuit 24 for reducing local leakage is additionally provided. The other configuration of FIG. 14 is the same as that of FIG. Here,
Although the variable trap circuit 24 is provided at the output stage of the broadband amplifier circuit 21, the same effect can be obtained by providing it at the input stage.

The circuit configuration of the wideband amplifier circuit 21 and the variable trap circuit 24 shown in FIG. 14 is shown in the first embodiment.

(Embodiment 1) FIG. 15 is a block diagram of a wide band amplifier circuit and a variable trap circuit according to Embodiment 1 of the present invention in a fourth embodiment. In FIG. 15, HP
Between the F2 and the input switching circuits 19 and 20, a wideband amplifier circuit 21G, a variable trap circuit 241 and a resistor R5
To R7 are connected.

In the circuit shown in FIG. 15, a broadband amplifier circuit 2 includes an amplifier circuit 1G configured similarly to the amplifier circuit 1A shown in FIG.
An attenuation circuit 211 is connected to the 1G output stage via DC blocking capacitors C3 and C13. Further, a variable trap circuit 241 for a local leakage signal on the connection line is connected in the middle of the connection line between the broadband amplification circuit 21G and the attenuation circuit 211.

The variable trap circuit 241 includes a DC blocking capacitor C14, a variable capacitance diode D9 for resonance, a resonance inductor (trap coil) L58, a bias resistor R58, and a terminal T9. A resonance circuit is configured by the resonance variable capacitance diode D9 and the resonance inductor L58 connected in parallel with the variable diode D9.

A tuning voltage + VT variably set in accordance with a desired reception channel is applied from a terminal T9 to a resonance variable capacitance diode D9 via a bias resistor R8. Thus, the resonance circuit including the resonance variable capacitance diode D9 and the resonance inductor L58 oscillates at the local oscillation frequency of the local oscillation circuit 10 or 14 at the subsequent stage or higher. Therefore, the output signal from the wideband amplifier circuit 21G in the preceding stage is attenuated (attenuated) by the variable trap circuit 241 after the signal component other than the frequency corresponding to the desired reception channel or higher is absorbed by the variable trap circuit 241, and then the attenuation in the next stage. The circuit 211 is provided.

In the circuit of FIG. 15, the capacitor C13
And C14 are 1000 pF, and resistor R58 is 47 kΩ.
Has the value of Other values of the element are the same as those of FIG.

Each of the circuits shown in FIGS. 11, 12, 13 and 15 is a circuit for reducing local leakage, but a tuner for a cable modem whose characteristics are further improved by using each circuit in combination. Can be obtained.

The embodiments disclosed this time are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

[Brief description of the drawings]

FIG. 1 is a block diagram of a tuner for a cable modem according to a first embodiment of the present invention.

FIG. 2 is a graph showing a relationship between a reception frequency and an input return loss at an input terminal of FIG. 1;

FIG. 3 is a block diagram of a broadband amplifier circuit according to Example 1 in Embodiment 1 of the present invention;

FIG. 4 is a block diagram of a broadband amplifier circuit according to Example 2 in Embodiment 1 of the present invention.

FIG. 5 is a block diagram of a broadband amplifier circuit according to Example 3 in Embodiment 1 of the present invention.

FIG. 6 is a block diagram of a cable modem tuner according to a second embodiment of the present invention.

FIG. 7 is a block diagram of a wideband amplifier circuit and a signal distribution circuit according to a first embodiment in the second embodiment of the present invention.

FIG. 8 is a block diagram of a wideband amplifier and a signal distribution circuit according to a second embodiment of the present invention.

FIG. 9 is a block diagram of a tuner for a cable modem according to Embodiment 3 of the present invention.

FIG. 10 is a graph showing the relationship between the frequency of an input signal and the amount of attenuation in the LPF of FIG. 9;

FIG. 11 is a block diagram of a broadband amplifier and an LPF according to Example 1 in Embodiment 3 of the present invention.

FIG. 12 is a block diagram of a broadband amplifier and an LPF according to a second embodiment in the third embodiment of the present invention.

FIG. 13 is a diagram showing a circuit configuration in which the LPFs of FIGS. 11 and 12 are used together.

FIG. 14 is a block diagram of a tuner for a cable modem according to a fourth embodiment of the present invention.

