GB1572478A – Electrical filter circuits
– Google Patents
GB1572478A – Electrical filter circuits
– Google Patents
Electrical filter circuits
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Publication number
GB1572478A
GB1572478A
GB2063977A
GB2063977A
GB1572478A
GB 1572478 A
GB1572478 A
GB 1572478A
GB 2063977 A
GB2063977 A
GB 2063977A
GB 2063977 A
GB2063977 A
GB 2063977A
GB 1572478 A
GB1572478 A
GB 1572478A
Authority
GB
United Kingdom
Prior art keywords
sin
wrt
circuit
frequency
cos
Prior art date
1978-05-26
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
GB2063977A
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
British Aircraft Corp Ltd
Original Assignee
British Aircraft Corp Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
1978-05-26
Filing date
1978-05-26
Publication date
1980-07-30
1978-05-26
Application filed by British Aircraft Corp Ltd
filed
Critical
British Aircraft Corp Ltd
1978-05-26
Priority to GB2063977A
priority
Critical
patent/GB1572478A/en
1980-07-30
Publication of GB1572478A
publication
Critical
patent/GB1572478A/en
Status
Expired
legal-status
Critical
Current
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Classifications
H—ELECTRICITY
H03—ELECTRONIC CIRCUITRY
H03D—DEMODULATION OR TRANSFERENCE OF MODULATION FROM ONE CARRIER TO ANOTHER
H03D7/00—Transference of modulation from one carrier to another, e.g. frequency-changing
H03D7/16—Multiple-frequency-changing
H—ELECTRICITY
H03—ELECTRONIC CIRCUITRY
H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
H03H19/00—Networks using time-varying elements, e.g. N-path filters
H—ELECTRICITY
H03—ELECTRONIC CIRCUITRY
H03D—DEMODULATION OR TRANSFERENCE OF MODULATION FROM ONE CARRIER TO ANOTHER
H03D7/00—Transference of modulation from one carrier to another, e.g. frequency-changing
H03D7/16—Multiple-frequency-changing
H03D7/161—Multiple-frequency-changing all the frequency changers being connected in cascade
H03D7/163—Multiple-frequency-changing all the frequency changers being connected in cascade the local oscillations of at least two of the frequency changers being derived from a single oscillator
H—ELECTRICITY
H03—ELECTRONIC CIRCUITRY
H03D—DEMODULATION OR TRANSFERENCE OF MODULATION FROM ONE CARRIER TO ANOTHER
H03D7/00—Transference of modulation from one carrier to another, e.g. frequency-changing
H03D7/16—Multiple-frequency-changing
H03D7/165—Multiple-frequency-changing at least two frequency changers being located in different paths, e.g. in two paths with carriers in quadrature
Description
(54) IMPROVEMENTS RELATING TO ELECTRICAL FILTER
CIRCUITS
(71) We, BRITISH AIRCRAFT COR
PORATION, a British Company, of Filton
House, Bristol BS99 7AR, do hereby declare the invention, for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement:- The invention relates to electrical filter circuits.
In radio-frequency and radar receivers and transmitters an often desirable feature is the ability to filter out unwanted signals without imposing restrictions upon the receiver’s or transmitter’s frequency range.
According to one aspect of the present invention a radio frequency filter includes a first single-sideband mixing circuit for converting a radio frequency signal to a predetermined intermediate frequency, a filter circuit operative at that intermediate frequency, and a second single-sideband mixing fruit for reconverting the signal from the intermediate frequency being equal to the initial radio frequency.
In the preferred form, the local oscillator signal is provided by a voltage controlled oscillator and the first and second singlesideband mixing circuits each comprise two beat frequency generators. In the first single-sideband mixing circuit, the two beat frequency generators are each connected to receive differently phased signals from the
RF input and differently phased signals from the local oscillator. In the second singlesideband mixing circuit, the two beat frequency generators are each connected to receive differently phased signals from the output of the filter circuit following the first single-sideband mixing circuit, and differently phased signals from the local oscillator.
In order that the invention may be better understood, one example will now be described with reference to the accompanying drawing, which is a functional block diagram of a radio frequency filtering circuit.
In the drawing, the radio frequency filter essentially comprises three stages. These are a mixing-down single-sideband mixer 1, a band pass filter 2 and a mixing-up singlesideband mixer 3.
