Composite filter circuit

Claim 2

A composite filter circuit comprising: a resistor having one end to which an input signal is applied; a first series resonant circuit connected to the other end of said resistor, said first series circuit resonating with a first frequency and exhibiting a low-pass filter characteristic; a parallel resonant circuit having a common circuit element which is a constituent part of said first series resonant circuit, said parallel circuit resonating with a second frequency which is higher than said first frequency and exhibiting a frequency-response dip at said second frequency; and a second series resonant circuit connected to said other end of said resistor and in parallel with said first series resonant circuit and parallel resonant circuit, said second series circuit resonating with a frequency which is substantially equal to said second frequency and exhibiting a high-pass or band-pass filtering characteristic, said first series resonant circuit and parallel resonant circuit constituting a low-pass filter circuit for filtering signals of a first specified frequency band, said second series resonant circuit constituting a high-pass or band-pass filter circuit for filtering signals of a second specified frequency band, said low-pass filter circuit section producing an output signal filtered with a low-pass filtering characteristic responsive to the low-pass filtering characteristic of said first series resonant circuit, said filtered output signal having a dip characteristic at said second frequency and frequencies in the neighborhood thereof, and a decreasing characteristic at said second frequency and frequencies in the neighborhood thereof, said high-pass filter circuit producing an output signal filtered with a high-pass or band-pass filtering characteristic responsive to a total of the high-pass or band-pass filtering characteristic of said second series resonant circuit and a decreasing characteristic at said first frequency and frequencies in the neighborhood thereof.

Claim 3

A composite filter circuit as claimed in claim 1 in which said low-pass filter circuit further has a low-pass filter circuit exhibiting a low-pass filtering characteristic wherein the cut-off frequency is a third frequency which is lower than said first frequency and, as a total characteristic, exhibits a generally flat characteristic in the frequency band which is lower than said first frequency, and said high-pass filter circuit further has a high-pass filter circuit exhibiting a high-pass filtering characteristic wherein the cut-off frequency is a fourth frequency which is lower than said second frequency.

Claim 4

A composite filter circuit as claimed in claim 2 and means for picking up and reproducing from a multichannel record disc a multiplexed signal recorded thereon, said recorded signal comprising a direct-wave sum signal having a band of approximately 0 to 15 KHz and an angle-modulated wave difference signal in a band of approximately 20 KHz to 45 KHz which is obtained by angle modulating a carrier wave of 30 KHz with a difference signal, and in which said first and second frequencies are approximately 15 KHz to 30 KHz, respectively; said low-pass filter circuit has a total frequency-response characteristic having a generally flat characteristic in a band of approximately 0 to 15 KHz, a great dip at approximately 30 KHz, and a greatly decreasing characteristic in a band of substantially 15 KHz to 30 KHz; and said high-pass filter circuit has a total frequency-response characteristic having a dip at about 15 KHz and a greatly decreasing characteristic at frequencies below 20 KHz and filtering the band above 20 KHz.

Claim 5

A composite filter circuit as claimed in claim 3 in which said third frequency is approximately 10 KHz, and said fourth frequency is selected at approximately 15 KHz.

Claim 6

A composite filter circuit as claimed in claim 1 and means for picking up and reproducing from a record disc a multiplexed signal recorded thereon, said recorded signal comprising a direct-wave signal in a band substantially equal to said first frequency and an angle-modulated wave signal which is obtained by angle modulating a carrier wave of a frequency equal to said second frequency, and in which said low-pass filter circuit filters said direct-wave signal while said high-pass filter circuit filters said angle-modulated wave signal.

