Cable modem tuner

• US 20010016950A1
• Filed: 02/14/2001
• Published: 08/23/2001
• Est. Priority Date: 02/14/2000
• Status: Active Grant

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Matsuura, Syuuji
• Granted Patent: US 7,363,648 B2
• Time in Patent Office: Days
• US Class Current: 725/111
• CPC Class Codes: H03J 5/244 using electronic means

Abstract

An IF input signal corresponding to a selected reception channel is applied through an SAW filter to an IF-AGC circuit, the amplitude of the signal is adjusted to a prescribed level, and the signal is thereafter supplied to a down converter unit. The down converter unit selectively outputs a Low-IF signal provided by down-converting the IF input signal and the High-IF signal amplified without frequency conversion, in accordance with an external instruction. A filter circuit has its cut off frequency selectively set to pass the Low-IF signal only, or both the Low-IF and High-IF signals.

Claims

1. A cable modem tuner, comprising:

a tuner circuit taking and amplifying a signal corresponding to a reception channel from input signals, and converting to an intermediate frequency signal of a first frequency band; and

a down converter circuit receiving the intermediate frequency signal of said first frequency band from said tuner circuit, and selectively outputting an intermediate frequency signal of said first frequency band or a second frequency band lower than said first frequency band;

wherein

said down converter circuit includes

a local oscillation circuit generating an oscillation signal corresponding to said second frequency band in a first mode in which the intermediate frequency signal of said second frequency band is output, and stopping generation of said oscillation signal in a second mode in which the intermediate frequency signal of said first frequency band is output,

a mixer circuit for mixing the intermediate frequency signals of said first frequency band input to said down converter circuit with an output of said local oscillation circuit, and

a filter circuit receiving an output signal from said mixer circuit and passing a signal of a frequency corresponding to a set cut off frequency.

2. The cable modem tuner according to

claim 1

, wherein

said tuner circuit includes a first automatic gain control circuit for adjusting amplitude of a signal corresponding to said reception channel to a prescribed level,

said tuner further comprising

a second automatic gain control circuit provided between said tuner circuit and said down converter circuit, for adjusting amplitude of the intermediate frequency signal of said first frequency band to a prescribed level.

3. The cable modem tuner according to

claim 2

, wherein total gain attained by said first and second automatic gain control circuits is at least 55 dB.

4. The cable modem tuner according to

claim 1

, wherein

said tuner circuit and said down converter circuit output signals of non-parallel type, said cable modem tuner further comprising

a signal converting circuit receiving an output of said down converter and converting to a parallel type signal.

5. The cable modem tuner according to

claim 1

, wherein

said mixer circuit amplifies the intermediate frequency signal of said first frequency band in said second mode.

6. The cable modem tuner according to

claim 1

, wherein

said local oscillation circuit includes

an oscillation element oscillating at said second frequency band,

a first bipolar transistor receiving at an input electrode an output of said oscillation element,

a first bias resistance coupled between the input electrode of said first transistor and a first voltage node;

and

a second bias resistance connected between an output electrode of said first bipolar transistor and a ground node; and

said mixer circuit includes

a second bipolar transistor connected to said first voltage node, and receiving at an input electrode an output of said oscillation element and the intermediate frequency signal of said first frequency band, and

a third bias resistance connected between the input electrode of said second bipolar transistor and a second voltage node supplying a voltage higher than said first voltage node.

7. The cable modem tuner according to

claim 6

, wherein

said local oscillation circuit includes a switch element of which on/off is instructed externally, connected parallel to said oscillation element,

said switch element turning on/off in said first and second modes, respectively.

8. The cable modem tuner according to

claim 6

, wherein

said filter circuit and said bias resistance are mounted on one surface of a printed board, and

said down converter circuit except for said second bias resistance is mounted on the other surface of the printed board.

9. The cable modem tuner according to

claim 1

, wherein

said cut off frequency is set such that the signal of said second frequency band is passed and the signal of said first frequency band is attenuated in said first mode, and that the signals of said first and second frequency bands are passed in said second mode.

10. The cable modem tuner according to

claim 9

, wherein

said filter circuit has

an inductance element passing an output signal of said mixer circuit,

a first capacitance element coupled between said induction element and the ground node, a second capacitance element coupled in parallel with said induction element, and

a switch element provided parallel to said second capacitance element and of which on/off is instructed externally,

said switch element being turned off/on in said first and second modes, respectively.

11. The cable modem tuner according to

claim 1

, further comprising:

an intermediate frequency automatic gain control circuit positioned between said tuner circuit and said down converter circuit adjusting amplitude of the intermediate frequency signal of said first frequency band to a prescribed range; and

a signal converting circuit receiving an output of said down converter circuit and converting to a parallel type signal;

wherein

said cut off frequency is set such that the signal of said second frequency band is passed and the signal of said first frequency band is attenuated in said first mode, and that the signals of said first and second frequency bands are passed in said second mode.

12. The cable modem tuner according to

claim 11

, wherein

said tuner circuit, said intermediate frequency automatic gain control circuit, said down converter circuit and said signal converting circuit are contained in one box.

13. The cable modem tuner according to

claim 1

, further comprising:

an upstream circuit for transmitting a data signal to a cable television station; and

a high pass filter for introducing a multiwave down signal from said cable television station while removing said data signal.

14. The cable modem tuner according to

claim 13

, wherein

said upstream circuit includes

a variable gain amplifying circuit amplifying the data signal to said CATV station with a prescribed gain, and

a coupling circuit coupling an output of said amplifying circuit to an input of said high pass filter.

15. The cable modem tuner according to

claim 13

, wherein

a down data signal of a band different from said multiwave down signal is input from said CATV station to said receiving circuit through a cable, and

said receiving circuit includes a branching circuit branching and outputting said down data signal.

16. The cable modem tuner according to

claim 13

, wherein

said upstream circuit, said tuner, said high pass filter and said down converter are contained in a shield case partitioned individually.