GB2225681A - Audio filter using multiple input SAW device - Google Patents
Audio filter using multiple input SAW device Download PDFInfo
- Publication number
- GB2225681A GB2225681A GB8926168A GB8926168A GB2225681A GB 2225681 A GB2225681 A GB 2225681A GB 8926168 A GB8926168 A GB 8926168A GB 8926168 A GB8926168 A GB 8926168A GB 2225681 A GB2225681 A GB 2225681A
- Authority
- GB
- United Kingdom
- Prior art keywords
- audio
- filters
- filter
- tuner
- circuit
- Prior art date
- 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.)
- Granted
Links
Classifications
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03J—TUNING RESONANT CIRCUITS; SELECTING RESONANT CIRCUITS
- H03J5/00—Discontinuous tuning; Selecting predetermined frequencies; Selecting frequency bands with or without continuous tuning in one or more of the bands, e.g. push-button tuning, turret tuner
- H03J5/24—Discontinuous tuning; Selecting predetermined frequencies; Selecting frequency bands with or without continuous tuning in one or more of the bands, e.g. push-button tuning, turret tuner with a number of separate pretuned tuning circuits or separate tuning elements selectively brought into circuit, e.g. for waveband selection or for television channel selection
- H03J5/242—Discontinuous tuning; Selecting predetermined frequencies; Selecting frequency bands with or without continuous tuning in one or more of the bands, e.g. push-button tuning, turret tuner with a number of separate pretuned tuning circuits or separate tuning elements selectively brought into circuit, e.g. for waveband selection or for television channel selection used exclusively for band selection
- H03J5/244—Discontinuous tuning; Selecting predetermined frequencies; Selecting frequency bands with or without continuous tuning in one or more of the bands, e.g. push-button tuning, turret tuner with a number of separate pretuned tuning circuits or separate tuning elements selectively brought into circuit, e.g. for waveband selection or for television channel selection used exclusively for band selection using electronic means
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N5/00—Details of television systems
- H04N5/44—Receiver circuitry for the reception of television signals according to analogue transmission standards
- H04N5/46—Receiver circuitry for the reception of television signals according to analogue transmission standards for receiving on more than one standard at will
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N5/00—Details of television systems
- H04N5/44—Receiver circuitry for the reception of television signals according to analogue transmission standards
- H04N5/60—Receiver circuitry for the reception of television signals according to analogue transmission standards for the sound signals
Abstract
The audio IF filter circuit described is suitable for use in a television receiver for decoding audio signals transmitted in any of a number of frequency standards. The circuit includes a tuner (1), first and second audio saw filters (2,3), a third audio saw filter (4), a video saw filter (5), and an audio IF demodulator (6). The tuner (1) supplies signals in parallel to the saw filters (2 to 5) and one of the audio filters is activated by control signals (Va to Vc) so as to give a desired filtering frequency depending on the frequency standard in use. The output signal of the activated one of the saw filters is supplied to the demodulator (6). The third audio saw filter is specially adapted so as to have first and second inputs (4a, 4b) which are connected to the tuner (1) by selection circuitry (Q1, D1, D2, L2, R1 to R3) for selecting one or other of the inputs (4a or 4b) in response to one of the control signals (Va). This allows the third audio saw filter to perform the function of two conventional such filters, thereby reducing the manufacturing cost of the filter circuit. <IMAGE>
Description
C Y -1- AUDIO IF FILTER CIRCUIT The present invention relates to an audio
IF(intermediate frequency) filter circuit, particularly but not necessarily exclusively as applied to a multistandard (multi-system) television receiver.
Such circuits are used to filter out an audio component from television signals. Since various broadcasting systems presently in use have different frequency standards, it is necessary for a filter circuit used in a multi-standard receiver to be able to work with a number of different such standards. Circuits with this ability are known per se, but they suffer from the drawbacks that they contain a large number of elements and are consequently expensive to produce, as well as having asymmetrical operating characteristics which impair operating efficiency.
