CN101262290A - Fm tuning circuit - Google Patents
Fm tuning circuit Download PDFInfo
- Publication number
- CN101262290A CN101262290A CNA2008100824612A CN200810082461A CN101262290A CN 101262290 A CN101262290 A CN 101262290A CN A2008100824612 A CNA2008100824612 A CN A2008100824612A CN 200810082461 A CN200810082461 A CN 200810082461A CN 101262290 A CN101262290 A CN 101262290A
- Authority
- CN
- China
- Prior art keywords
- circuit
- agc
- initial point
- action
- frequency
- 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.)
- Pending
Links
Images
Landscapes
- Noise Elimination (AREA)
- Superheterodyne Receivers (AREA)
- Circuits Of Receivers In General (AREA)
- Television Receiver Circuits (AREA)
Abstract
The invention provides a FM tuning circuit which can avoid noise generated by a redivious audio frequency when a minitype computer switches a pre-set value of AGC circuit through a communication line. In the FM tuning circuit, a squelch circuit (15) for applying squelch to an audio frequency circuit is provided for a path of an audio frequency signal generated by receiving broadcast signal for outputting hopeful wave to the audio frequency circuit backwards. Exterior minitype computer (4) communicates with an AGC circuit (16) through a communication line (5) for switching an initial point of AGC action to a high-frequency amplifier (2). When the minitype computer (4) switches the initial point of AGC action, the squelch circuit (15) and switching time of the initial point of the AGC action can realize squelching synchronously by providing squelch signal to the squelch circuit (15).
Description
Technical field
The present invention relates to the FM tuning circuit that audio circuit is connected in back segment.
Background technology
Present FM broadcast singal is with the configuration of the frequency interval of 100KHz, and in the area of the adjacent existence in Duo Jia broadcasting station of output highfield signal, will produce interference signal on the 100KHz front-back direction being separated by with the broadcast singal in want broadcasting station.In order to reduce the influence of above-mentioned interference signal, taked to produce the decay mode of gain of AGC voltage and suppressed the level of the interference signal that produced by interference signal.
Fig. 5 is the circuit structure diagram of FM tuning circuit in the past.
The input section of FM tuning circuit is provided with high-frequency circuit 21, and this high-frequency circuit 21 is made of adjustable damping circuit 21a, input tuning circuit 21b, high-frequency amplifier circuit 21c and the inter-stage tuning circuit 21d of input FM broadcast singal.High-frequency amplifier circuit 21c is made of variable-gain amplification circuit.
The output of inter-stage tuning circuit 21d is connected on the mixting circuit 22, and oscillating circuit 23 provides the change local oscillation signal that frequency is used to mixting circuit 22.I.F. tuning circuit 24, first band pass filter 25, intermediate frequency amplifier circuit 26, second band pass filter 27 and the 3rd band pass filter 28 are connected on the back segment of mixting circuit 22.I.F. tuning circuit 24 is made of transformer (IFT-intermediate frequency transformer), and first to the 3rd band pass filter 25,27,28 is made of ceramic filter.And though the mid-band frequency of I.F. tuning circuit 24, first to the 3rd band pass filter 25,27,28 is 10.7MHz, the bandwidth of I.F. tuning circuit 24 is about 500KHz, and the bandwidth of band pass filter 25,27,28 is about 200KHz.
Outlet side at inter-stage tuning circuit 21d is provided with an AGC voltage generation circuit 29, and at the outlet side of I.F. tuning circuit 24 the 2nd AGC voltage generation circuit 30 is set.Export AGC voltage respectively from each AGC voltage generation circuit 29,30, and this AGC voltage is input to superposing circuit 31 jointly.By superposing circuit 31 overlapping two AGC voltages, and wherein high-power AGC voltage offers adjustable damping circuit 21a and high-frequency amplifier circuit 21c.
