JPH03187624A - Fm tuner - Google Patents

Abstract

PURPOSE:To easily select and judge suitably an IF filter by displaying a spectrum obtained as to an output of the IF filter together with IF level information. CONSTITUTION:The output from a narrow band IF filter 2A or a broad band IF filter 2B is subject to frequency analysis at IF filters 7A-7F and the level of each filter band is detected by level detection circuits 8A-8F as S signal levels S1-S6. A detection circuit 5 detects a detection level signal S0 at the center frequency of a band pass signal from the IF filter 2A or 2B. A microcomputer 4 receives the IF filter passing signal levels S1-S6 and the level signal S0 and applies prescribed processing to display the result of a display device 9. In such a case, the IF filter 2A or 2B is simultaneously displayed. Thus, the selection processing of the optimum IF filter is easily taken by having only to take a glance on the display.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an FM tuner, and more particularly to an FM tuner that facilitates a user's decision to select an appropriate IF filter, either a wideband IF filter or a narrowband IF filter.

(Prior Art) In a conventional FM tuner, a received signal is tuned by the operation of a front end and a PLL circuit, and then subjected to predetermined narrowband or wideband filter processing.
This makes it possible to always play optimal FM broadcasts.

In the above processing, a narrowband filter and a wideband filter are usually provided at the rear of the front end, and these filters are switched and selected by a changeover switch as necessary. That is, the narrowband IF filter is used for long-distance reception where sound quality is not very important, and the wideband IF filter is used for short-distance reception where sound quality is important.

This switching/selection is indicated by lighting up the character display "NARROW" or "WIDE" on the front of the FM tuner.

(Problems to be Solved by the Invention) In recent years, as the number of broadcasting stations has increased, there has been a tendency for the frequency intervals between the frequencies of other broadcasting stations to become closer. For example, in Germany, depending on the region, 200K
Broadcasting station frequencies exist at Hz intervals. When adjacent broadcasting station frequencies approach each other in this way, interference occurs between the tuned frequency signal of the desired broadcasting station received by the FM tuner, and as a result, it becomes difficult to maintain good reception conditions.
The IF filter must be switched frequently, making the operation complicated.

In addition, with conventional FM tuners, the optimal tuning state is set while checking the tuning state display, so when interference occurs due to broadcast signals from broadcasting stations with nearby frequencies as described above, the user can It was necessary to judge the deterioration of the reception tuning state by listening to the deterioration of the reproduced audio and switch the IF filter.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an FM tuner that allows a user to easily select an appropriate IF filter between a wideband IF filter and a narrowband IF filter.

(Means for Solving the Problems) In order to solve the above-mentioned problems, an FM tuner according to the present invention passes intermediate frequency signals of received signals in a narrow band and a wide band, respectively, and uses a narrow band IF filter and a wide band IP filter that are selectively selected. In an FM tuner having a filter, an analysis means for spectral analysis of the output of the narrowband IF filter or the wideband IF filter, and a spectral level obtained by the analysis means for the output of the IF filter selected by the switch, and display means for displaying the IF filter information together with the IF filter information.

(Example) Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of an FM tuner according to the present invention.

The received signal is converted into an intermediate frequency (IF) by selecting a desired broadcasting station frequency at a front end 1 which uses a high frequency amplifier, a mixer, and a local oscillator. This selection (tuning) of the desired broadcasting station frequency is performed using the received signal, which is the input signal of the front end 1, and the output of the detector 5, which is the output signal (output via the microcomputer 4).
This is done through the operation of the LL (phase lock loop) circuit 3. That is, the phase difference between the input and output signals is obtained by the comparator forming the PLL circuit 3, and the local oscillator (usually a VCO is used) in the front end 1 is controlled based on this phase difference to obtain the desired result. Obtains an IF multiplied signal corresponding to the broadcasting station frequency.

The narrowband IF filter 2A and wideband IP filter 2B are
They are respectively centered on the above intermediate frequency (usually 10.7 MHz), and have narrowband IF filters and wideband IF filters, with approximately 100K above and below the center frequency.
This is a filter that allows sideband components distributed with a width of Hz to pass through without being dropped, and blocks other components.

These filters are selected as appropriate based on input (instruction) information from the keys 10. This selection is made by switches SWI and SW2 using a control signal from the microcomputer 4.
This is executed by cooperatively switching.

Further, the output of the narrowband IF filter 2A or the wideband IF filter 2B is frequency-analyzed by the IF filters 7A to 7F, and the level of each filter band is determined by the level detection circuits 8A to 7F.
It is detected as an S signal level at 8F and sent to the microcomputer 4.

That is, the IF filters 7A to 7F each have a capacity of 100K.
Hz bandwidth, centered on the center frequency (10.7 MHz), IF filter 7C is +100 KHz, IF filter 7B is +200 KHz, IF filter 7A is
is +300KHz, IF filter 7D is -1100KHz
, the IF filter 7E has a center frequency shifted by 1200 Kl-1z, the IF filter 7F has a center frequency shifted by 1300 KHz, and a bandwidth of 100 KHz.