The single-sideband mixer 1 receives the radio frequency input signal and also a local oscillator signal provided by a voltagecontrolled oscillator 16, which may receive its voltage input from a surveillance unit 17, for example.
In the mixer 1, the radio frequency signal sin wit and the local oscillator sin wrt are applied directly to the respective inputs of a first beat frequency generating circuit 4; these signals are also applied to the input of a second beat frequency circuit 5 through II/2 phase retarding circuits 6 and 7 respectively.
The outputs of the beat-frequency circuits 4 and 5 are connected to the inputs of a summing circuit 8.
Thus, the inputs to circuit 4 are sin wit and sin wrt, the inputs to circuit 5 are -cos wit and -cos wrt, and the output of circuit 8, the intermediate frequency signal, is:- sin wit. sin wrt + (-1)cos wit (-1)cos wrt = cos (wi -Wr)t, that is a signal proportional to the frequency difference between the radio frequency and local oscillator signals.
This intermediate frequency from the summing circuit 8 is applied to the intermediate frequency filter 2.
In the second single-sideband mixer 3 the filtered intermediate frequency signal and modified local oscillator signal are supplied directly to the appropriate inputs of a third beat frequency generating circuit 9, and to the corresponding inputs of a fourth beat frequency circuit 10 through further II/2 phase retarding circuits 11 and 12 respectively. The outputs of the beat frequency circuits 9 and 10 are connected to the inputs of another summing circuit 13, the output of which is the re-converted and filtered radio frequency signal. The local oscillator signal is modified by inversion in inverting amplifier 14 and by phase retarding in II/2 phaseretarding circuit 15; thus where the original local oscillator signal is proportional to sin wit the modified signal is proportional to cos wrt. This modified oscillator signal is further modified by the phase retarding circuit 12 referred to above before application to the beat frequency generating circuit 9.
Thus denoting the intermediate frequency signal and the modified local oscillator signal by cos(wi – wr)t and cos wrt respectively then: if wi > wr, the inputs to circuit 9 are cos(wi -Wr)t and sin wrt, the inputs to circuit 10 are sin(wi–wr)t and cos wrt, and the output of circuit 13, the reconverted radio frequency signal is sin wrt(sin wit. sin wrt + cos wrt. cos wrt) + cos wrt (sin wit. cos wrt –sin wrt cos wit)
= sin2 wrt. sin wit + cos2 wrt. sin wit
= sin wit
and if Wr > Wi, the inputs to circuit 9 are cos(wr -wi)t and sin wrt, the inputs to circuit 10 are – sin(wr wi)t and cos wrt, and the output of circuit 13 is
sin wrt (sin wrt. sin wit + cos wit. cos wrt) – cos wrt (sin wrt. cos wit – sin wit. cos wrt)
= sin 2Wrt. sin wit + cos2 wrt. sin wit + cos2wrt. sin wit
= sin wit.
Therefore the frequency of the output
radio frequency signal is always equal to the
frequency of the input radio frequency
signal.
The radio frequency filter is thus able to
filter any radio frequency signal within a
wide frequency band without adjustment to
filter components or filter switching merely
by appropriate adjustment of the local oscil
lator frequency.
Moreover, the radio frequency filter
described has considerable frequency agility
due to the use of a voltage-controlled oscil
lator to provide the local oscillator signal.
The filtered output signal may then be
applied to a frequency measuring circuit, for
example. Thus, by using two single-sideband
generators which are complementary, and a
voltage-controlled oscillator to provide the
local reference frequency, we are able to
“look” at a narrow band of RF frequencies at
a very high speed of selection.
WHAT WE CLAIM IS:
1. A radio frequency filter including a
first single-sideband mixing circuit for con
verting a radio frequency signal to a pre
determined intermediate frequency, a filter
circuit operative at that intermediate fre
quency, and a second single-sideband mixing
circuit for re-converting the signal from the
intermediate frequency to the radio fre
quency, the final radio frequency being equal
to the initial radio frequency.
