Method of controlling filter time constant and filter circuit having the time constant control function based on the method

• US 5,392,456 A
• Filed: 10/03/1990
• Issued: 02/21/1995
• Est. Priority Date: 10/06/1989
• Status: Expired due to Fees

• Current Assignee: Hitachi Kokusai Electric Incorporated (Hitachi, Ltd.)
• Original Assignee: Hitachi, Ltd., Kokusai Electric Co., Ltd.
• Inventors: Tsukamoto, Nobuo, Mitomo, Isamu, Hoshi, Atushi, Noguchi, Hiroshi, Yamakido, Kazuo, Nakagoshi, Arata, Sakaguchi, Jiroh
• Primary Examiner(s): Kuntz, Curtis
• Assistant Examiner(s): FAILE, ANDREW I
• Application Number:
  US07/592,340
• Time in Patent Office: 1,602 Days
• Field of Search: 455/38.2, 455/38.3, 455/307, 455/339, 455/340, 455/70, 455/71, 455/266, 307/520, 307/521, 328/167, 333/17.1, 333/172, 333/174, 340/825.44
• US Class Current: 455/340
• CPC Class Codes: H03H 11/1291 Current or voltage controlled filters

Abstract

A method of controlling the time constant of a filter for use in a radio receiver which receives a signal, transmitted from a transmitting station at a predetermined period, intermittently at the predetermined period and demodulates and delivers the received signal, a filter circuit having the time constant control function based on the method, and a radio receiver having the filter circuit. Preferably, the filter has its time constant switchable stepwise and specifically, parallel connection of capacitors or shortcircuiting of resistors is controlled by turning on/off switches. A controller within the filter circuit or the radio receiver performs control for applying a predetermined periodical signal (or standard pulse signal) to the filter and controlling the time constant of the filter in accordance with an output signal (or triangular pulse) during a first time zone within each operation interval for the intermittent reception and for filtering the signal from the transmitting station and causing a demodulating circuit to demodulate and deliver a filtered signal.

Claims

1. A method of controlling the time constant of a filter operable to intermittently filter an input signal to deliver the same, said filter having means for stepwise switching of the time constant of the filter, comprising the steps of:

inputting to said filter a standard signal having a predetermined frequency and a predetermined signal level during a predetermined interval preceding each filtering operation, said filter including n (n being an integer) elements for changing the time constant, the time constant being switchable stepwise 2ⁿ times;

switching the time constant of said filter by a maximum of n times in accordance with an output signal from said filter; and

performing filtering of the input signal after completion of switching of the time constant of said filter.

2. A method of controlling the time constant of a filter according to claim 1, wherein said predetermined frequency of said standard signal is a frequency in a transient region of the frequency characteristics of said filter.

3. A filter circuit for controlling the time constant of a filter each time that intermittent filtering of an input signal is effected by means of said filter, comprising:

said filter for filtering said input signal, said filter having means for stepwise switching of the time constant of the filter 2ⁿ times by n elements for changing the time constant (n being an integer);

a controller for controlling the time constant of said filter; and

a selector for selectively inputting to said filter either said input signal or a standard signal having a predetermined frequency and a predetermined signal level in response to a command from said controller,

wherein said controller applies said standard signal to said filter in advance of each filtering operation and responds to an output signal from said filter to control the time constant thereof.

4. A filter circuit for controlling the time constant of a filter each time that intermittent filtering of an input signal is effected by means of said filter, comprising:

said filter having means for stepwise switching the time constant of said filter;

a controller for controller the time constant of said filter; and

a selector, responsive to a command from said controller, for selectively inputting to said filter either said input signal or a periodical signal having a predetermined frequency and a predetermined signal level,

wherein said controller applies said periodical signal to said filter in advance of each filtering operation and responds to an output signal from said filter to control the time constant thereof;

wherein said filter includes a plurality of capacitors connectable in parallel under the control of said controller and having a ratio of capacitance between sequential capacitors which is 1;

2, and said controller responds to the output signal from said filter to control sequential connection of said capacitors beginning with a capacitor of a maximum capacitance and ending in a capacitor of a minimum capacitance so as to control the time constant of said filter.

