JP2000040976A - Tuner for cable modem - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tuner for cable modem with which production cost can be reduced and miniaturization can be attained. SOLUTION: An inductor element constituting a tuner circuit in a reception circuit for the UHF band of a tuner A for cable modem is composed of striplines 21A, 37A and 38A. Thus, the working of a tuning coil related to control at the time of tuner production is omitted, and miniaturizing and flattening can be attained by the striplines.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tuner for a cable modem, and more particularly to a tuner for a cable modem which can be easily adjusted and is downsized.

[0002]

2. Description of the Related Art In CATV, HFCs (Hybrid Fiber / Coax) employing 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 mod
(short for ulation) can provide a high-speed data line having a bandwidth of 6 MHz and a transmission speed of 30 Mbit / sec.

[0004] By using a cable modem for the above 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-described cable modem has a tuner, and the tuner for the cable modem is 470 to 860.
UFH band having MHz (B3 band), 170-
VHF High band (B2 band) with 470 MHz and VHF Lo with 54-170 MHz
A receiving circuit is provided for each of the w bands (B1 bands). However, band division is not specified here.

FIG. 4 is a circuit diagram of a tuner for a cable modem for explaining the background of the present invention. In the circuit of the tuner B for the cable modem shown in FIG. 4, the high-frequency amplification input tuning circuit is improved to improve the B3 band characteristics.

In FIG. 4, a tuner for a cable modem has an input terminal 1, an HPF (abbreviation of high-pass filter) 2, a data terminal 41, and a B1 to B3 band for communication connection between a line (not shown) and the tuner. Receiving circuits, IF (intermediate frequency) amplifier circuits 55 and 57, SAW filter 56, and IF output terminal 15
including. HPF2 may be an IF filter.

The data signal input from the data terminal 41 is connected to the input terminal 1 through the upstream circuit 40.

The above-mentioned receiving circuits for the B1 to B3 bands include input signal switching circuits 18 to 20 to which a switching method using a switching diode or a method using a filter based on band division is applied, and a high-frequency amplification input tuning circuit. 3 to 5 and the high-frequency amplifier 6
To 8 and a high frequency amplification output tuning circuit 70 to 72
, Each of the mixing circuits 9 to 11, and each of the local oscillation circuits 12 to 14.

The input signal switching circuits 18 to 20 include B1 to B3
A received signal of a band is input, and only a received signal of a predetermined frequency band is selectively output.

The high frequency amplification input tuning circuits 3 to 5 tune each of the reception signals selected and output by the input signal switching circuits 18 to 20 to a desired frequency (frequency of a desired channel) using a tuning coil or the like in each band. And output.

Each of the high-frequency amplifiers 6 to 8 amplifies and outputs the output signals of the high-frequency amplification input tuning circuits 3 to 5 so as to prevent deterioration of the SN ratio in each band.

Each of the high frequency amplification output tuning circuits 70 to 72 tunes the output signal of each of the high frequency amplifiers 6 to 8 to a desired frequency in each band by using a tuning coil or the like and outputs the tuned signal.

The local oscillation circuits 12 to 14 oscillate stably so as to generate a predetermined intermediate frequency corresponding to each band, and the mixing circuits 9 to 11 localize the signals output from the high frequency amplification output tuning circuits 70 to 72. Since it is converted into an intermediate frequency signal by the oscillation signal, the local oscillation circuits 12 to 14 and the mixing circuits 9 to 11
Thus, a frequency conversion circuit for each band is formed.

As for the B3 band receiving circuit, a high frequency amplification output tuning circuit 70 is provided at the output stage of the high frequency amplifier 6.

Thereafter, the output signal of each receiving circuit is amplified to a predetermined level by an IF amplifier circuit 55, and then the SAW filter 56
The frequency is converted to a predetermined level by the IF amplifier circuit 57 and output via the IF output terminal 15.

In the receiving circuit for the B3 band, the portion related to the high-frequency amplification input tuning circuit 3, the high-frequency amplification output tuning circuit 70 and the local oscillation circuit 12 is configured to improve the B3 band characteristics.