The frequency characteristic of the AGC voltage that the one AGC voltage generation circuit 29 is exported mainly relies on the frequency characteristic of inter-stage tuning circuit 21d, and the frequency characteristic of the 2nd AGC voltage that the 2nd AGC voltage generation circuit 30 is exported mainly relies on the frequency characteristic of I.F. tuning circuit 24.And, the frequency characteristic of the frequency characteristic of tuning circuit 21d and I.F. tuning circuit 24 between comparative degree, the frequency broad (broad) of inter-stage tuning circuit 21d, and the frequency of I.F. tuning circuit 24 point (sharp).
At above-mentioned FM tuning circuit, in the scope of answering the hundreds of KHz of receiving broadcast signal (for example 500KHz), when investigating by concerning between the AGC voltage that input signal obtained, the 2nd AGC voltage is greater than an AGC voltage; And signal is when exceeding its scope, and an AGC voltage is greater than the 2nd AGC voltage.
Therefore, in the scope of answering receiving broadcast signal frequency Fb 500KHz, the incoming signal level when the incoming signal level in beginning AGC when action being lower than begin the AGC action by an AGC voltage by the 2nd AGC voltage.In contrast, in the scope that has surpassed 500KHz from frequency Fb, the incoming signal level when just the incoming signal level in beginning AGC when action being higher than begin the AGC action by the 2nd AGC voltage by an AGC voltage.
By the way, the interference signal of the 2nd AGC voltage about to the 100KHz of strong electric field region implemented the AGC action, and the gain of attenuate high frequency circuit 21 reduces to disturb.In order further to reduce to disturb, as long as improve the level of the 2nd AGC voltage and significantly the gain of attenuate high frequency circuit 21 just can, but take this method also can suppress to be input to the level of answering receiving broadcast signal of mixting circuit 22, also worsen noise characteristic when sensitivity is descended, therefore on the basis of taking into account interference and receiving sensitivity, set the level of the 2nd AGC voltage.And, for the above high reject signal of hundreds of KHz of being separated by (for example 500KHz), will implement the AGC action by an AGC voltage.
Patent documentation 1:(Japan) spy opens the 2003-218711 communique
In recent years, the main circuit that plays till the audio circuit leading portion from the back segment of high-frequency circuit 21 is made of integrated circuit, and from the microcomputer of outside by communication line (for example, I
2The C bus) can set the set point (initial value) of agc circuit.
But, receive when action when switching the set point of AGC action initial point of agc circuit by microcomputer, noise takes place and the problem of tonequality deterioration when having the set point of switching agc circuit in sound signal.
Summary of the invention
The present invention proposes in view of above problem, and its purpose is to provide a kind of FM tuning circuit, even from the set point of microcomputer by communication line switching agc circuit, also can prevent to produce the phenomenon of noise in reproducing audio frequency, and can realize high tone quality.
FM tuning circuit of the present invention is characterised in that to possess: high-frequency circuit, input FM broadcast singal; Agc circuit can and be controlled the gain of above-mentioned high-frequency circuit from the initial point of external setting-up AGC action according to the output signal of above-mentioned high-frequency circuit; And squelch circuit, be arranged on the path of the sound signal that receiving broadcast signal generated of the audio circuit of back segment output expectation ripple and and implement noise elimination above-mentioned audio circuit, and, when external control circuit communicates the initial point that switches the AGC action by communication line and above-mentioned agc circuit, according to the purified signal that this control circuit provides to above-mentioned squelch circuit, synchronously implement noise elimination with the switching time of AGC action initial point.
According to said structure, can adopt the miniaturization that comes implement device by the structure of the set point of communication line switching agc circuit by control circuit, and when control circuit and agc circuit communicate the initial point that has switched the AGC action, synchronously implement noise elimination with the switching time of AGC action initial point, therefore in the set point of switching agc circuit just can by noise elimination eliminate and sound signal overlapping noise, thereby can realize high tone quality.
And the feature of above-mentioned FM tuning circuit of the present invention also is, makes during the noise elimination of above-mentioned purified signal the following time reciprocal for the peak frequency of audio frequency range.
According to said structure, by making during the noise elimination the following time reciprocal for the peak frequency of audio frequency range, even the part of sound signal is eliminated by noise elimination, the people acoustically also is identified as sound into harmony, thereby can prevent the tonequality deterioration that noise elimination causes.