According to the present invention, there is provided an audio IF circuit for a television receiver, comprising: a tuner; a set of audio filters having respective different frequency characteristics, connected in parallel to receive an output signal from the tuner; and a demodulator connected to receive an output signal from the set of filters, wherein the filters are independently selectable by control signals to provide desired filtering; characterised in that at least one of the filters is provided with multiple inputs each giving a different frequency characteristic, the multiple inputs being connected to receive the output signal from the tuner via selection circuitry responsive to one of the control signals to select one of the multiple inputs.
An embodiment of the present invention can provide an audio IF filter circuit, suitable for use in a television receiver for decoding audio signals transmitted in any of a number of frequency standards. The circuit includes a tuner, first and second audio ( 1 saw (surface-acoustic-wave) filters, a third audio saw filter, a video saw filter, and an audio IF demodulator. The tuner supplies signals in parallel to the saw filters and one of the audio saw filters is activated by control signals so as to give a desired filtering frequency depending on the frequency standard in use. The output signal of the activated one of the saw filters is supplied to the demodulator. The third audio saw filter is specially adapted so as to have first and second inputs which are connected to the tuner by selection circuitry for selecting one or other of the inputs in response to one of the control signals. This allows the third audio saw filter to perform the function of two conventional such filters, thereby reducing the manufacturing cost of the filter circuit.
In a preferred embodiment, the outputs of the respective filters are coupled to each other via diodes and connected to the input of an audio multi IF demodulator via a capacitor and simultaneously connected to the collector of a transistor, whose base is connected to receive a control signal via a diode.
In embodiments of the invention, the load on the tuner is lessened, the frequency characteristic and efficiency of the saw filter are improved, and the structure of the circuit is simplified and the cost reduced. Reference will now be made, by way of example, to the accompanying drawings in which:30 Fig. 1 shows an audio IF filter circuit for a multi-standard television receiver, embodying the present invention; Fig. 2 is a table for explaining operation of the circuit of Fig. 1; 35 Fig. 3 shows a known type of audio IF filter circuit; and 1 ( 1 Fig. 4 is a table for explaining operation of the circuit of Fig. 3.
Before explaining the present invention, a known audio IF filter circuit will first be described with reference to Figures 3 and 4.
In a known type of audio IF filter for a multistandard (multi-system) television receiver illustrated in Fig. 3, the outputs IF1,IF2 of a tuner 31, connected via a coil L, are connected in parallel to the inputs of four audio saw (surface-acoustic-wave) filters 32-35 and a video IF saw filter 36. Emitter-earthed transistors Ql-Q4 are provided whose bases receive control signals Vl-V4 and whose collectors are connected to the outputs of the audio saw filters 32-35. The collectors are also connected to the base of a transistor Q5 through respective diodes Dl-D4 and the input of an audio IF demodulator 37 is connected to the emitter of transistor Q5.
There are many standards or systems in use for audio frequencies in television signals, such as "BG/H","M","L","L"', "D/K", and "I" systems. In the known filter circuit, the selection of one of these decided by the control signals VI-V4 applied to the bases of transistors Ql-Q4. If the standard audio frequency is "BG/H" system for example, the control signals Vl-V3 are "High" as shown in Fig. 4 and the control signal V4 is "Low". This causes transistors QI-Q3 to be turned "on" and the outputs of saw filters 32-34 to become ground voltage. The transistor Q4 is turned "off" and the output of saw filter 35 is applied to the base of transistor Q5 through diode D4, and consequently the buffer transistor Q5 is operated to supply the voltage applied to the resistor R10 connected to the transistor Q5 to the audio IF demodulator 37.
Accordingly only the audio frequency of 33.4 MHz outputted through saw filter 35 from the output signal of the tuner 31, is supplied to the audio IF demodulator 37.
When the standard frequency is "M" system, the control signals Vl,V3,V4 applied to the bases of transistors Ql,Q3,Q4 are "High", the control signal V2 applied to the base of transistor Q2 becomes "Low", and consequently saw filter 33 is selected and the audio frequency of 34.4. MHz is outputted.