2. A radio frequency filter including a first single-sideband mixing circuit connected to receive an incoming radio frequency signal, together with the output of a local oscillator and including first and second beat frequency generating circuits, each connected to receive both the radio frequency input signal and the local oscillator signal, the phase of the signals applied to the second beat frequency generating circuit being different from that of the signals applied to the first beat frequency generating circuit, and a summing circuit receiving the outputs of the first and second beat frequency generating circuits and providing an output having a frequency equal to the difference of the input signal frequency and local oscillator frequency; a filter circuit operative at the difference frequency; and a second singlesideband mixing circuit including third and fourth frequency generating circuits each connected to receive the output of the difference frequency filter and the local oscillator signal, the phases of the signals applied to the third beat frequency generating circuit being different from the phases of the signals applied to the fourth beat frequency generating circuit, and a summing circuit connected to receive the outputs of the beat frequency generating circuits, the said signals applied to the beat frequency generating circuits being such that the output of the summing circuit is at the radio frequency of the input signal.
3. A radio frequency filter in accordance with claim 2, in which the first beat frequency generating circuit receives inputs sin wit and sin wrt, respectively, where wi represents the input signal frequency and wr the local oscillator frequency, and the second beat frequency generating circuit receives signals – cos wit and – cos wrt, the summing circuit of the first single sideband mixer providing an output signal represented by cos (Wi -Wr)t.
5. A radio frequency filter in accordance with claim 4, in which in the second single sideband mixer circuit, the third beat frequency generating circuit receives from the first single sideband mixing circuit a signal represented by cos (Wi -Wr)t and from the local oscillator a signal sin wrt; and the fourth beat frequency generating circuit receives from the first single sideband mixing circuit a signal represented by sin (Wi – wr)t and from the local oscillator a signal cos wrt; the summing circuit providing an output represented by sin wit.
6. A single sideband mixing circuit in accordance with any one of the preceding claims, in which the local oscillator signal is generated by a voltage-controlled oscillator.
7. A radio frequency filter, substantially as herein described with reference to the
accompanying drawing.
**WARNING** end of DESC field may overlap start of CLMS **.
Claims (1)
**WARNING** start of CLMS field may overlap end of DESC **.
modified by inversion in inverting amplifier 14 and by phase retarding in II/2 phaseretarding circuit 15; thus where the original local oscillator signal is proportional to sin wit the modified signal is proportional to cos wrt. This modified oscillator signal is further modified by the phase retarding circuit 12 referred to above before application to the beat frequency generating circuit 9.
Thus denoting the intermediate frequency signal and the modified local oscillator signal by cos(wi – wr)t and cos wrt respectively then: if wi > wr, the inputs to circuit 9 are cos(wi -Wr)t and sin wrt, the inputs to circuit 10 are sin(wi–wr)t and cos wrt, and the output of circuit 13, the reconverted radio frequency signal is sin wrt(sin wit. sin wrt + cos wrt. cos wrt) + cos wrt (sin wit. cos wrt –sin wrt cos wit)
= sin2 wrt. sin wit + cos2 wrt. sin wit
= sin wit
and if Wr > Wi, the inputs to circuit 9 are cos(wr -wi)t and sin wrt, the inputs to circuit 10 are – sin(wr wi)t and cos wrt, and the output of circuit 13 is
sin wrt (sin wrt. sin wit + cos wit. cos wrt) – cos wrt (sin wrt. cos wit – sin wit. cos wrt)
= sin 2Wrt. sin wit + cos2 wrt. sin wit + cos2wrt. sin wit
= sin wit.
Therefore the frequency of the output
radio frequency signal is always equal to the
frequency of the input radio frequency
signal.
The radio frequency filter is thus able to
filter any radio frequency signal within a
wide frequency band without adjustment to
filter components or filter switching merely
by appropriate adjustment of the local oscil
lator frequency.
Moreover, the radio frequency filter
described has considerable frequency agility
due to the use of a voltage-controlled oscil
lator to provide the local oscillator signal.
The filtered output signal may then be
applied to a frequency measuring circuit, for
example. Thus, by using two single-sideband
generators which are complementary, and a
voltage-controlled oscillator to provide the
local reference frequency, we are able to
“look” at a narrow band of RF frequencies at
a very high speed of selection.
WHAT WE CLAIM IS:
1. A radio frequency filter including a
first single-sideband mixing circuit for con
verting a radio frequency signal to a pre
determined intermediate frequency, a filter
circuit operative at that intermediate fre
quency, and a second single-sideband mixing
circuit for re-converting the signal from the
intermediate frequency to the radio fre
quency, the final radio frequency being equal
to the initial radio frequency.