The level detection circuits 8A to 8F receive filter outputs from the corresponding IF filters of the IF filters 7A to 7F, respectively, detect the levels, and detect signal levels Sl to S6.
is output to the microcomputer 4.

The detection circuit 5 includes two narrowband IF filters or a wideband I
The FM signal that has passed through the F filter 2B is detected and the audio signal is extracted. This detection is performed, for example, by a method such as PLL detection or pulse count detection.

The detection circuit 5 also detects the detection level signal S0 signal of the center frequency f0 of the bandpass signal from the narrowband IF filter 2A or the wideband IF filter 2B, and the M signal indicating the deviation of the receiving frequency with respect to the broadcasting station frequency. Output to microcomputer 4.

The obtained audio signal (composite signal) is processed in a multiplex decoder (stereo demodulator) 6.
The signal is separated into an L (left) signal and an R (right) signal as a stereo signal and output.

The microcomputer 4 controls the PLL circuit 3, the changeover switches SWI and SW2 between the narrowband IF filter 2A and the wideband IF filter 2B, the display 9, etc. based on input information from various keys 10.

More specifically, the microcomputer 4 has a frequency of 1 with respect to the center frequency output from the level detection circuits 8A to 8F.
An IF filter passing signal of ±300 KHz shifted by 0.00 KHz and a level signal of the center frequency from the detector 5 are received, subjected to predetermined processing, and displayed on a display 9 on a spectrum analyzer indicator located at the bottom of the tank.

FIG. 2 shows a front view of the operation/display section of the FM tuner according to the present invention.

RF selector indicators 21A and 21B indicate that the selected RF selector switch is
It lights up when the mode is set (TANCE) and when it is set directly (DIRECT).

Tuning mode indicators 22A and 22B are
It lights up according to each selection mode of manual tuning (MANUAL) and automatic tuning (AUTO).

The IF band indicators 23A and 23B light up to indicate that the IF filter selected by the changeover switches SWI and SW2 is the narrow band IF filter 2A "NARROW" or the wide band IF filter 2B "WIDE".

The spectrum analyzer indicator 24 displays the received signal level in each 100 KHz bandwidth above and below the center frequency f, and is a characteristic part of the present invention, the details of which will be described later.

The selector indicator 25 is FM, AM.

Displays the band selected with the band selector key on TV, etc.

The frequency display 26 digitally displays the frequency of each channel such as FM, AM, TV, etc.

The main audio/sub audio indicator 27 indicates the output status of the signal to L (left channel) and R (right channel),
When only MAIN is lit, only the MAIN signal is output for both L and R, and when only SUB is lit, only the SUB signal is output for both R.

The bilingual indicator 28 lights up at the TV bilingual broadcast receiving point.

The RECCAL indicator 29 lights up when the recording calibration plate switch is operated.

The stereo indicator 30 lights up when receiving FM or TV stereo broadcasts.

Memory indicator 31 is for selecting any preset station key.

The program indicator 32 lights up when the program switch is activated.

Preset function memory channel 33 is
A/B, 1 to Och stored in memory by the preset station key and preset function key are displayed.

The FM tuner according to the present invention has a display section as shown in FIG. 2 described above, and displays as described below on the spectrum analyzer indicator 24.

In the spectrum analyzer indicator 24 shown in FIG. 2, the horizontal direction indicates a frequency axis, and the vertical direction indicates a level axis. In this example, the frequency axis has a total of seven discrete frequencies f0~
f6 is shown. This discrete frequency corresponds to the IF filters 7A to 7F and the center frequency f in FIG. The vertical level axis corresponds to the signal level S, which is the output of the level detection circuits 8A to 8F at each frequency.
~80 signal levels from S6 and detector 5.

That is, the center frequency f. (10,7MHz) 100K
Frequency fi (fo+100KHz) shifted by Hz
, f2 (fo +200KHz).

f s (f o +300 KHz > , f
4 (f.

100 KHz > , f s (f o 20
0 KHz>, f6 (fo 300KHz) IF filters 7A to 7F with each frequency bandwidth of 100KHz
The (7) S signal level and the 80 signal level from the detector 5 are displayed on the tuning signal indicator 24. Here, the level display in the vertical direction is expressed by the number of lights on in the upward direction of the horizontal line in the figure, and the higher the number of lights on in the upward direction of this line, the higher the level.

In this way, the S level of the received signal in the frequency range of ±300 KHz centered around the center frequency f0 is displayed on the spectrum analyzer indicator 24. At this time, the selected IF filter is also displayed on the IF band indicator 23A or 23B.

Therefore, for example, while using the wideband IF filter 2B, the display on the spectrum analyzer indicator 24 indicates that a broadcast station frequency signal close to the currently tuned broadcast station frequency f0 (in the above example, a frequency signal shifted by +200 KHz) is received. In this case, the S signal level is displayed at a relatively high level in the vertical axis direction at the frequency f2 on the horizontal axis. At this time, the IF band indicator 23B is lit.

As a result, users can check for interference from other broadcasting station frequencies just by looking at this display, and can immediately switch between selector switches SWI and SW2 to select narrowband IP filter 2A, enabling high-quality reception. becomes.