The high frequency amplification input tuning circuit 3 includes coupling capacitors 16 and 24 for cutting a DC component, an impedance matching coil 17, a tuning coil 21, a capacitance change ratio suppressing capacitor 22, a variable capacitance diode 23, and a bias resistor 2.
5, including an RFC (high frequency choke coil) 26, a bypass capacitor 27, a tuning voltage terminal 28, and a UHF band power supply voltage terminal 29.

By the coupling capacitors 16 and 24 and the impedance matching coil 17, impedance matching between the input signal switching circuit 18 in the preceding stage and the high frequency amplifier 6 and the high frequency amplification input tuning circuit 3 in the next stage is achieved.

A tuning circuit is formed by the tuning coil 21, the capacitance change ratio suppressing capacitor 22 and the variable capacitance diode 23. The tuning point of this tuning circuit is adjusted by the tuning voltage supplied from the tuning voltage terminal 28 to the variable capacitance diode 23 via the bias resistor 25.

A predetermined bias voltage in the B3 band is supplied to the high frequency amplifier 6 in the next stage from the power supply voltage terminal 29 in the UHF band via the RFC 26.

In the high-frequency amplification input tuning circuit 3, a bias to the high-frequency amplifier 6 at the subsequent stage is supplied via the RFC 26, so that a resonance circuit is formed by the RFC 26 and the input capacitance of the high-frequency amplifier 6 at the subsequent stage.

The high frequency amplification output tuning circuit 70 includes a bypass capacitor 30, an RFC 31, a damping resistor 32, coupling capacitors 33 and 39, variable capacitance diodes 34 and 48, bias resistors 35 and 42, capacitance change ratio suppressing capacitors 36 and 51, and a tuning coil. 37 and 38 are included.

Here, a primary-side tuning circuit is formed by the variable capacitance diode 34 and the tuning coil 37, and a secondary-side tuning circuit is formed by the variable capacitance diode 48 and the tuning coil 38. Tuning coils 37 and 38 are coupled.

The tuning coils 21, 37 and 38 are so-called air-core coils without an iron core.

In connection with the adjustment of the oscillation frequency of the local oscillation circuit 12, the bias resistor 43 and the coupling capacitor 4
4, a variable capacitance diode 45, a capacitance change ratio suppressing capacitor 46, and a resonance coil 47

In operation, the CATV signal is between 5 and 42M.
It has an upstream signal of Hz and a downstream signal of 54 to 860 MHz, and is input / output between the tuner circuit and a cable (not shown) via the input terminal 1.

A data signal subjected to quadrature phase shift modulation from a QPSK (quadrature phase shift keying) transmitter (not shown) is introduced into the upstream signal via a data terminal 41. The data signal is supplied to the input terminal 1 via the data terminal 41 and the upstream circuit 40.

The downstream signal passes through an HPF (IF filter) 2 and is supplied to input switching circuits 18 to 20.
Of the two receiving circuits, only the receiving circuit whose downlink signal frequency corresponds to the operating frequency of the circuit operates, and the other receiving circuits do not operate. The operation of each receiving circuit is common.

Next, the operation state of the receiving circuit of each band will be described. The CATV signal is supplied to the input switching circuits 18-2.
0 and high-frequency amplifier output tuning circuit 7 which is amplified by high-frequency amplifiers 6-8 via high-frequency amplifier input tuning circuits 3-5.
It is derived as a received signal via 0-72.

After that, the received signal is converted into an intermediate frequency signal by the mixing circuits 9 to 11 and the local oscillation circuits 12 to 14, and is LOW IF converted by the IF amplifier circuits 55 and 57 and the SAW filter 56, and is output to the output terminal 15. Derived.

In the series of operations, channel selection data is transmitted from a CPU (not shown) to a PLL channel selection circuit (not shown), and channel selection is performed based on the data. This is realized by operating the switching circuit and switching the power supply of each band.

[0032]

When manufacturing the circuit of the tuner B for the cable modem shown in FIG.
7 and 38 and the resonance coil 47 had to be adjusted.