When the standard frequency is "L" or "D/V or "I" system, the control signals Vl,V2,V4 applied to the bases of transistors QI,Q2,Q4 are "High", and'the control signal V3 applied to the base of transistor Q3 becomes "Low", and accordingly saw filter 34 is selected and the audio frequency of 32.4MHz is outputted.
When the standard frequency is "L"' system, as explained above the saw filter 32 is-selected and the audio frequency of 40.9MHz is selected In the above type of circuit, five saw filters 32 36 are connected to one tuner 31 so that the load on the tuner is large, the output of tuner 31 is reduced and impedance matching becomes difficult. In addition, since one of the output terminals of each of the saw filters 32-35 is grounded, and the other output terminal is connected to the base of.transistor Q5, this leads to defects, for example, asymmetrical operating characteristics which deteriorate the efficiency by about 6dB. Moreover,production of such a circuit is expensive because of the large number of elements in the circuit.
An embodiment of the present invention will now be described with reference to Figures I and 2.
As shown in Fig. 1, a circuit embodying the invention comprises a tuner 1, audio saw filters 2-4, a video saw filter 5 and an audio IF demodulator 1 J 6. The outputs IF1,IF2 of tuner I are connected to respective input terminals 4a,4b of audio saw filter 4, which input terminals are mutually connected via backto-back diodes Dl,D2. Simultaneously, the output IF1 is connected to the collector of an emitter-earthed transistor Ql, the base of which receives a control signal Va. The connection point between the diodes Dl,D2 at the filter 4 inputs is connected to the power supply Vs. One side of the output terminals of the audio saw filter 4 is connected to a negative input terminal of the audio IF demodulator 6 through a capacitor -C3 and simultaneously connected to the collector of an emitter-earthed transistor Q2.
Diodes D3 to D5 respectively are connected across the outputs of audio saw filters 2-4, the commonlyconnected cathodes of diodes D3,D4 being earthed through a resistor R8. A control signal Vc is connected to the positive input terminal of the audio IF demodulator 6 and simultaneously a control signal Vb is applied to the output of audio saw filters 3,4 via the connecting point between diodes D4 and D5. Control signals Vb,Vc are applied to the base of transistor Q2 through reverse diodes D7,D8 respectively.
The operation of the circuit will now be described with reference to Fig. 2.
The audio saw filter 2 has a frequency characteristic such as to pass 34. 4MHz signals, the audio saw filter 3 has a frequency characteristic Which passes 33.4MHz and the audio saw filter 4 can pass both 40.9MHz and 32.4MHz, depending on which of its input terminals is used. The control signals Va,Vb,Vc act as switching signals to select one of the audio saw filters 2-4 and when appropriate one of the input terminals 4a or 4b.
Accordingly, when the standard audio frequency is "BG/H" system, the control signals Va,Vb,Vc become ( A "High", "Low"s "High", as shown in Fig. 2 and consequently diodes Dl,D3, D7 are turned "on", diodes D2,D4,D8 are turned "off", and the transistor Q2 is turned "off". In other words, diodes D3,D5 are turned 'ton". the diodes D4 is turned "off" and, since the values of resistors R6-R9 are selected to be sufficiently large, an alternating current component signal is inputted into the audio IF demodulator 6 through capacitor C4, diode D3, audio saw filter 3, and diode D5 and capacitor C3 to select the frequency of 33.4MHz through the audio saw filter 3.
When the standard audio frequency is "M" system, the control voltage Va, Vb are "High" and the control voltage Vc. is "Low"; accordingly, the diodes D1,D4,D8 are turned "on" and the diodes D2,D3,D7 are turned 11off", and the diode D5 is turned flonfl, Therefore the signal is applied to the audio IF demodulator 6 through capacitor C4, audio saw filter 2, diodes D4,D5 and capacitor C3 to give a frequency characteristic of 34.4MHz.
When the standard audio frequency is "L" system, the control signals Va, Vb,Vc are "High" mode, the diodes D1,D3,D4 are turned "on" and the diodes D2,D7,D8 are turned "off" to make transistor Q2 turned flon1r.
