GB2246676A - Stereo/mono fm tuner with noise suppression - Google Patents
Stereo/mono fm tuner with noise suppression Download PDFInfo
- Publication number
- GB2246676A GB2246676A GB9107414A GB9107414A GB2246676A GB 2246676 A GB2246676 A GB 2246676A GB 9107414 A GB9107414 A GB 9107414A GB 9107414 A GB9107414 A GB 9107414A GB 2246676 A GB2246676 A GB 2246676A
- Authority
- GB
- United Kingdom
- Prior art keywords
- output
- tuner
- amplifier
- offset voltage
- level detector
- 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
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/06—Receivers
- H04B1/16—Circuits
- H04B1/1646—Circuits adapted for the reception of stereophonic signals
- H04B1/1661—Reduction of noise by manipulation of the baseband composite stereophonic signal or the decoded left and right channels
- H04B1/1669—Reduction of noise by manipulation of the baseband composite stereophonic signal or the decoded left and right channels of the demodulated composite stereo signal
Landscapes
- Engineering & Computer Science (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Stereo-Broadcasting Methods (AREA)
- Circuits Of Receivers In General (AREA)
- Noise Elimination (AREA)
Description
cjE, e,'7 (S FM TUNER_ This invention relates to an improvement of an FM
tuner which performs its original high fidelity signal reception when the strength of the electric field is high, and which, as the antenna input level decreases, perf orms an automatic separation function of smoothly switching a stereophonic signal reception over to a monaural signal reception, an automatic high cut function of decreasing high frequency noises, and a soft mute function of decreasing a reproduction output; i.e., so-called automatic reception control functions (hereinafter referred merely as "ARC functions", when applicable).
When an FM radio wave is received, its electric field strength is greatly affected, for instance, by the concerned geographical features, buildings and the distance between the FM broadcast station and the FM signal receiving point. In order to overcome this difficulty, the FM tuner has the above-described ARC functions (cf. Japanese Utility Model Examined Publication No. Sho. 59-31077).
The technical concept disclosed by the Japanese Utility Model Examined Publication No. Sho. 59-31077 will be described with reference to Fig. 3.
In Fig. 3, reference numeral 1 designates an antenna; 2, a front end; 3, an IF amplifier; 4, a detector; 5, a multiplexer; 1 - 1 1 6, an S meter detector for detecting the level of the output signal of the IF amplifier 3; 7, a separation control circuit which, when it becomes impossible to perform the stereophonic signal reception because the output level of the S meter detector 6 decreases slightly, operates to switch the operation mode of the multiplexer 5 to the monaural mode; 8, a high cut circuit which, when the output level of the S meter detector 6 is further decreased, operates to high-cut the output of the multiplexer 5; and 9, a soft mute circuit which, when the 10 output level of the S meter detector 6 is further decreased, operates to decrease the output level of the IF amplifier 3.
In the FM tuner thus organized, as the antenna input level decreases, the automatic separation function, the automatic high cut function and the soft mute function are continuously is performed, so that the signal is reproduced with high fidelity while the noises are effectively reduced.
On the other hand, in the case of the above- described ARC functions, the system is greatly fluctuated in total gain. In order to absorb the fluctuation, it is necessary to provide a number of adjusting points therein.
The number of adjusting points may be decreased by the following method: As shown in Fig. 3, a gain adjusting IF amplifier 31, which is variable enough to absorb the total gain f luctuation is connected between the front end 2 and the IF amplifier 3.
A 1 1 1 i 1 1 1 1 i i i i i i 1 In practice, the gain adjusting IF amplifier 31, needs a range of variation of at least 10 dB. Therefore, an amplifier comprising a field-effect transistor or a transistor cannot satisfy the requirement completely. Accordingly, the circuit is unavoidably intricate, and high in manufacturing cost.
On the other hand, in a recent FM tuner, the IF amplifier 3, the detector 4 and the multiplexer 5 are, in general, provided as integrated circuits which are different chips. Therefore, the chips are non-uniform in fluctuation.
Accordingly, even if the total gain is adjusted, it is impossible to completely eliminate the fluctuation.
is Accordingly, an object of this invention is to eliminate the abovedescribed difficulties accompanying a conventional PM tuner. More specifically, an object of the invention is to provide an PM tuner in which various control circuits controlled by the S meter output and the S meter output voltage are low in manufacturing cost and can be adjusted at only one point.
The foregoing object has been achieved by the provision of an PM tuner according to the invention. The specific feature of the PM tuner resides in that a level detection is carried out to detect the IF output, and an adjustable DC offset voltage is added to the level detection output, to provide a DC 3 offset output, which is utilized for controlling the ARC functions.
In the accompanying drawings:- Fig. 1 is a block diagram showing one embodiment of an FM -5 tuner according to this invention; Fig. 2 is a graphical representation indicating S meter outputs with respect to input levels in an offset voltage adder; and Fig. 3 is a block diagram showing a conventional FM tuner.
One preferred embodiment of this invention is shown in Fig. 1, in which those parts which have been previously described with reference to Fig. 3 are'designated by the same reference numerals.
An FM tuner according to the invention is different from the abovedescribed conventional tuner (Fig. 3) in that the level of the electric field strength of the received signal is detected by detecting the output signal of the IF amplifier 3 with an IF level detector 11, whose output is applied to an offset voltage adder 12 with a gain adjusting resistor 12a in order to provide an offset output which is utilized for controlling the ARC functions including various functions.
The operation of the FM tuner thus organized will be described.
- 4 i 1 i 1 1 1 i i 1 1 1 i is The output of the IF amplifier 3 is detected by the IF level detector 11, to provide a DC output (S meter output). In the of f set voltage adder 12, the DC output of the IF level detector 11 is offset by adjusting the variable resistor 12a.
