Digital filter system, carrier reproduction circuit using the digital filter system, and demodulation circuit using the carrier reproduction circuit

A digital filter system comprising:

• conversion means (11) for converting a digital signal, obtained by sampling an analog input signal at a sampling frequency which is N times a carrier frequency, into N signals whose carrier frequencies are substantially zero by selecting said digital signal sequentially;
• N adaptive filters (16 to 19) for filtering the N signals from said conversion means and for changing their own characteristics in accordance with an external signal;
• control means (21) for generating the external signal to control the characteristics of said N adaptive filters based on at least one signal output by said N adaptive filters;
• and
• multiplexing means (22) for multiplexing the output signals of said N adaptive filters, and for outputting a multiplexed signal as a single signal.

A carrier reproduction circuit comprising:

• sampling means (101) for sampling an input signal, including a carrier, at a sampling frequency which is N times a carrier frequency, and for outputting the resultant signal;
• demultiplexer means (11) for cyclically outputting the signal from said sampling means to N systems;
• N adaptive filters (16 to 19) for passing predetermined signal components of each of the N output signals from said demultiplexer means therethrough;
• and
• multiplexer means (22) for multiplexing the outputs of said N adaptive filters, and for outputting a multiplexed signal.

A carrier reproduction circuit comprising:

• sampling means (101) for sampling an input signal, including a carrier, at a sampling frequency which is N times a carrier frequency, and for outputting the resultant signal;
• demultiplexer means (11) for cyclically outputting the signal from said sampling means to N systems;
• N adaptive filters (16 to 19) for passing predetermined signal components of each of the N output signals from said demultiplexer means therethrough;
• multiplexer means (22) for multiplexing the outputs of said N adaptive filters, and for outputting a multiplexed signal;
• delay means (12 to 15) for delaying signals of each of said N systems for attenuating signals having no periodicity by said N adaptive filters;
• subtraction means (20) for obtaining a difference between at least one of the signals output from said N adaptive filters and one of the signals output from said demultiplexer means;
• and
• control means (21) for controlling characteristics of said N adaptive filters based on an output signal of said subtraction means.

A carrier reproduction circuit comprising:

• conversion means (11) for converting a digital signal, obtained by sampling an analog input signal at a sampling frequency which is N times a carrier frequency, into N signals whose carrier frequency is substantially zero, by sequentially outputting said digital signal to N systems;
• N adaptive filters (16 to 19), arranged for said N systems, for filtering input signals;
• and
• output means (22) for sequentially selecting signals output by said N adaptive filters, and for outputting the selected signals as a single signal.

A carrier reproduction circuit comprising:

• sampling means (101) for sampling an input signal, including a carrier, at a sampling frequency which is N times a carrier frequency, and for outputting the resultant signal;
• demultiplexer means (11) for cyclically outputting the signal from said sampling means to N systems;
• N adaptive filters (16 to 19) for passing predetermined signal components of each of the N output signals from said demultiplexer means therethrough;
• multiplexer means (22) for multiplexing the outputs of said N adaptive filters, and for outputting a multiplexed signal;
• a reception circuit (111 to 117) for receiving a radio signal and supplying the received radio signal to said sampling means as the input signal;
• an amplifier (121) for amplifying a carrier output from said multiplexer means (22):
• an adding circuit (123) for generating a signal having an emphasized carrier by adding the carrier amplified by said amplifier to the signal received by said reception circuit;
• and
• means for detecting a signal output from said adding circuit (123).

A digital filter system comprising:

• a demultiplexer which outputs a digital signal, obtained by sampling an analog input signal at a sampling frequency which is N times a carrier frequency, to N systems sequentially;
• N adaptive filters which are arranged for the N systems and which filter the signals output from said demultiplexer;
• and
• a multiplexer which selects the output signals of said N adaptive filters sequentially to output a single signal.

A digital filter system comprising:

• a converter which converts a digital signal, obtained by sampling an analog input signal at a sampling frequency which is N times a carrier frequency, into N signals whose carrier frequencies are substantially zero by selecting said digital signal sequentially;
• N adaptive filters which filter the N signals from said converter and which change their own characteristics in accordance with an external signal;
• a controller which generates the external signal to control the characteristics of said N adaptive filters based on at least one signal output by said N adaptive filters;
• and
• a multiplexer which multiplexes the output signals of said N adaptive filters, and outputs a multiplexed signal as a single signal.

A carrier reproduction circuit comprising:

• a converter which samples an input signal, including a carrier, at a sampling frequency which is N times a carrier frequency, and outputs a resultant signal;
• a demultiplexer which sequentially outputs the signal from said converter to N paths;
• N adaptive filters which pass predetermined signal components of each of the N output signals from said demultiplexer;
• and
• a multiplexer which multiplexes an output of said N adaptive filters, and outputs a multiplexed signal.

A carrier reproduction circuit comprising:

• a converter which converts a digital signal, obtained by sampling an analog input signal at a sampling frequency which is N times a carrier frequency, into N signals whose carrier frequency is substantially zero;
• N adaptive filters each of which filters a respective one of the N signals;
• and
• a selector which sequentially selects signals output from said N adaptive filters, and outputs the selected signals as a single signal.