HIGH-FREQUENCY FILTER

• US 20100291946A1
• Filed: 11/25/2008
• Published: 11/18/2010
• Est. Priority Date: 12/03/2007
• Status: Active Grant

• Current Assignee: Panasonic Corporation (Panasonic Holdings Corporation)
• Original Assignee: Panasonic Corporation (Panasonic Holdings Corporation)
• Inventors: Onishi, Keiji, Nakatsuka, Hiroshi, Yamakawa, Takehiko, Okajima, Toshiyuki
• Granted Patent: US 8,306,499 B2
• Time in Patent Office: Days
• US Class Current: 455/454
• CPC Class Codes: H03H 7/0153 Electrical filters; Controlling thereof
• CPC Class Codes: H03H 7/1758 Series LC in shunt or branch path H03H7/1791 takes precedence
• CPC Class Codes: H03H 7/1766 Parallel LC in series path H03H7/1783 takes precedence
• CPC Class Codes: H03H 9/6433 Coupled resonator filters
• CPC Class Codes: H04H 40/18 Arrangements characterised by circuits or components specially adapted for receiving
• CPC Class Codes: H04N 21/41407 embedded in a portable device, e.g. video client on a mobile phone, PDA, laptop constructional details of equipment or arrangements specially adapted for portable computer application G06F1/1626; arrangements specially adapted for mobile receivers in broadcast systems H04H20/57
• CPC Class Codes: H04N 21/426 Internal components of the client ; Characteristics thereof H04N5/44 takes precedence
• CPC Class Codes: H04N 21/42607 for processing the incoming bitstream
• CPC Class Codes: H04N 5/4446 IF amplifier circuits specially adapted for B&W TV RF amplifiers in general H03F3/189
• CPC Class Codes: H04N 7/102 Circuits therefor, e.g. noise reducers, equalisers, amplifiers H04N7/108 takes precedence

Abstract

A digital television broadcast receiving section (100) of a mobile telephone terminal includes an antenna (101), a notch filter (102), a low-pass filter (LPF) (103), a low noise amplifier (LNA) (104), a receiving IC (105), a control section (107), and an input section (108). A passband for digital television broadcast is divided into several parts. The control section (107) switches a characteristic of each of the notch filter (102) and the LPF (103) so as to combine filters appropriate for a low-band channel or a high-band channel. Thus, frequencies in a mobile telephone transmission frequency band of the mobile telephone terminal, and frequencies in a band of other systems, the frequencies in these band being interfering waves, are largely attenuated, and at the same time, frequencies in the passband which is a frequency band for digital television broadcast are allowed to pass with low loss.

Claims

1. A high-frequency filter whose passband is a predetermined frequency band for digital television broadcast, and whose stopband is a mobile telephone terminal transmission band which is near to the passband, the high-frequency filter comprising:

a notch filter including;

a first characteristic having predetermined pass loss in the passband, and having a predetermined attenuation amount in the stopband; and

a second characteristic having a passband which is included in the predetermined frequency band and is narrower than the predetermined frequency band, and having, in the stopband, an attenuation amount larger than the predetermined attenuation amount;

a low-pass filter including;

a first characteristic which has an attenuation pole set to be near to the stopband, and thereby has an attenuation amount larger than the predetermined attenuation amount; and

a second characteristic which has an attenuation pole set to be distant from the stopband, and thereby has, in the passband which is the predetermined frequency band, pass loss smaller than the predetermined pass loss; and

a control section which, if a channel selected by a user is a low-band channel that is within the passband and on a lower-frequency side of a threshold frequency in the passband, operates the notch filter and the low-pass filter by combining the first characteristic of the notch filter and the first characteristic of the low-pass filter, and if the channel selected by the user is a high-band channel that is within the passband and on a higher-frequency side of the threshold frequency, operates the notch filter and the low-pass filter by combining the second characteristic of the notch filter and the second characteristic of the low-pass filter.

2. The high-frequency filter according to claim 1, wherein the high-band channel is equal to or higher than a channel, a frequency three times as large as a local frequency of the channel being coincide with a frequency in a frequency band of 1710 to 1785 MHz used in a mobile telephone system.

3. The high-frequency filter according to claim 1, wherein the low-band channel is equal to or lower than a channel, a frequency three times as large as a local frequency of the channel being coincide with a frequency in a frequency band of 1477 to 1501 MHz used in a mobile telephone system.

4. The high-frequency filter according to claim 1, wherein an intermediate frequency is sufficiently low for a local frequency of the selected channel to be substantially equal to a frequency of a desired wave.

5. The high-frequency filter according to claim 1, wherein

the high-band channel is equal to or higher than a channel, a frequency three times as large as a local frequency of the channel being coincide with a frequency in a frequency band of 1710 to 1785 MHz used in a mobile telephone system,

the low-band channel is equal to or lower than a channel, a frequency three times as large as a local frequency of the channel being coincide with a frequency in a frequency band of 1477 to 1501 MHz used in a mobile telephone system, and

an intermediate frequency is sufficiently low for a local frequency of the selected channel to be substantially equal to a frequency of a desired wave.

6. The high-frequency filter according to claim 1, wherein frequency bands including frequencies equal to integral multiples of frequencies of respective desired waves of the low-band channel and the high-band channel are attenuated.

7. The high-frequency filter according to claim 1, wherein the notch filter

includes

a plurality of piezo resonators including at least one ezo resonator, and

a reactance device connected in parallel to the at least one series piezo resonator, and

obtains the first characteristic and the second characteristic by changing a reactance value of the reactance device.

8. The high-frequency filter according to claim 1, wherein the low-pass filter

includes a plurality of inductors and a plurality of capacitors which cause LC resonance, and

obtains the first characteristic and the second characteristic by changing capacitance values of the plurality of capacitors.

9. The high-frequency filter according to claim 7, wherein the reactance device value is changed by a switch being switched to a connected state or an unconnected state.

10. The high-frequency filter according to claim 7, wherein the reactance device is formed by a capacitor.

11. A communication apparatus comprising:

an antenna transmitting and receiving a high-frequency signal;

a filter attenuating, among received signals, a signal having a frequency other than a channel frequency;

a low noise amplifier amplifying a faint signal obtained by the filter; and

a digital television receiving circuit section demodulating a received signal amplified by the low noise amplifier,

wherein the high-frequency filter according to claim 1 is applied to the filter.