Portable telephone capable of decreasing noise

• US 5,933,769 A
• Filed: 07/11/1997
• Issued: 08/03/1999
• Est. Priority Date: 07/11/1996
• Status: Expired due to Fees

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Kaneko, Yasuhiro
• Primary Examiner(s): Hudspeth, David R.
• Assistant Examiner(s): Chawan, Vijay B.
• Application Number:
  US08/893,452
• Time in Patent Office: 753 Days
• Field of Search: 455/222, 455/296, 455/164.1, 455/220, 455/266, 455/218, 455/166.2, 455/164.2, 455/307, 455/310, 455/340, 455/350, 455/375
• US Class Current: 455/296
• CPC Class Codes: H04M 1/6016 in the receiver circuit
• CPC Class Codes: H04M 1/724 User interfaces specially adapted for cordless or mobile telephones

Abstract

In a portable telephone, a voice filter is connected to an antenna through a receiving circuit. A filter is connected to the voice filter through a switching circuit and filters the voice signal from the voice filter to produce a filtered voice signal. The filter has a first cut-off frequency when the filter is supplied with a first clock signal. The filter has a second cut-off frequency smaller than the first cut-off frequency when the filter is supplied with a second clock signal. A telephone receiver is connected to the filter through an amplifier. A clock generating circuit is connected to the filter and generates the first clock signal when is supplied with a first frequency control signal. The clock generating circuit generates the second clock signal when is supplied with a second frequency control signal. A control circuit supplies the first frequency control signal to the clock generating circuit when a receiving field intensity from the receiving circuit is greater than a first predetermined field intensity. The control circuit supplies the second frequency control signal to the clock generating circuit when the receiving field intensity is between the first predetermined field intensity and a second predetermined field intensity smaller than the first predetermined field intensity. The control circuit supplies a switch control signal to the switching circuit when the receiving field intensity is smaller than the second predetermined field intensity. The switching circuit is off when is supplied with the switch control signal.

Claims

1. A portable telephone comprising:

an antenna for receiving a radio signal to produce a receiving signal;

a receiving circuit connected to said antenna for demodulating said receiving signal to produce a receiving demodulated signal and a receiving field intensity signal;

a voice filter connected to said receiving circuit for filtering said receiving demodulated signal to produce a voice signal;

a switching circuit connected to said voice filter for outputting said voice signal from said voice filter when said switching circuit is not supplied with a switch control signal;

a filter connected to said voice filter through said switching circuit for filtering said voice signal to produce a filtered voice signal, said filter having a first cut-off frequency when said filter is supplied with a first clock signal, said filter having a second cut-off frequency smaller than said first cut-off frequency when said filter is supplied with a second clock signal;

an amplifier connected to said filter for amplifying said filtered voice signal to produce an amplified signal;

a telephone receiver connected to said amplifier for receiving said amplified signal to produce a voice;

a clock generating circuit connected to said filter for generating said first clock signal when said clock generating circuit is supplied with a first frequency control signal and for generating said second clock signal when said clock generating circuit is supplied with a second frequency control signal; and

a control circuit connected to said receiving circuit, said switching circuit, and said clock generating circuit for supplying said first frequency control signal to said clock generating circuit when a receiving field intensity of said receiving field intensity signal is greater than a first predetermined field intensity, for supplying said second frequency control signal to said clock generating circuit when said receiving field intensity of said receiving field intensity signal is between said first predetermined field intensity and a second predetermined field intensity smaller than said first predetermined field intensity, and for supplying said switch control signal to said switching circuit when said receiving field intensity of said receiving field intensity signal is smaller than said second predetermined field intensity.

2. A portable telephone as claimed in claim 1, wherein said portable telephone further comprises an indicating means connected to said control circuit for indicating that said receiving field intensity of said receiving field intensity signal is smaller than said second predetermined field intensity.

3. A portable telephone as claimed in claim 1, wherein said filter comprises a switched capacitor filter.

4. A portable telephone comprising:

an antenna for receiving a radio signal to produce a receiving signal;

a receiving circuit connected to said antenna for demodulating said receiving signal to produce a receiving demodulated signal and a receiving field intensity signal;

a voice filter connected to said receiving circuit for filtering said receiving demodulated signal to produce a voice signal;

a switching circuit connected to said voice filter for outputting said voice signal from said voice filter when said switching circuit is not supplied with a switch control signal;

a filter connected to said voice filter through said switching circuit for filtering said voice signal to produce a filtered voice signal, said filter having a first cut-off frequency when said filter is supplied with a first clock signal, said filter having a second cut-off frequency smaller than said first cut-off frequency when said filter is supplied with a second clock signal;

an amplifier connected to said filter for amplifying said filtered voice signal to produce an amplified signal;

a telephone receiver connected to said amplifier for receiving said amplified signal to produce a voice;

a clock generating circuit connected to said filter for generating said first clock signal when said clock generating circuit is supplied with a first frequency control signal and for generating said second clock signal when said clock generating circuit is supplied with a second frequency control signal;

a control circuit connected to said receiving circuit, said switching circuit, and said clock generating circuit for supplying said first frequency control signal to said clock generating circuit when a receiving field intensity of said receiving field intensity signal is greater than a first predetermined field intensity, for supplying said second frequency control signal to said clock generating circuit when said receiving field intensity of said receiving field intensity signal is between said first predetermined field intensity and a second predetermined field intensity smaller than said first predetermined field intensity, and for supplying said switch control signal to said switching circuit when said receiving field intensity of said receiving field intensity signal is smaller than said second predetermined field intensity, and

setting means connected to control circuit for setting said second frequency control signal in said control circuit.

5. A portable telephone as claimed in claim 4, wherein said portable telephone further comprises an indicating means connected to said control circuit for indicating that said receiving field intensity of said receiving field intensity signal is smaller than said second predetermined field intensity.

6. A portable telephone as claimed in claim 4, wherein said filter comprises a switched capacitor filter.