More specifically, the air-core coils 21, 37 and 3
By changing the inductance by changing the winding space of the coil of No. 8 and changing the resonance point of the tuning circuit, the resonance coil 47 is adjusted to adjust the signal waveform in the high-frequency amplifier circuit. As a result, variations in capacitance of elements such as transistors, capacitors, and variable capacitance diodes and variations in inductance of the coil itself have been absorbed.

In this case, the time required for processing the coil for adjustment accounts for 30% of the entire adjustment time of the tuner B for the cable modem, and the adjustment by the tuner cannot be performed efficiently.

In the cable modem tuner B shown in FIG. 4, the resistors and capacitors are formed into chips and can be miniaturized, whereas the tuning coils 21, 37 and 38, which are air-core coils, are not provided. The shape is physically determined by the inductor, and miniaturization is difficult.

Tuning coils 21 and 37 of the air-core coil
And 38 have been tried to be automatically inserted or surface-mounted on the substrate of the tuner circuit. However, the efficiency of manufacturing cost reduction is low, and no adjustment is required by omitting the coil.

Therefore, an object of the present invention is to provide a tuner for a cable modem in which the manufacturing cost can be reduced and the size can be reduced.

[0038]

According to a first aspect of the present invention, there is provided a tuner for a cable modem, comprising:
An input unit for selecting and outputting to any one of a plurality of different frequency bands including F, a first inductance element, and receiving signals selectively output from the input unit in each system by a first inductance element And an amplifying unit for amplifying the output signal of each input tuning unit in each system, and a second inductance element, and outputting the output signal of each amplifying unit to each system. At least includes an output tuning unit that tunes to the desired frequency by the second inductance element and outputs the signal, and a frequency conversion unit that converts an output signal of each output tuning unit to a signal of a desired intermediate frequency in each system. , UHF, the first and second inductance elements are constituted by strip lines.

Therefore, in the UHF system, since the inductance element for tuning in the input and output tuning sections is a strip line, adjustment of the tuning coil is omitted, and the adjustment cost at the time of manufacturing is reduced.

Further, since the inductance element is formed of a strip line as described above, the flattening and miniaturization of the cable modem tuner are promoted.

Further, since the inductance element is a strip line as described above, the adjustment of the inductance element is omitted and the processing time for the inductance element is omitted, so that the manufacturing cost for the cable modem tuner is reduced.

According to a second aspect of the present invention, in the tuner for a cable modem according to the first aspect, the output tuning section in the UHF system includes a primary side tuning section and a secondary side tuning section each having a strip line. Including
The strip lines of the primary-side and secondary-side tuning units are coupled, and the coupling unit is provided with an inductance unit.

Therefore, the variation of the pass band width in the UHF system by the mass production lot at the time of manufacturing the cable modem tuner is absorbed by the inductance portion, and the adjustment cost at the time of manufacturing the tuner is reduced.

According to a third aspect of the present invention, there is provided a cable modem tuner according to the first or second aspect, wherein a local oscillation circuit in which a frequency converter in a UHF system oscillates at a predetermined frequency, and a local oscillation circuit. And a mixing circuit for inputting the oscillation signal of the output tuning section and the output signal of the output tuning section, converting the output signal into the above-mentioned intermediate frequency signal, and outputting the intermediate frequency signal. It is adjusted optimally in advance.

Therefore, the oscillation frequency of the local oscillation circuit is optimally adjusted according to the characteristics of the output signal of the output tuning circuit, that is, the dispersion of the tuning characteristics, and the deviation of tracking is absorbed. As a result, the processing time during the production of the cable modem tuner is reduced, and the production cost is reduced.

According to a fourth aspect of the present invention, there is provided a tuner for a cable modem in a UHF system at the time of adjustment, an alternative oscillation circuit for oscillating a signal superimposed on an output signal of an output tuning circuit instead of a local oscillation circuit, and an output tuning circuit. A monitor circuit for monitoring and outputting a superimposed signal in which the oscillation signal of the alternative oscillation circuit is superimposed on the output signal of the circuit. Then, the oscillation signal of the alternative oscillation circuit is adjusted to match the waveform of the output signal of the output tuning circuit based on the superimposed signal output from the monitor,
The oscillation frequency of the local oscillation circuit is adjusted using the adjustment amount.