5. A filter circuit for controlling the time constant of a filter each time that intermittent filtering of an input signal is effected by means of said filter, comprising:

said filter having means for stepwise switching the time constant of said filter;

a controller for controlling the time constant of said filter; and

a selector, responsive to a command from said controller, for selectively inputting to said filter either said input signal or a periodical signal having a predetermined frequency and a predetermined signal level,

wherein said controller applies said periodical signal to said filter in advance of each filtering operation and responds to an output signal from said filter to control the time constant thereof;

wherein said filter includes a plurality of resistance elements connected in series and short-circuited under the control of said controller and having a ratio of resistance between sequential resistance elements which is 1;

2, and said controller responds to the output signal from said filter to control sequential short-circuiting of said resistance elements beginning with a resistance element of a maximum resistance and ending in a resistance element of a minimum resistance so as to control the time constant of said filter.

6. A filter circuit for controlling the time constant of a filter each time that intermittent filtering of an input signal is effected by means of said filter, comprising:

said filter for filtering said input signal, said filter having means for stepwise switching of the time constant of said filter 2ⁿ times by n elements for changing the time constant of the filter (n being an integer);

a controller for controlling the time constant of said filter; and

a selector for selectively connecting to said filter either an input line of said input signal or a constant voltage source for causing said filter to generate a triangular wave in response to a command from said controller;

wherein said controller connects said constant voltage source to said filter in advance of each filtering operation and responds to a triangular-wave output signal from said filter to control the time constant thereof.

7. A filter circuit for controlling the time constant of a filter each time that intermittent filtering of an input signal is effected by means of said filter, comprising:

said filter having means for stepwise switching the time constant of said filter;

a controller for controlling the time constant of said filter; and

a selector, responsive to a command from said controller, for selectively connecting to said filter either an input line of said input signal or a constant voltage source for causing said filter to generate a triangular wave;

wherein said controller connects said constant voltage source to said filter in advance of each filtering operation and responds to a triangular wave output signal from said filter to control the time constant thereof

wherein said filter includes a plurality of capacitors connectable in parallel under the control of said controller and having a ratio of capacitance between sequential capacitors which is 1;

2, and said controller responds to the output signal from said filter to control sequential connection of said capacitors beginning with a capacitor of a maximum capacitance and ending in a capacitor of a minimum capacitance so as to control the time constant of said filter.

8. A filter circuit for controlling the time constant of a filter each time that intermittent filtering of an input signal is effected by means of said filter, comprising:

said filter having means for stepwise switching the time constant of said filter;

a controller for controlling the time constant of said filter; and

a selector, responsive to a command from said controller, for selectively connecting to said filter either an input line of said input signal or a constant voltage source for causing said filter to generate a triangular wave;

wherein said controller connects said constant voltage source to said filter in advance of each filtering operation and responds to a triangular wave output signal from said filter to control the time constant thereof;

wherein said filter includes a plurality of resistance elements connected in series and short-circuited under the control of said controller and having a ratio of resistance between sequential resistance elements which is 1;

2, and said controller responds to the output signal from said filter to control sequential short-circuiting of said resistance elements beginning with a resistance element of a maximum resistance and ending in a resistance element of a minimum resistance so as to control the time constant of said filter.

9. A radio receiver for receiving a signal, transmitted from a transmitting station at a predetermined period, intermittently during said period and demodulating and delivering the same, comprising:

a filter for filtering an input signal and having means for stepwise switching of the time constant of the filter 2ⁿ times by n elements for changing the time constant (n being an integer);

a demodulating circuit for demodulating and delivering an output signal from said filter;

a controller for controlling the time constant of said filter; and

an input switching circuit, responsive to a command from said controller, for selectively inputting to said filter either the signal from said transmitting station or a standard signal having a predetermined frequency,

wherein said controller performs control for applying said standard signal to said filter to control the time constant of said filter in accordance with the output signal from said filter during a first time zone within said period and for filtering, demodulating and delivering the signal from said transmitting station during a second time zone after completion of control of the time constant.