FIG. 15 is a block diagram of a wideband amplifier circuit and a variable trap circuit according to Example 1 in Embodiment 4 of the present invention.

FIG. 16 is a block diagram of a conventional cable modem tuner.

FIG. 17 is a graph showing a relationship between a reception frequency and an input return loss at the input terminal of FIG. 16;

[Explanation of symbols]

 2 HPF 3-5 RF amplification input tuning circuit 6 and 8 RF amplifier 16-18 RF amplification output tuning circuit 9 and 13 Mixing circuit 10 and 14 Local oscillation circuit 21, 21A-21G Broadband amplification circuit 22, 22A and 22B Signal distribution circuit 23, 231 and 232 LPFs 24, 241 Variable trap circuit 211 attenuating circuit Note that the same reference numerals in the drawings denote the same or corresponding parts.

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference)

Claims (11)

[Claims] 1. An input unit for receiving and inputting a CATV signal, extracting and outputting a high-frequency signal, and a signal provided for each of at least two or more reception bands of the CATV signal and provided from the input unit side Amplifying and tuning sections that perform tuning processing while inputting and amplifying the signals, and are provided in correspondence with each of the amplifying and tuning sections, and desirably follow a predetermined signal given by inputting and outputting a signal output from the amplifying and tuning section. A tuner for a cable modem comprising at least a frequency conversion unit for converting and outputting an intermediate frequency signal corresponding to a channel, wherein the tuner is provided between the input unit and the amplification tuning unit, and the input unit A buffer for inputting and processing the high-frequency signal output from the amplifier and outputting the processed signal to the amplification tuning unit, wherein the buffer unit couples the input unit and the amplification tuning unit. Characterized in that it is provided to the tuner for a cable modem. 2. The cable according to claim 1, wherein the buffer unit includes a broadband amplifying unit that receives the high-frequency signal output from the input unit, amplifies the signal over a wide band, and outputs the amplified signal. Tuner for modem. 3. The wide-band amplifying unit includes a wide-band amplifying circuit connected to one or more stages.
The tuner for a cable modem according to the item. 4. The tuner for a cable modem according to claim 2, wherein the broadband amplifier includes a balanced amplifier composed of two broadband amplifiers connected in a complementary symmetric manner. 5. The tuner for a cable modem according to claim 4, wherein the broadband amplifier includes a balun circuit at each of an input stage and an output stage of the balanced amplifier. 6. The signal processing apparatus according to claim 1, wherein the buffer unit further includes a signal distribution unit provided at an output stage of the wideband amplification unit and receiving an output signal of the wideband amplification unit and distributing the input signal to each of the amplification tuning units. Item 6. A tuner for a cable modem according to any one of Items 2 to 5. 7. The filter section, which is provided at an input stage of the broadband amplification section, receives the high-frequency signal from the input section, extracts a signal of a desired band, and outputs the signal to the wideband amplification section. The tuner for a cable modem according to any one of claims 2 to 5, further comprising: 8. The cable modem tuner according to claim 7, wherein the filter section is a low-pass filter whose cutoff frequency is variably set in accordance with the given predetermined signal. 9. The filter according to claim 7, wherein the filter unit is a low-pass filter whose cutoff frequency is variably set in accordance with a desired reception band among the at least two or more reception bands. The tuner for the cable modem described. 10. The case where the buffer further includes an attenuator provided at one of an input stage and an output stage of the broadband amplifier, wherein the attenuator is provided at an input stage of the broadband amplifier. To input the high-frequency signal output from the input unit, attenuate signals other than the frequency band to be adjusted by the amplification tuning unit and the frequency conversion unit, and output the signal to the wideband amplification unit; When provided at the output stage of the broadband amplifier, a signal output from the broadband amplifier is input, and the signals other than the frequency band to be adjusted by the amplification tuning unit and the frequency converter are attenuated. The tuner for a cable modem according to any one of claims 2 to 5, wherein the signal is output to the amplification tuning unit. 11. The frequency conversion section mixes a local oscillation circuit oscillating at a frequency according to the predetermined signal, a signal output from the amplification tuning section, and an oscillation signal of the local oscillation circuit to convert the intermediate frequency signal. The tuner for a cable modem according to claim 10, further comprising: a mixing circuit that outputs a signal; and wherein the attenuation unit is a trap circuit that tunes to an oscillation frequency of the local oscillation circuit.