JPH036031Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Field of Industrial Application) The present invention relates to a signal meter circuit for an FM tuner.

(Prior Art) The signal meter of an FM tuner is used to indicate the magnitude of the input signal level. In other words,
When an FM tuner receives an FM broadcast station, the radio waves first transmit the 10.7MHz IF (intermediate frequency).
converted into a signal. Here, when the IF signal is rectified and the DC component is extracted, the signal meter displays the extracted DC component. Thereby, the level of the input signal to the antenna can be detected.

Figure 3 shows the circuit configuration of the signal meter of such an FM tuner.
The radio waves taken in are output to the FM detector 8 through the front end 2, ceramic filters 3 and 4, and limiters 5, 6, and 7.

On the other hand, the signals from limiters 5, 6, and 7 are taken in by level detectors 9, 10, and 11, and then added by an adder 12. This addition output is transmitted to the signal meter drive circuit 13 and the level setting circuit 14.
is supplied to

The signal meter 15 receives a drive signal from the signal meter drive circuit 13 and is driven. Further, the level setting circuit 14 generates a mute signal when the level of the input signal is lower than the level set in advance by the variable resistor 16.

Here, in addition to the usual analog display, the signal meter 15 may also display a digital display using a light emitting diode. Also, Limituta 5,
6, 7, FM detector 8, level detector 9, 10,
11, adder 12, signal meter drive circuit 1
3. The level setting circuit 14 is often implemented as an integrated circuit.

When an FM broadcast station is received, the radio wave is converted into a 10.7MHz IF (intermediate frequency) signal by the front end, the amplitude is limited by limiters 5, 6, and 7, and then output to the FM detector. Ru.
Next, when the level detectors 9, 10, and 11 detect signal levels corresponding to the IF signal levels of the limiters 5, 6, and 7, the adder 12 adds up the respective detection results, and this addition result is sent to the signal meter drive circuit. 13.

The signal meter 15 receives the drive signal from the signal meter drive circuit 13 and displays the level of the input signal.

(Problem to be solved by the invention) However, in the conventional signal meter circuit described above, when a signal higher than the level at which each limiter 5, 6, 7 operates is input, each limiter 5, 6, 7 limits the amplitude. Due to operation 7, the swing of the signal meter becomes constant. Therefore, even if an input signal higher than the amplitude-limited signal level is input, it is difficult to grasp the input signal level. In such a case, the reception state may not be such that the S/N and distortion are at their best.

That is, in FIG. 4, for example, a signal meter constructed of light emitting diodes is A,
B, C, and D are the light emitting points (operating points).

Therefore, for example, when the signal meter emits light at point D, this indicates that the level of the input signal to the antenna is at its maximum. However, as can be seen from the figure, even when the signal meter emits light at the full scale point D, the S/N does not reach the lowest value during stereo broadcast reception in section F. Become. In other words, it is unreasonable because the maximum level is displayed before the level of the signal to be input reaches the saturation point.

Here, the horizontal axis in Fig. 4 is the antenna input level,
The vertical axis shows the output level and S/N. Also,
Section F is a period from immediately before the output level E of the adder 12 reaches a saturated state to immediately after the S/N ratio during stereo broadcast reception reaches a saturated state (lowest level).

Moreover, the saturated state here means that the S/N has entered the saturated region. That is, in an FM tuner, when the level of the input signal is low, the S/N is poor, and as the level increases, noise decreases and the S/N improves. Although it differs between a stereo signal and a monaural signal, once a certain level is reached, the S/N ratio enters a region where the S/N ratio cannot be improved even if the input level is increased beyond that level.

The present invention was developed in response to such circumstances, and an object of the present invention is to provide a signal meter circuit that can appropriately indicate the level of an input signal even in the S/N saturation region.

(Means for Solving the Problem) In order to achieve the above object, the signal meter circuit of the present invention includes insertion means for selectively inserting an attenuation circuit for a predetermined period into the FM wave path of the FM tuner;
The apparatus is characterized by comprising: level detection means for detecting and holding the input level of the FM wave during the period in which the attenuation circuit is inserted; and a signal meter driven by the output of the level detection means.

(Function) In the signal meter circuit of the present invention, the insertion means is
When an attenuation circuit is selectively inserted into the FM wave path of the FM tuner for a predetermined period, the level detection means detects and holds the input level of the FM wave within that period, and the signal meter detects the input level of the FM wave by the output of the level detection means. Driven.

Therefore, since the level of the input signal is attenuated by a predetermined amount, the operating point of the signal meter can be extended to the S/N saturation region.

(Example) Hereinafter, details of an example of the present invention will be described based on the drawings. Note that parts common to those in FIG. 3 are given the same reference numerals, and redundant explanations will be omitted.

FIG. 1 shows an embodiment of the signal meter circuit of the present invention. In the figures described below, it is assumed that the signal meter performs digital display using a light emitting diode.

As shown in the figure, the signal meter circuit includes:
In addition to the conventional signal meter circuit shown in FIG. 3, the following components are added.

In other words, a tuning signal detection circuit 20 that detects a tuning signal that indicates that it is tuned to an FM station, a timer 21 that is driven by this output, a switch driver 22 that is driven by this output, and an attenuation that attenuates the level of the input signal by a predetermined amount. circuit 24, an attenuation circuit 24 between the FM antenna 1 and the front end 2;
A switch circuit 23 is provided for selectively inserting.