In the above-mentioned FM tuning circuit, above-mentioned high-frequency circuit can by amplifying circuit with and/or attenuator circuit constitute.
And the feature of above-mentioned FM tuning circuit of the present invention also is, the set point of the AGC action initial point of above-mentioned agc circuit, and when the incoming level of expectation ripple during less than threshold value, the initial point of AGC action switches to the postponement side; When the incoming level of expectation ripple during greater than threshold value, the initial point of AGC action switches to side in advance.
According to said structure, when the incoming level of expectation ripple during less than threshold value, because the initial point of AGC action switches to the postponement side, cause so can prevent to comprise near the decay expectation ripple of expect ripple, that cause by high-frequency circuit to be suppressed to make and expect that ripple is suppressed and the state that can't receive.And, when the incoming level of expectation ripple during, because the initial point of AGC action switches to side in advance, so the interference signal with expectation phase of wave adjacency of can decaying effectively greater than threshold value.
In the above-mentioned FM tuning circuit, the set point of the initial point of the AGC of above-mentioned agc circuit action is switched to when postponing side, the initial point of postponing the AGC action in the interference level to the expectation ripple is no more than the scope of predetermined value is ideal.
According to the present invention, even, also can prevent from reproducing audio frequency, to produce the phenomenon of noise, and can realize high tone quality from the set point of microcomputer by communication line switching agc circuit.
Description of drawings
Fig. 1 is the structure chart of the involved FM tuning circuit of one embodiment of the present invention.
When Fig. 2 moves initial point for the AGC that has changed high-frequency amplifier according to each incoming level, the figure of expression attenuation characteristic.
Fig. 3 is that the desired S/N value of each incoming level of high-frequency amplifier keeps one regularly, the figure of expression interference level characteristic.
The oscillogram of the sound signal of (a) of Fig. 4 during for the set point of the AGC action initial point that switched agc circuit; (b) be from the oscillogram of microcomputer to the purified signal of squelch circuit output.
Fig. 5 is the structure chart of FM tuning circuit in the past.
Among the figure
1 antenna, 2 high-frequency amplifiers, 3 integrated circuits, 4 microcomputers, 5 communication line (I
2The C bus), 6 frequency mixers, 7 local oscillation circuits, 8,11,13 intermediate frequency amplifiers, 9 ceramic filters, 12 band pass filters, 14 multiplexer, 15 squelch circuits, 16AGC circuit, 17 electric field intensity detectors (S instrument)
Embodiment
Below, describe the specific embodiment of the present invention with reference to the accompanying drawings in detail.
Fig. 1 is the structure chart of the involved FM tuning circuit of one embodiment of the present invention.FM tuning circuit shown in this figure to high-frequency amplifier 2 input FM broadcast singals, changes the frequency of FM broadcast singal that high-frequency amplifiers 2 amplified with integrated circuit 3 from antenna 1, and it is exported to loud speaker (not showing in the accompanying drawing) as sound signal.And, on integrated circuit 3, pass through communication line (for example, I
2The C bus) 5 connect microcomputer 4, thereby can be from the initial point of external setting-up AGC action.
High-frequency amplifier 2 is the high-frequency circuit of the gain-variable of FM tuning circuit, and this FM tuning circuit changes gain by the control signal from integrated circuit 3.As the high-frequency circuit of gain-variable, except that high-frequency amplifier, also can constitute, and as shown in Figure 5, can also make up adjustable damping circuit and high-frequency amplifier circuit by the adjustable damping circuit.