10. A radio receiver for receiving a signal, transmitted from a transmitting station at a predetermined period, intermittently during said period and demodulating and delivering the same, comprising:

a filter operable for filtering an input signal and having means for stepwise switching the time constant of said filter;

a demodulating circuit for demodulating and delivering an output signal from said filter;

a controller for controlling the time constant of said filter; and

an input switching circuit responsive to a command from said controller, for selectively inputting to said filter either the signal from said transmitting station or a periodical signal having a predetermined frequency,

wherein said controller performs control for applying said periodical signal to said filter to control the time constant of said filter in accordance with the output signal from said filter during a first time zone within said period and performs control for filtering, demodulating and delivering the signal from said transmitting station during a second time zone after completion of control of the time constant;

wherein said filter includes a plurality of capacitors connectable in parallel under the control of said controller and having a ratio of capacitance between sequential capacitors which is 1;

2, and said controller responds to the output signal from said filter to control sequential connection of said capacitors beginning with a capacitor of a maximum capacitance and ending in a capacitor of a minimum capacitance so as to control the time constant of said filter.

11. A radio receiver for receiving a signal, transmitted from a transmitting station at a predetermined period intermittently during said period and demodulating and delivering the same comprising:

a filter operable for filtering an input signal and having means for stepwise switching the time constant of said filter;

a demodulating circuit for demodulating and delivering an output signal from said filter;

a controller for controlling the time constant of said filter; and

an input switching circuit, responsive to a command from said controller, for selectively inputting to said filter either the signal from said transmitting station or a periodical signal having a predetermined frequency,

wherein said controller performs control for applying said periodical signal to said filter to control the time constant of said filter in accordance with the output signal from said filter during a first time zone within said period and performs control for filtering, demodulating and delivering the signal from said transmitting station during a second time zone after completion of control of the time constant;

wherein said filter includes a plurality of resistance elements connected in series and short-circuited under the control of said controller and having a ratio of resistance between sequential resistance elements which is 1;

2, and said controller responds to the output signal from said filter to control sequential short-circuiting of said resistance elements beginning with a resistance element of a maximum resistance and ending in a resistance element of a minimum resistance so as to control the time constant of said filter.

12. A radio receiver for receiving a signal, transmitted from a transmitting station at a predetermined period, intermittently at said period and demodulating and delivering the same, comprising:

a filter for filtering an input signal and having means for stepwise switching the time constant of said filter 2ⁿ times by n elements for changing the time constant (n being an integer);

a demodulating circuit for delivering after demodulating an output signal from said filter;

a controller for controlling the time constant of said filter; and

a selector, responsive to a command from said controller, for selectively connecting to said filter either an input line of said signal from said transmitting station or a standard signal generated from a constant voltage source for causing said filter to generate a triangular wave,

wherein said controller performs control for applying said standard signal to said filter to control the time constant of said filter in accordance with the triangular wave output signal from said filter during a first time zone within said period and performs control for filtering, demodulating and delivering the signal from said transmitting station during a second time zone after completion of control of the time constant.

13. A radio receiver for receiving a signal, transmitted from a transmitting station at a predetermined period, intermittently at said period and demodulating and delivering the same comprising:

a filter operable for filtering an input signal and having means for stepwise switching of the time constant of said filter;

a demodulating circuit for demodulating and delivering an output signal from said filter;

a controller for controlling the time constant of said filter; and

a selector, responsive to a command from said controller, for selectively connecting to said filter either an input line of said signal from said transmitting station or a standard signal generated from a constant voltage source for causing said filter to generate a triangular wave,

wherein said controller performs control for applying said standard signal to said filter so as to control the time constant of said filter in accordance with the triangular wave output signal from said filter during a first time zone within said period and performs control for filtering, demodulating and delivering the signal from said transmitting station during a second time zone after completion of control of the time constant;

wherein said filter includes a plurality of capacitors connectable in parallel under the control of said controller and having a ratio of capacitance between sequential capacitors which is 1;

2, and said controller responds to the output signal from said filter to control sequential connection of said capacitors beginning with a capacitor of a maximum capacitance and ending in a capacitor of a maximum capacitance so as to control the time constant of said filter.