Consequently the diode D5 is turned "off", the input signal is applied through capacitor C1, diode D1, the input terminal 4b of audio saw filter 4 and capacitor C2, and therefore the output signal is supplied to the audio IF demodulator 6 through capacitor C4, diodes D3,D4, and the audio saw filter 4 and capacitor C3, to give the frequency characteristic of 32.4MHz.
When the standard audio frequency is "L"' system, the control signals Va, Vb,Vc become "Low","High","High" respectively, and therefore the diodes D2,D3,D4 are turned "on" and the diodes D1,D5 are turned "off". In this case, the input signal is applied through the 1 capacitor Cl, the input terminal 4a of audio saw filter 4, diode D2 and capacitor C2 and the output signal flows in the same loop as the standard signal in the 'V' system to give the frequency characteristic of 5 40. 9MHz.
Finally, when the standard audio frequency is "D/C or "I" system, the control signals Va,Vbjc are all "High", and the signals are outputted in the same configuration when the standard frequency is "L" system to produce a frequency characteristic of 32.4MHz.
As described above, a circuit embodying the present invention has the merits of improving the frequency characteristics with a small number of audio saw filters in the tuner, thereby reducing the cost.
While there has been described what is at present considered to be the preferred embodiment of the invention, it will be understood that various modifications may be made therein within the scope of the appended claims. For example, although the audio IF circuit of the present invention is suitable for use In a television receiver, it may also be possible to usefully apply it in other ways.
c 1
Claims (6)
- CLAIMS: 1. An audio IF circuit for a television receiver, comprising: atuner; a set of audio filters having respective different frequency characteristics, connected in parallel to receive an output signal from the tuner; and a demodulator connected to receiv e an output signal from the set of filters, wherein the filters are independently selectable by control signals to provide desired filtering; characterised in that at least one of the filters is provided with multiple inputs each giving a different frequency characteristic, the multiple inputs being connected to receive the output signal from the tuner via selection circuitry responsive to one of the control signals to select one of the multiple inputs.
- 2. An audio IF circuit as claimed in claim 1, wherein only one of the audio filters has said multiple inputs and wherein there are three audio filters in total.
- 3. An audio IF circuit as claimed in claim 1 or 2, further comprising a video filter connected in parallel with the audio filters to receive the output signal from the tuner.
- 4. An audio IF circuit as claimed in claim 1, 2, or 3, wherein the filters are surfaceacoustic-wave (saw) filters.
- 5. An audio IF circuit as claimed in claims 1 to 4 in combination further comprising first and second emitter-earthed transistors (Q1,Q2), first to eighth diodes (D1... D8), first to fourth capacitors (Cl... C4), and a resistor (R8), and wherein said one audio filter (4) has two input terminals (4a,4b); wherein first and second outputs (IF1,IF2) of the tuner (1) are connected to one of the two input terminals (4a,4b) of said one audio filter (4) and simultaneously the first output (IF1) is connected to the collector of the emitterearthed transistor (Q1) whose base receives a first b control signal (Va), the other one of the input terminals (4a,4b) of said one audio filter (4), connected to the first and second diodes (Dl,D2) at both terminals, is connected to a power supply line (Vs), one side of an output terminal of said one audio filter (4) is connected to a negative input terminal of the demodulator (6) through the third capacitor (0) and simultaneously connected to the collector of the second emitter-earthed transistor (Q2), the outputs of the audio filters (2-4) are connected to the third to fifth diodes (D3- D5) and the cathodes of the third and fourth diodes (D3,D4) are earthed through the resistor (R8), and a third control signal (Vc) is connected to a positive input terminal of the demodulator (6) through the fourth capacitor (C4) and simultaneously a second control signal (Vb) is connected to the outputs of said one audio filter and another of the audio filters (3) and the control signals (Vc,Vb) are applied to the base of the second transistor (Q2) through the seventh and eighth diodes (D7,D8) respectively.