Integrated circuit 3 possesses the frequency mixer 6 that changes the FM broadcast singal frequency that high-frequency amplifier 2 exported.Provide local oscillation signal to frequency mixer 6 from the local oscillation circuit 7 that is located at integrated circuit 3 outsides.After the FM broadcast singal that is become intermediate-freuqncy signal by frequency mixer 6 frequency conversions obtains amplifying by intermediate frequency amplifier 8, be fetched into the outside of integrated circuit 3.Ceramic filter 9 extraction expectation ripple frequency bands by integrated circuit 3 outsides (for example, are imported in the integrated circuit 3 after broadcast singal 10.7MHz) again, and are amplified by intermediate frequency amplifier 8.After band pass filter 12 and intermediate frequency amplifier 13, be input to multiplexer 14 as sound signal.In multiplexer 14, the sound signal about being divided into.From multiplexer 14 exported about sound signal be output to the outside of integrated circuit 3 through squelch circuit 15.
And integrated circuit 3 possesses the agc circuit 16 of the gain of control high-frequency amplifier 2.Agc circuit 16 is introduced the output signal of intermediate frequency amplifier 11 along separate routes, and changes the gain of agc circuit 16 according to the signal level of expectation ripple.AGC action by agc circuit 16 is adjusted into, and makes the signal level as the expectation ripple of the output of intermediate frequency amplifier 11 become the level of wanting.
Agc circuit 16 constitutes, and can change the AGC action initial point to high-frequency amplifier 2 by the control signal of microcomputer 4.And, with the output signal of intermediate frequency amplifier 8 along separate routes and introduce the electric field strength that detects the expectation ripple in the electric field intensity detector (S instrument) 17.The detection signal that electric field intensity detector (S instrument) 17 is exported communicates through the microcomputer 4 of communication line 5 with integrated circuit 3 outsides.Microcomputer 4 is set the initial point of AGC action according to the electric field strength of expectation ripple.By the communication between microcomputer 4 and the agc circuit 16, the initial point of switching controls AGC action.
Secondly, the action of the present embodiment with said structure is described.
In the present embodiment, change the set point of the AGC action initial point of agc circuit 16, make and when expectation ripple signal level is less, postpone the initial point of AGC action and when expecting that the ripple signal level is bigger, do sth. in advance the initial point that AGC moves.And, if postpone the initial point of AGC action, will in the scope that be no more than predetermined value to the interference level of expecting ripple, carry out.
Fig. 2 is, when changing initial point to the AGC action of high-frequency amplifier 2 according to each incoming level (85dBuV, 90dBuV, 95dBuV) of high-frequency amplifier 2, represents the figure of its decay situation.Transverse axis represents that at a distance of in the frequency in the interference broadcast radio station in want broadcasting station, the center of transverse axis (0MHz) is the frequency in the broadcasting station of wanting.The longitudinal axis is represented the level that the disturbed ripple of the expectation ripple in the broadcasting station of wanting suppresses.For example, when beginning the AGC action, be about 4dB from only the be separated by decay of disturbing wave of 0.4MHz of expectation wave direction high frequency side with the incoming level of 85dBuV.In addition, when beginning the AGC action, be about 1dB from only the be separated by decay of disturbing wave of 0.4MHz of expectation wave direction high frequency side with the incoming level of 95dBuV.
As mentioned above, can suppress to expect near the ripple attenuation by the initial point (improving the incoming level of beginning AGC action) of postponing the AGC action.And the initial point (reducing the incoming level of beginning AGC action) by AGC action ahead of time can strengthen near the attenuation the expectation ripple.
Fig. 3 represents, the interference level characteristic when desired S/N reaches certain value (30dB) in each incoming level (85dBuV, 90dBuV, 95dBuV) of high-frequency amplifier 2.Transverse axis is represented at a distance of in the frequency in the interference broadcast radio station in want broadcasting station, and the center of transverse axis (0MHz) is the frequency in the broadcasting station of wanting.The longitudinal axis is represented interference level.For example, when beginning the AGC action,, just do not reach the S/N of expectation if near the expectation ripple, do not reduce interference level with the incoming level of 95dBuV.That is, if do not reduce interference level during the initial point of postponing the AGC action, it is big that the possibility of interference just becomes.And, when beginning the AGC action, even interference level is big to the S/N that to a certain degree also can reach expectation near the expectation ripple with the incoming level of 85dBuV.That is, during the initial point of AGC action ahead of time, even interference level arrives to a certain degree greatly, the possibility of its interference is also very lower.