2. A radio frequency filter including a first single-sideband mixing circuit connected to receive an incoming radio frequency signal, together with the output of a local oscillator and including first and second beat frequency generating circuits, each connected to receive both the radio frequency input signal and the local oscillator signal, the phase of the signals applied to the second beat frequency generating circuit being different from that of the signals applied to the first beat frequency generating circuit, and a summing circuit receiving the outputs of the first and second beat frequency generating circuits and providing an output having a frequency equal to the difference of the input signal frequency and local oscillator frequency; a filter circuit operative at the difference frequency; and a second singlesideband mixing circuit including third and fourth frequency generating circuits each connected to receive the output of the difference frequency filter and the local oscillator signal, the phases of the signals applied to the third beat frequency generating circuit being different from the phases of the signals applied to the fourth beat frequency generating circuit, and a summing circuit connected to receive the outputs of the beat frequency generating circuits, the said signals applied to the beat frequency generating circuits being such that the output of the summing circuit is at the radio frequency of the input signal.
3. A radio frequency filter in accordance with claim 2, in which the first beat frequency generating circuit receives inputs sin wit and sin wrt, respectively, where wi represents the input signal frequency and wr the local oscillator frequency, and the second beat frequency generating circuit receives signals – cos wit and – cos wrt, the summing circuit of the first single sideband mixer providing an output signal represented by cos (Wi -Wr)t.
5. A radio frequency filter in accordance with claim 4, in which in the second single sideband mixer circuit, the third beat frequency generating circuit receives from the first single sideband mixing circuit a signal represented by cos (Wi -Wr)t and from the local oscillator a signal sin wrt; and the fourth beat frequency generating circuit receives from the first single sideband mixing circuit a signal represented by sin (Wi – wr)t and from the local oscillator a signal cos wrt; the summing circuit providing an output represented by sin wit.
6. A single sideband mixing circuit in accordance with any one of the preceding claims, in which the local oscillator signal is generated by a voltage-controlled oscillator.
7. A radio frequency filter, substantially as herein described with reference to the
accompanying drawing.
GB2063977A
1978-05-26
1978-05-26
Electrical filter circuits
Expired
GB1572478A
(en)
Priority Applications (1)
Application Number
Priority Date
Filing Date
Title
GB2063977A
GB1572478A
(en)
1978-05-26
1978-05-26
Electrical filter circuits
Applications Claiming Priority (1)
Application Number
Priority Date
Filing Date
Title
GB2063977A
GB1572478A
(en)
1978-05-26
1978-05-26
Electrical filter circuits
Publications (1)
Publication Number
Publication Date
GB1572478A
true
GB1572478A
(en)
1980-07-30
Family
ID=10149247
Family Applications (1)
Application Number
Title
Priority Date
Filing Date
GB2063977A
Expired
GB1572478A
(en)
1978-05-26
1978-05-26
Electrical filter circuits
Country Status (1)
Country
Link
GB
(1)
GB1572478A
(en)
Cited By (2)
* Cited by examiner, † Cited by third party
Publication number
Priority date
Publication date
Assignee
Title
EP0060325A1
(en)
*
1981-03-12
1982-09-22
Siemens Aktiengesellschaft
Circuit for the conversion of an input signal, comprising harmonics in a certain frequency domain in an in-phase and/or amplitude-adjustable sinusoidal output signal
US5309162A
(en)
*
1991-12-10
1994-05-03
Nippon Steel Corporation
Automatic tracking receiving antenna apparatus for broadcast by satellite
1978
1978-05-26
GB
GB2063977A
patent/GB1572478A/en
not_active
Expired
Cited By (2)
* Cited by examiner, † Cited by third party
Publication number
Priority date
Publication date
Assignee
Title
EP0060325A1
(en)
*
1981-03-12
1982-09-22
Siemens Aktiengesellschaft
Circuit for the conversion of an input signal, comprising harmonics in a certain frequency domain in an in-phase and/or amplitude-adjustable sinusoidal output signal
US5309162A
(en)
*
1991-12-10
1994-05-03
Nippon Steel Corporation
Automatic tracking receiving antenna apparatus for broadcast by satellite
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Legal Events
Date
Code
Title
Description
1980-10-15
PS
Patent sealed
1980-12-31
732
Registration of transactions, instruments or events in the register (sect. 32/1977)
1981-05-28
732
Registration of transactions, instruments or events in the register (sect. 32/1977)
1985-04-11
746
Register noted ‘licences of right’ (sect. 46/1977)
1989-01-11
PCNP
Patent ceased through non-payment of renewal fee