- 6. An audio IF circuit for a television receiver, substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.Pub 5hed 1990 at The Patent Office, State House, 66 71 High Holborn. London WC1R 4TP_ Further copies maybe obtained from The patent Office Sales Branch, St MaIT Cray. Orpington, Kent BR5 ZRD Printed by Mu2tp2ex technioues Itd St Ma:S, Cray. Kent. CCn 1 87
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| KR880018917 | 1988-11-22 |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB8926168D0 GB8926168D0 (en) | 1990-01-10 |
| GB2225681A true GB2225681A (en) | 1990-06-06 |
| GB2225681B GB2225681B (en) | 1993-04-14 |
Family
ID=19281519
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8926168A Expired - Fee Related GB2225681B (en) | 1988-11-22 | 1989-11-20 | Audio if filter circuit |
Country Status (6)
| Country | Link |
|---|---|
| DE (1) | DE3938303A1 (en) |
| ES (1) | ES2017569A6 (en) |
| GB (1) | GB2225681B (en) |
| HU (1) | HU206173B (en) |
| IT (2) | IT8934897V0 (en) |
| RU (1) | RU1833515C (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE4317220A1 (en) * | 1993-05-24 | 1994-12-01 | Thomson Brandt Gmbh | Circuit for sound standard detection in a television receiver |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3858118A (en) * | 1973-07-17 | 1974-12-31 | Westinghouse Electric Corp | Acoustic surface wave television tuner |
| EP0196130A2 (en) * | 1985-03-16 | 1986-10-01 | Philips Patentverwaltung GmbH | Circuit arrangement for the input stages of a television tuner |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FI63508C (en) * | 1981-02-11 | 1983-06-10 | Salora Oy | KOPPLING VID EN TELEVISIONSMOTTAGARE FOER DETEKTERING AV LJUDSIGNALER SOM SAENTS ENLIGT OLIKA SAENDNINGSNORMER |
| US4511924A (en) * | 1982-10-29 | 1985-04-16 | Rca Corporation | Frequency translation phase-locked loop for separate or intercarrier type television sound detection |
-
1989
- 1989-11-17 HU HU895954A patent/HU206173B/en not_active IP Right Cessation
- 1989-11-17 DE DE3938303A patent/DE3938303A1/en active Granted
- 1989-11-20 ES ES898903952A patent/ES2017569A6/en not_active Expired - Lifetime
- 1989-11-20 GB GB8926168A patent/GB2225681B/en not_active Expired - Fee Related
- 1989-11-21 RU SU894742485A patent/RU1833515C/en active
- 1989-11-21 IT IT34897U patent/IT8934897V0/en unknown
- 1989-11-21 IT IT04688689A patent/IT1237577B/en active IP Right Grant
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3858118A (en) * | 1973-07-17 | 1974-12-31 | Westinghouse Electric Corp | Acoustic surface wave television tuner |
| EP0196130A2 (en) * | 1985-03-16 | 1986-10-01 | Philips Patentverwaltung GmbH | Circuit arrangement for the input stages of a television tuner |
| US4756024A (en) * | 1985-03-16 | 1988-07-05 | U.S. Philips Corporation | RF-input circuit arrangement for a television tuner |
Also Published As
| Publication number | Publication date |
|---|---|
| DE3938303A1 (en) | 1990-05-23 |
| RU1833515C (en) | 1993-08-07 |
| IT8946886A0 (en) | 1989-11-21 |
| GB2225681B (en) | 1993-04-14 |
| DE3938303C2 (en) | 1992-12-24 |
| IT1237577B (en) | 1993-06-08 |
| ES2017569A6 (en) | 1991-02-16 |
| HUT55179A (en) | 1991-04-29 |
| IT8934897V0 (en) | 1989-11-21 |
| GB8926168D0 (en) | 1990-01-10 |
| IT8946886A1 (en) | 1991-05-21 |
| HU206173B (en) | 1992-08-28 |
| HU895954D0 (en) | 1990-02-28 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 20071120 |