In present embodiment, consider the interference broadcast radio station near the basis to the attenuation characteristic of AGC action initial point and the interference level characteristic expectation ripple, the initial point that makes the AGC action carries out dynamic change according to the incoming level of expectation ripple.For example, the incoming level of expectation ripple is during less than threshold value, and the initial point of AGC action is set at 90dBuV; And the incoming level of expectation ripple is during greater than threshold value, and the initial point of AGC action is set at 85dBuV.
Set the initial point of the AGC action in the high-frequency amplifier 2 by the way, and will comprise that by high-frequency amplifier 2 the FM broadcast singal of expectation ripple and disturbing wave is adjusted into the prearranged signal level and outputs on the integrated circuit 3.By frequency mixer 6 frequency conversion of FM broadcast singal is predetermined intermediate frequency, and is input to the broadcast singal that extracts expectation ripple frequency band in the ceramic filter 9 by intermediate frequency amplifier 8.Then, be imported into again in the integrated circuit 3, be input to multiplexer 14 through intermediate frequency amplifier 11, band pass filter 12 and intermediate frequency amplifier 13.Here, the sound signal about being divided into offers squelch circuit 15.Squelch circuit 15 receives the purified signal that microcomputers 4 are provided, to about sound signal implement noise elimination and handle.
Fig. 4 (a) is the oscillogram of the sound signal (left side or right) when switching the set point of AGC action initial point of agc circuit 16 according to the indication of microcomputer 4.As shown in the drawing, when the set point of the AGC action initial point that has switched agc circuit 16, switching noise overlaps on the sound signal.When being reproduced by loudspeaker audio, this switching noise broadcasts as noise, therefore needs to eliminate.In the present embodiment, when 4 pairs of agc circuits 16 of microcomputer are set the communication of AGC action initial point, simultaneously also to the purified signal of squelch circuit 15 outputs shown in Fig. 4 (b).Purified signal only be equivalent to call duration time between microcomputer 4 and the agc circuit 16 during in the gate pulse of formation high level.15 of squelch circuits carry out the action of truncated signal output in during the gate pulse of purified signal, and remove switching noise from sound signal.It during the gate pulse peak frequency (for example, the following time reciprocal 20kHz) of audio frequency range.So, eliminated noise and the leakage sound that causes reach the people the sense of hearing the degree that can not discern, thereby can prevent the tonequality deterioration.
As mentioned above, according to present embodiment, when 4 pairs of agc circuits 16 of microcomputer are set the communication of AGC action initial point, simultaneously to squelch circuit 15 output purified signals, block the switching noise that overlaps on the sound signal synchronously with purified signal, therefore, even the set point of AGC action initial point that changes agc circuits 16 from microcomputer 4 by communication line 5 can realize high tone quality also can prevent generating noise.
On the FM tuning circuit of the present invention applicable to the AGC action initial point that switches agc circuit by microcomputer.
Claims (5)
1. a FM tuning circuit is characterized in that,
Possess: high-frequency circuit, input FM broadcast singal; Agc circuit can and be controlled the gain of above-mentioned high-frequency circuit from the initial point of external setting-up AGC action according to the output signal of above-mentioned high-frequency circuit; And squelch circuit, be arranged on the path of the sound signal that receiving broadcast signal generated of the audio circuit of back segment output expectation ripple and and implement noise elimination above-mentioned audio circuit,
And, when external control circuit communicates the initial point that switches the AGC action by communication line and above-mentioned agc circuit,, synchronously implement noise elimination with the switching time of AGC action initial point according to the purified signal that this control circuit provides to above-mentioned squelch circuit.
2. FM tuning circuit according to claim 1 is characterized in that, makes during the noise elimination of above-mentioned purified signal the following time reciprocal for the peak frequency of audio frequency range.
3. FM tuning circuit according to claim 1 is characterized in that above-mentioned high-frequency circuit comprises amplifying circuit and/or attenuator circuit.