In the embodiment shown in FIG. 2, the output of the narrowband IF filter 2A or wideband IF filter 2B is processed by adding, for example, six hardware circuit configurations of IF filters 7A to 7F and level detection circuits 8A to 8F. .

In FIG. 3, there is another configuration diagram that does not have an IP filter or a level detection circuit that detects the S signal level in a frequency band that deviates from the center frequency, but instead calculates the S signal level based on the signal from the detector 5. is shown as an example.

In this embodiment, the center frequency f. Gara ±30
Search for frequencies in the 0KHz range and find each deviation frequency f0.
The S signal level at f, to f6 is detected.

FIG. 4 shows a flowchart of the processing procedure performed by the microcomputer 4 for searching a predetermined range during tuning. The processing procedure will be explained below.

First, in step S1, the level of the M signal obtained by the detector 5 is compared with a predetermined same value, and if it is equal to or higher than this threshold value, it is determined that there is an out-of-tune state, and an out-of-tune display is performed (step S2). , if it is below the threshold value, it is determined that the state is in synchronization and a synchronization display is performed (step S3>).

Thereafter, in order to reduce errors due to differences in filter characteristics, the narrowband IF filter 2A is forcibly selected by controlling the changeover switches SWI and SW2 (step S4).

Then, the PLL circuit 3 is controlled to shift the tuning frequency from the center frequency f0 by 1300 KHz (step S5).
), by shifting this tuning frequency by 1300 KHz, the first
The functional operation of the IF filter 7F in the figure is performed. The S signal from the detector 5 at this time corresponds to the output signal S6 of the frequency f6 of the level detector 8F in FIG.

The S signal level obtained by the detector 5 is stored in the RAM (Random Access Memory) built in the microcomputer 4.
After being stored in the memory (step S6), the tuning frequency deviation is increased by +1 from -300 KHz to -200 KHz.
00KHz shift (step S7).

It is determined in step S8 whether or not the display tuning frequency shifted by 100 KHz has reached +400 KHz, and if the execution from step S6 to step S8 is repeated until it reaches +400 KHz, a total of seven 100
Tuning frequencies fb, fs, fa, fo shifted by KHz
, f3·f2·f, the signal level S6. S9.
S4°So, Si, S2, and S+ will be stored in the RAM.

In step S8, the display tuning frequency deviation is +400
When the frequency reaches KHz, it is determined that the search for the frequency components necessary for display is completed, and the narrowband filter that was forcibly selected in step S4 is set by the user by controlling the changeover switches SWI and SW2. Switch to the original IF filter side (step 5I).
O).

Furthermore, in step S11, it is determined whether the selected IF switch is the wideband IF filter 2B, and if it is determined that the narrowband IF filter 2A is selected instead of the wideband IF filter 2B, For the S signal level with a frequency deviation of ±100 KHz, the display level is lowered by -2 and displayed. This "°-2" means that two lines arranged in the vertical direction in FIG. 2 that should originally be turned on are turned off. Similarly frequency deviation ±200
The display levels of KHz and ±300 KHz are lowered by -4 and -6, respectively, and displayed (step 512).

On the other hand, if it is determined that the wideband IF filter 2B is selected, -1,
The display level is lowered by -2° for ±200KHz and -3 for ±300KHz (step 8).
13) The adjustment of the display level in steps S12 and 313 is for displaying a level that takes into account the difference in filter characteristics of the wideband/narrowband IF filters.

(Effects of the Invention) As explained above, in this invention, together with information on the selected wideband IF filter or narrowband IF filter, reception in a predetermined frequency range near the tuning frequency (center frequency) for each IF filter is achieved. Since the S signal level of the signal is displayed as a spectrum analyzer, if the broadcast station frequency of another station is close to the currently tuned station frequency, the S signal level of the other station frequency will be displayed together with the selected IF filter information. Therefore, the user can easily select the optimal IF filter just by looking at these displays.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the FM tuner according to the present invention, FIG. 2 is a front view of the FM tuner, and FIG.
The figure is a configuration block diagram showing another embodiment of the FM tuner in this embodiment, and the fourth factor is a flowchart showing the processing procedure for obtaining and displaying S signal levels of a plurality of shift frequencies in the embodiment shown in FIG. It is. 1... Front end, 2A... Narrowband IF filter, 2B... Wideband IF filter, 3... PLL circuit,
4... Microcomputer, 5... Detection circuit, 6
...Multiplex decoder, 7A to 7F...IF filter, 8A to 8F...Level detection circuit, 9...Display unit, 1
0...Key 23A...Narrowband IF filter selection indicator, 23B...
・・Wideband IP filter selection indicator, 24・・Spare indicator

Claims (1)

[Claims] In an FM tuner that passes an intermediate frequency signal of a received signal in a narrow band and a wide band, respectively, and has a narrow band IF filter and a wide band IF filter that are selectively selected,
analysis means for spectral analysis of the output of the narrowband IF filter or wideband IF filter; and displaying the spectral level obtained by the analysis means for the output of the switched and selected IF filter together with the switched and selected IF filter information. An FM tuner comprising: display means.