Therefore, the oscillation frequency of the local oscillation circuit can be optimally adjusted in accordance with the variation in the tuning characteristics caused by the variation in the capacitance of the capacitance element of the output tuning circuit during the manufacture of the cable modem tuner. And the manufacturing cost is reduced.

[0048]

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

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

B3 of tuner B for cable modem in FIG.
The high-frequency amplifier circuit of the band is formed to include a tuning circuit using an air-core coil, and it is necessary to adjust the input tuning coil 21, the output tuning coils 37 and 38, and the resonance coil 47 related to the local oscillation circuit 12 at the time of manufacturing the tuner. However, in the cable modem tuner A of FIG. 1, the size of the B3 band high-frequency amplification tuning circuit is reduced and the adjustment method is improved. Where B3
The improvement of the band high-frequency amplification tuning circuit will be specifically described below.

The difference between the circuit of the cable modem tuner A of FIG. 1 and that of FIG. 4 is that the high-frequency amplification input and output tuning circuits 3 and 70 of FIG.
High-frequency amplification input and output tuning circuits 3A and 70A
In that it has been replaced by The other configuration in FIG. 1 is the same as that in FIG. 4, and the description is omitted here.

The high-frequency amplification input and output tuning circuits 3A and 70A of FIG. 1 are compared with the high-frequency amplification input and output tuning circuits 3 and 70 of FIG.
The tuning coils 21, 37 and 38 of FIG. 4 are replaced with the strip lines 21A, 37A and 38A of FIG. 1, and a coupling coil 52 is added to FIG.
The high frequency amplification input and output tuning circuits 3A and 7 of FIG.
The other configuration of 0A is the same as that of FIG. 4, and the description is omitted here.

In the high frequency amplification input and output tuning circuits 3A and 70A of FIG. 1, the tuning coils 21, 37 and 3 of FIG.
8 is omitted by forming strip lines 21A, 37A and 38A on a printed circuit board together with other circuit groups of the tuner.

By forming a tuning circuit including these strip lines, only the resonance coil 47 related to the local oscillation circuit 12 needs to be adjusted when the tuner is manufactured. Note that the strip line is mainly B3 (UH
F) Formation is possible in a band, and difficult in other bands.

In FIG. 1, the tuning coils in the B3 band tuning circuit are strip lines 21A, 3A as described above.
By changing to 7A and 38A print coils (pattern coils formed on a printed circuit board),
Variations in the inductor of the coil itself are minimized. Then, the oscillation frequency of the local oscillation circuit 12 is adjusted so as to match the variation in the tuning characteristics due to the variation in the capacitance element such as the diode, the capacitor, and the transistor. That is, a method is adopted in which the oscillation signal of the local oscillation circuit 12 is added to the band-pass characteristic, which is a high-frequency amplification characteristic, to perform adjustment.

FIG. 2 is a diagram showing an equipment system for adjusting the oscillation frequency of local oscillation circuit 12 in FIG.

In the figure, this equipment system is Sweep SG
1 includes a cable modem tuner A, an IF marker SG81, a detector 82, and an oscilloscope 83 shown in FIG.

The output signal of the IF marker SG81 is applied to indicate the position (frequency) of the local oscillation signal on the IF signal instead of the local oscillation signal from the local oscillation circuit 12.

The Sweep SG 80 stably oscillates a reference sweep waveform (waveform showing high-frequency amplification characteristics) and supplies the signal to the terminal 1 of the cable modem tuner A.

In this case, the local oscillation circuit 12 of the cable modem tuner A is in a stopped state.

The sweep waveform given to the cable modem tuner A is output as a test point signal TP of the IF signal at the output stage of the IF amplifier circuit 55 in FIG. 1, and the output signal of the IF marker SG81 is superimposed. The resulting superimposed signal is output by the oscilloscope 83 via the detector 82.