14. A radio receiver for receiving a signal, transmitted from a transmitting station at a predetermined period, intermittently at said period and demodulating and delivering the same comprising:

a filters operable for filtering an input signal and having means for stepwise switching of the time constant of said filter;

a demodulating circuit for demodulating and delivering an output signal from said filter;

a controller for controlling the time constant of said filter; and

a selector, responsive to a command from said controller, for selectively connecting to said filter either an input line of said signal from said transmitting station or a standard signal generated from a constant voltage source for causing said filter to generate a triangular wave,

wherein said controller performs control for applying said standard signal to said filter so as to control the time constant of said filter in accordance with the triangular wave output signal from said filter during a first time zone within said .period and performs control for filtering, demodulating and delivering the signal from said transmitting station during a second time zone after completion of control of the time constant;

wherein said filter includes a plurality of resistance elements connected in series and short-circuited under the control of said controller and having a ratio of resistance between sequential resistance elements which is 1;

2, and said controller responds to the output signal from said filter to control sequential short-circuiting of said resistance elements beginning with a resistance element of a maximum resistance and ending in a resistance element of a minimum resistance so as to control the time constant of said filter.

15. A radio receiver for receiving a signal, transmitted from a transmitting station at a predetermined period, intermittently at said period and demodulating and delivering the same, comprising:

a filter for filtering an input signal and having means for stepwise switching the time constant of said filter 2ⁿ times by n elements for changing the time constant (n being an integer);

an analog-digital converter for analog-digital conversion of an output signal from said filter;

a demodulating circuit for delivering after demodulating an output signal from said analog-digital converter;

a controller for controlling the time constant of said filter; and

an input switching circuit, responsive to a command from said controller, for selectively inputting to said filter either the signal from said transmitting station or a standard signal having a predetermined frequency,

wherein said controller performs control for applying said standard signal to said filter to control the time constant of said filter in accordance with the output signal from said analog-digital converter during a first time zone within said period and performs control for filtering, demodulating and delivering the signal from said transmitting station during a second time zone after completion of control of the time constant.

16. A radio receiver according to claim 15, wherein said controller includes a standard pulse signal generator for generating said standard signal inputted to said filter, and a reference voltage supplied to said standard signal generator is used in common as a reference voltage supplied to said analog-digital converter.

17. A radio receiver for receiving a signal, transmitted from a transmitting station at a predetermined period, intermittently at said period and demodulating and delivering the same comprising:

a filter operable for filtering and input signal and having means for stepwise switching the time constant of said filter;

an analog-digital converter for analog-digital conversion of an output signal from said filter;

a demodulating circuit for demodulating and delivering an output signal from said analog-digital converter;

.

a controller for controlling the time constant of said filter; and

an input switching circuit, responsive to a command from said controller, for selectively inputting to said filter either the signal from said transmitting station or a periodical signal having a predetermined frequency,

wherein said controller performs control for applying said periodical signal to said filter to control the time constant of said filter in accordance with the output signal from said analog,digital converter during a first time zone within said period and performs control for filtering, demodulating and delivering the signal from said transmitting station during a second time zone after completion of control of the time constant;

wherein said filter includes a plurality of capacitors connectable in parallel under the control of said controller and having a ratio of capacitance between sequential capacitors which is 1;

2, and said controller responds to the output signal from said filter to control sequential connection of said capacitors beginning with a capacitor of a maximum capacitance and ending in a capacitor of a minimum capacitance so as to control the time constant of said filter.