More specifically, as shown in Fig. 2, when the DC output (S meter output) is high, it is decreased by adjusting the variable resistor 12a as indicated by the arrow A; and when the DC output is low, it is increased as indicated by the arrow B; that is, the DC output is maintained constant by adjusting the variable resistor 12a. Thus, in the integrated circuits, the total gain fluctuation of the system is adjusted.
The output of the offset voltage adder 12 is utilized for controlling the ARC functions such as the automatic separation function, the automatic high cut function, and the soft mute function. Thus, even if the system total gain is fluctuated, the control can be achieved positively by only one adjustment operation.
As was described above, in the PM tuner of the invention, the IF level output proportional to the electric field strength is not directly used, and instead the ARC functions are controlled using the offset voltage adjusted at one point. Therefore, it is unnecessary for the PM tuner to employ an intricate expensive gain adjustable amplifier. Accordingly, the PM tuner can be provided at a low manufacturing cost, and can be applied to systems which utilize the S meter output in such a manner that the offset voltage is utilized for 1 1 temperature correction or switching the sensitivity in automatic broadcast selection.
- 6 z i 1 i 1 i i 1 1 1 i i 1 i i f 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
Claims (9)
1 1 1
2 1 2 1 4 5 1 2 3 1 2 3 2. The FM tuner as def ined in claim 1, wherein said 2 amplifier is an intermediate frequency amplifier.
3. The FM tuner as def ined in claim 1, wherein said 2 output means comprises a multiplexer.
4. The FM tuner as def ined in claim 2, wherein said level detector is an intermediate frequency level detector.
The FM tuner as def ined in claim 4, wherein said level detector provides a DC output.
6. The PM tuner as defined in claim 5 further comprising a variable resistor coupled to said offset voltage adder, and wherein said DC output of said level detector is adjusted by said offset voltage adder in accordance with a resistance of said variable resistor.
7. The FM tuner as def ined in claim 6, wherein. said variable resistor is adjusted such that the output of said offset voltage adder is maintained constant.
8. The FM tuner as defined in claim 6, wherein each of said separation control, high cut and soft mute circuits is an integrated circuit.
9. An FM tuner substantially as described with reference to Figures 1 and 2 of the accompanying drawings.
Published 1992 at The Patent Office, Concept House. Cardiff Road. Newport, Gwent NP9 1RH. Further copies may be obtained from Sales Branch, Unit 6. Nine Mile Point, Cwmfelinfach. Cross Keys. Newport, NP1 7HZ. Printed by Multiplex techniques ltd. St Mary Crky. Kent.
W w i 1 i 1
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP7110290U JPH0429244U (en) | 1990-07-05 | 1990-07-05 |
Publications (3)
Publication Number | Publication Date |
---|---|
GB9107414D0 GB9107414D0 (en) | 1991-05-22 |
GB2246676A true GB2246676A (en) | 1992-02-05 |
GB2246676B GB2246676B (en) | 1994-06-15 |
Family
ID=13450849
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
GB9107414A Expired - Fee Related GB2246676B (en) | 1990-07-05 | 1991-04-09 | FM Tuner |
Country Status (3)
Country | Link |
---|---|
JP (1) | JPH0429244U (en) |
DE (1) | DE4111709C2 (en) |
GB (1) | GB2246676B (en) |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP1931058A1 (en) * | 2005-09-28 | 2008-06-11 | Pioneer Corporation | Diversity reception device |
Families Citing this family (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE19542738A1 (en) * | 1995-11-16 | 1997-05-22 | Bayerische Motoren Werke Ag | Switching arrangement for mobile radio receivers |
DE19630392C2 (en) * | 1996-07-26 | 1998-10-01 | Sgs Thomson Microelectronics | Stereo decoder with smooth transition between stereo operation and mono operation |
Family Cites Families (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPS539403A (en) * | 1976-07-14 | 1978-01-27 | Pioneer Electronic Corp | Fm stereophonic receiver |
JPS5931077Y2 (en) * | 1979-05-07 | 1984-09-04 | パイオニア株式会社 | fm stereo receiver |
JPS5931077A (en) * | 1982-08-13 | 1984-02-18 | Mitsubishi Electric Corp | Semiconductor light emitting device |
US4691357A (en) * | 1985-06-14 | 1987-09-01 | Pioneer Electronic Corporation | Stereophonic receiving circuit providing improved switching characteristics between stereophonic and monaural modes |
US4727580A (en) * | 1986-04-23 | 1988-02-23 | Alpine Electronics, Inc. | Radio receiver |
JPH01162020A (en) * | 1987-12-18 | 1989-06-26 | Nec Ic Microcomput Syst Ltd | Fm radio receiver |
-
1990
- 1990-07-05 JP JP7110290U patent/JPH0429244U/ja active Pending
-
1991
- 1991-04-09 GB GB9107414A patent/GB2246676B/en not_active Expired - Fee Related
- 1991-04-10 DE DE19914111709 patent/DE4111709C2/en not_active Expired - Fee Related
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP1931058A1 (en) * | 2005-09-28 | 2008-06-11 | Pioneer Corporation | Diversity reception device |
EP1931058A4 (en) * | 2005-09-28 | 2010-06-16 | Pioneer Corp | Diversity reception device |
Also Published As
Publication number | Publication date |
---|---|
DE4111709C2 (en) | 1994-06-09 |
DE4111709A1 (en) | 1992-01-16 |
GB2246676B (en) | 1994-06-15 |
JPH0429244U (en) | 1992-03-09 |
GB9107414D0 (en) | 1991-05-22 |
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Legal Events
Date | Code | Title | Description |
---|---|---|---|
746 | Register noted 'licences of right' (sect. 46/1977) |
Effective date: 19950601 |
|
PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 19970409 |