At this time, the output of the IF marker SG81 is adjusted while referring to the output of the oscilloscope 83, so that the waveform output by the oscilloscope 83 does not vary and only the waveform of the IF signal is obtained. IF marker SG at this time
Since the oscillation frequency of the local oscillation circuit 12 is uniquely determined based on the output adjustment amount of 81, the diode of the tuning circuit,
Variations in tuning characteristics due to variations in capacitance of capacitors, transistors and the like can be absorbed by adjusting the oscillation frequency of the local oscillation circuit 12.

In the tuner for the cable modem shown in FIG.
A coupling coil 52 is provided to suppress variations in the pass band width, which is a combined waveform of the three high-frequency amplified waveforms.

FIG. 3 is a detailed circuit diagram of the coupling coil 52 of FIG. 1 and its vicinity. In the drawing, the coupling coil 52 is configured by connecting the printed inductors 60 in parallel or connecting the printed inductor 60 and the chip inductor 61 in parallel to the coupling portion of the strip lines 37A and 38A. Note that a printed inductor is an inductor formed by a printed coil. A chip inductor is a printed coil formed on a chip.

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 circuit diagram of a tuner for a cable modem according to an embodiment of the present invention.

FIG. 2 is a diagram showing an equipment system for adjusting an oscillation frequency of a local oscillation circuit 12 in FIG.

FIG. 3 is a detailed circuit diagram of the coupling coil 52 of FIG.

FIG. 4 is a circuit diagram of a tuner for a cable modem for explaining the background of the present invention.

[Explanation of symbols]

 18-20 Input signal switching circuit 3-5 and 3A High frequency amplification input tuning circuit 6-8 High frequency amplifier 70-72 and 70A High frequency amplification output tuning circuit 9-11 Mixing circuit 12-14 Local oscillation circuit 21A, 37A and 38A Stripline In the drawings, the same reference numerals indicate the same or corresponding parts.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5C025 AA25 5J103 AA05 AA09 BA07 CA04 CA05 CA08 CB05 CB07 DA01 DA03 DA04 DA06 DA16 EA00 EA01 EA03 EA12 5K062 AA10 AA11 AB10 AB12 AC02 AD04 AE01 BA03 BB10 BC03 BC03 BC10

Claims (4)

[Claims] 1. An input unit for receiving a multi-wave received signal and selecting and outputting the signal to one of a plurality of different frequency bands including UHF, and a first inductance element, wherein the input unit is selected by the input unit. An input tuning unit that tunes each of the output received signals to a desired frequency in the respective systems by the first inductance element and outputs the tuned signals; an amplifying unit that amplifies the output signals of the input tuning units in the respective systems; An output tuning unit that has two inductance elements and tunes the output signal of each of the amplifying units to the desired frequency by the second inductance element in each system, and outputs the output signal of each of the output tuning units; At least a frequency conversion unit for converting the signal into a signal of a desired intermediate frequency. Inductance element is characterized in that it consists of strip line, cable modem tuner. 2. The output tuning section in the UHF system includes a primary side tuning section and a secondary side tuning section each having the strip line, and the strip lines of the primary side and secondary side tuning sections are coupled. The tuner for a cable modem according to claim 1, wherein the coupling part is provided with an inductance part. 3. The frequency conversion unit in the UHF system receives a local oscillation circuit that oscillates at a predetermined frequency, an oscillation signal of the local oscillation circuit and an output signal of the output tuning unit, and converts the oscillation signal into an intermediate frequency signal. And a mixing circuit for converting and outputting the predetermined frequency. The predetermined frequency of the local oscillation circuit is optimally adjusted in advance according to characteristics of an output signal of the output tuning unit. The tuner for the cable modem described. 4. An alternative oscillation circuit for oscillating a signal superimposed on an output signal of the output tuning circuit instead of the local oscillation circuit in the UHF system when adjusting the tuner for the cable modem; A monitor circuit for monitoring and outputting a superimposed signal in which the oscillation signal of the alternative oscillation circuit is superimposed on the output signal of the tuning circuit, wherein the oscillation signal of the alternative oscillation circuit is output based on the superimposed signal that is monitored and output. 4. The tuner for a cable modem according to claim 3, wherein an adjustment is made so as to match a waveform of an output signal of the tuning circuit, and an oscillation frequency of the local oscillation circuit is adjusted using the adjustment amount.