4. FM tuning circuit according to claim 1 is characterized in that, the set point of the initial point of the AGC of above-mentioned agc circuit action, and when the incoming level of expectation ripple during less than threshold value, the initial point of AGC action switches to the postponement side; When the incoming level of expectation ripple during greater than threshold value, the initial point of AGC action switches to side in advance.
5. FM tuning circuit according to claim 4 is characterized in that, the set point of the initial point of the AGC of above-mentioned agc circuit action is switched to when postponing side the initial point of postponing the AGC action in the interference level to the expectation ripple is no more than the scope of predetermined value.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2007060465A JP2008227728A (en) | 2007-03-09 | 2007-03-09 | Fm tuner circuit |
| JP060465/2007 | 2007-03-09 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CN101262290A true CN101262290A (en) | 2008-09-10 |
Family
ID=39845838
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CNA2008100824612A Pending CN101262290A (en) | 2007-03-09 | 2008-03-06 | Fm tuning circuit |
Country Status (2)
| Country | Link |
|---|---|
| JP (1) | JP2008227728A (en) |
| CN (1) | CN101262290A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102186132A (en) * | 2010-12-30 | 2011-09-14 | 成都天奥信息科技有限公司 | Digital squelch method |
| CN103457575A (en) * | 2012-06-04 | 2013-12-18 | 半导体元件工业有限责任公司 | Tuning circuit |
-
2007
- 2007-03-09 JP JP2007060465A patent/JP2008227728A/en not_active Withdrawn
-
2008
- 2008-03-06 CN CNA2008100824612A patent/CN101262290A/en active Pending
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102186132A (en) * | 2010-12-30 | 2011-09-14 | 成都天奥信息科技有限公司 | Digital squelch method |
| CN103457575A (en) * | 2012-06-04 | 2013-12-18 | 半导体元件工业有限责任公司 | Tuning circuit |
| CN103457575B (en) * | 2012-06-04 | 2016-08-10 | 半导体元件工业有限责任公司 | Tuning circuit |
Also Published As
| Publication number | Publication date |
|---|---|
| JP2008227728A (en) | 2008-09-25 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| JPH05199134A (en) | Fm receiver | |
| JPH08154061A (en) | Broadcasting signal receiver | |
| CN1938958A (en) | Am reception circuit | |
| CN101262290A (en) | Fm tuning circuit | |
| JP2009088618A (en) | Receiving device | |
| US5523801A (en) | Upper and lower adjacent picture signal traps | |
| JPH0629878A (en) | Radio receiver | |
| US8027652B2 (en) | Radio front end | |
| JPH0198325A (en) | On-vehicle receiver | |
| JP2009224908A (en) | Receiving system for terrestrial digital television | |
| JP2005268841A (en) | Tv receiver | |
| US7386293B2 (en) | Receiving circuit | |
| KR200295550Y1 (en) | Radio Frequency Amplification Circuit | |
| US6405026B1 (en) | Communication device and method | |
| KR20010002675A (en) | Noise attenuation circuit of FM radio by electric field | |
| KR100581176B1 (en) | Apparatus for decreasing electric field noise in case of receiving audio AM small electric field | |
| KR20070071547A (en) | If gain control device of digital tuner | |
| KR200179166Y1 (en) | Circuit for eliminating ghost noise in wireless device | |
| KR100315349B1 (en) | SAW filter drive circuit of digital TV | |
| JPS5945302B2 (en) | Muting system for FM radio receiver | |
| KR19990035192A (en) | Noise Reduction Device for Radio Reception System | |
| JPS623620B2 (en) | ||
| JP2623766B2 (en) | Sound equipment with FM radio | |
| KR20000013598U (en) | Audio volume auto adjuster according to stereo / mono mode | |
| JPH0448059Y2 (en) |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| C06 | Publication | ||
| PB01 | Publication | ||
| C10 | Entry into substantive examination | ||
| SE01 | Entry into force of request for substantive examination | ||
| C02 | Deemed withdrawal of patent application after publication (patent law 2001) | ||
| WD01 | Invention patent application deemed withdrawn after publication |
Open date: 20080910 |