Claim 7

A composite filter circuit comprising: a first resistor to one end of which an input signal is applied; a first series resonant circuit comprising a first coil connected between the other end of said first resistor and a first capacitor, said first resonant circuit resonating with a first frequency, and exhibiting a low-pass filtering characteristic; a second capacitor connected in parallel with said first coil and constituting in conjunction with said first coil a parallel resonant circuit resonating with a second frequency; a low-pass filter circuit comprising a second resistor connected between said first series resonant circuit and a third capacitor, said low-pass filter circuit having a cut-off frequency equal to a third frequency; a second series resonant circuit comprising a fourth capacitor connected to the other end of said first resistor and a second coil, said second resonant circuit resonating with the second frequency, and exhibiting a high-pass or band-pass filtering characteristic; and a high-pass or band-pass filter circuit comprising a fifth capactior connected to said second series resonant circuit and a third resistor, said high-pass or band-pass filter having a cut-off frequency equal to the first frequency, said first series resonant circuit, parallel resonant circuit, and low-pass filter circuit constituting a low-pass filter circuit section for filtering signals of a first specified frequency band, said second series resonant circuit and high-pass or band-pass filter circuit constituting a high-pass or band-pass filter circuit section for filtering signals of a second specified frequency band, said low-pass filter circuit section exhibiting a low-pass filtering characteristic which is generally flat from zero frequency to said first frequency, decreases steeply at frequencies above said first frequency, and has a great dip at said second frequency, said low-pass filtering characteristic resulting from combined effects of the low-pass filter characteristic having a peak at the first frequency of said first series resonant circuit, a dip characteristic at said second frequency of said parallel resonant circuit, a decreasing characteristic at said second frequency due to the existence of said second series resonant circuit, and a low-pass filtering characteristic wherein the cut-off frequency of said low-pass filter circuit is the third frequency, said high-pass filter circuit section exhibiting a high-pass or band-pass filtering characteristic having a dip at said first frequency and a peak at said second frequency resulting from a total of the high-pass filter characteristic having a peak at the second frequency of said second series resonant circuit, the high-pass or band-pass filtering characteristic wherein the cut-off frequency of said high-pass or band-pass filter circuit is the first frequency, and the decreasing characteristic at the first frequency due to the existence of said first series resonant circuit.

Claim 8

A composite filter circuit comprising: a first resistor to one end of which an input signal is applied; a first series resonant circuit comprising a first coil connected between the other end of said first resistor and a first capacitor, said first resonant circuit resonating with a first frequency, and exhibiting a low-pass filtering characteristic; a second capacitor connected in parallel with said first coil and constituting in conjunction with said first coil a parallel resonant circuit resonating with a second frequency; a low-pass filter circuit comprising a second resistor connected between said first series resonant circuit and a third capacitor, said low-pass filter circuit having a cut-off frequency equal to a third frequency; a second series resonant circuit comprising a fourth capacitor connected to the other end of said first resistor and a second coil, said second resonant circuit resonating with the second frequency, and exhibiting a high-pass or band-pass filtering characteristic; and a high-pass or band-pass filter circuit comprising a fifth capactior connected to said second series resonant circuit and a third resistor, said high-pass or band-pass filter having a cut-off frequency equal to the first frequency, said first series resonant circuit, parallel resonant circuit, and low-pass filter circuit constituting a low-pass filter circuit section for filtering signals of a first specified frequency band, said second series resonant circuit and high-pass or band-pass filter circuit constituting a high-pass or band-pass filter circuit section for filtering signals of a second specified frequency band, said low-pass filter circuit section exhibiting a low-pass filtering characteristic which is generally flat from zero frequency to said first frequency, decreases steeply at frequencies above said first frequency, and has a great dip at said second frequency, said low-pass filtering characteristic resulting from combined effects of the low-pass filter characteristic having a peak at the first frequency of said first series resonant circuit, a dip characteristic at said second frequency of said parallel resonant circuit, a decreasing characteristic at said second frequency due to the existence of said second series resonant circuit, and a low-pass filtering characteristic wherein the cut-off frequency of said low-pass filter circuit is the third frequency, said high-pass filter circuit section exhibiting a high-pass or band-pass filtering characteristic having a dip at said first frequency and a peak at said second frequency resulting from a total of the high-pass filter characteristic having a peak at the second frequency of said second series resonant circuit, the high-pass or band-pass filtering characteristic wherein the cut-off frequency of said high-pass or band-pass filter circuit is the first frequency, and the decreasing characteristic at the first frequency due to the existence of said first series resonant circuit.

Claim 9

A composite filter circuit as claimed in claim 6 and means for picking up and reproducing from a multichannel record disc a multiplexed signal recorded thereon of a direct-wave sum signal of a band of approximately 0 to 15 KHz and an angle-modulated wave difference signal of a band of approximately 20 KHz to 45 KHz obtained by angle modulating a carrier wave of 30 KHz responsive to a difference signal, and in which said first, second, and third frequencies are approximately 15 KHz, 30 KHz, and 10 KHz, respectively.