Then, by the output of the switch driver 22,
The attenuation circuit 24 is inserted or uninserted via the switch circuit 23.

Further, on the output side of the adder 12, there are provided a level detector 17 that detects that the output level thereof is higher than a predetermined value, and meter drivers 18 and 19 whose operation is controlled by this output.

Note that the level detector 17 is triggered by the output of the timer 21, thereby detecting the level of the input signal. Further, these meter drivers 18 and 19 are connected to the tuning signal detection circuit 2.
The operating state is also reset by the out-of-tuning detection output from 0.

On the output sides of the meter drivers 18 and 19, signal meters 15A and 15B are provided that perform light emission display based on these outputs.

The signal meter circuit having such a configuration operates as follows.

First, the switch circuit 23 normally has an attenuation circuit 24.
The contact position is switched to non-insertion.

When the tuning signal detection circuit 20 detects that the tuning signal is tuned to the FM station, the timer 21 is driven. Here, the tuning signal is, for example, an automatic stop signal in the case of a synthesizer tuner.

When the timer 21 is activated, the switch driver 22 is activated, thereby switching the switch circuit 23 to the contact position where the attenuation circuit 24 is inserted.
Here, the time during which the switch circuit 23 is switched to that position is within the time during which the timer 21 is to be driven, and this time is predetermined.

As a result, the attenuation circuit 24 is inserted between the FM antenna 1 and the front end 2, and the output of the FM antenna 1 is attenuated and supplied to the front end 2.

On the other hand, the level detector 17 is triggered by the occurrence of the output of the timer 21, which causes the adder 1
Detect the output of 2.

At this time, if the output of the adder 12 exceeds a predetermined level, the meter drivers 18 and 19 are controlled to be in an operating state, and the operating state is held. Further, when the output of the adder 12 is below a predetermined level, the meter drivers 18 and 19 are rendered inactive.

Then, when the tuning signal disappears due to the next tuning operation, etc., the output of the tuning signal detection circuit 20 disappears and the meter driver 18, 19 becomes out of tune.
will be reset. Further, when the timer 21 has elapsed for a predetermined period of time, the switch circuit 23 uses a drive signal from the switch driver 22 to cause the attenuation circuit 24 to
is switched to a state where it is removed from between the FM antenna 1 and the front end 2.

Here, when the attenuation circuit 24 is inserted between the FM antenna 1 and the front end 2, the output of the FM antenna 1 is supplied to the front end 2 after being attenuated by the attenuation circuit 24. This is equivalent to moving the horizontal axis of the output characteristic of the adder 12 to the right as shown in FIG.

That is, as shown in FIG. 2, the output of the adder 12 normally saturates at an input level of 25 dBf. During this period up to saturation, the signal meter 15
performs the light emitting operation in the order of A, B, C, and D.

Here, for example, set the light emission level at point D to 20dBf.
It is assumed that the attenuation amount of the attenuation circuit 24 is 20 dBf.

At this time, the level of the input signal obtained through the antenna 1 is attenuated by 20 dBf by the attenuation circuit 24, so the horizontal axis moves by 20 dB to the (+) side with respect to point D. This results in
25, 35, 45, 55 when the attenuation circuit 24 is not inserted
Since dBf corresponds to 5, 15, 25, 35...dBf after insertion, the output of the adder 12 appears to be as shown by the broken line with respect to the input.

As a result, the output of the adder 12 is equivalent to having its non-saturation level expanded by 20 dB.

Therefore, by appropriately setting the amount of attenuation of the attenuation circuit 24, the signal meters 15A and 15B perform a light emitting operation in response to the input in the range of section F in FIG. 4, so that the maximum tuning point can be displayed. I can do it.

As a result, it is possible to appropriately indicate the level of the input signal even in the S/N saturation region.

Note that the timing for inserting the attenuation circuit 24 described above is better audibly when the output of the adder 12 rises sufficiently relative to the input and after the signal meter drive circuit 13 and signal meter 15 have finished their operations. It feels less unnatural. Furthermore, when the attenuation circuit 24 is inserted, the signal meter 15 may turn off, so the signal meter drive circuit 13
It is desirable to also have a hold function. Furthermore, during the sequence of insertion and non-insertion of the attenuation circuit 24, it is desirable to apply muting because large fluctuations are given to the audio signal.

In this way, in this embodiment, the apparent level of the input signal is attenuated by a predetermined amount so that the operating point of the signal meter extends to the S/N saturation region. It becomes possible to appropriately indicate the signal level.

As a result, it is possible to know whether the strength of the radio waves from the FM station is sufficient for the performance of the device, or the absolute value of the input strength, etc., regardless of the saturation characteristics of the signal meter circuit.

In this embodiment, the case where the insertion position of the attenuation circuit 24 is between the FM antenna 1 and the front end 2 has been explained, but this is not limited to this example, and it can be inserted between the FM antenna 1 and the limiter 7. Similar effects can be obtained at any position.

In addition, the switch circuit 23 does not need to be connected to both the input side and the output side of the attenuation circuit 24; it can be connected only to either the input side or the output side, or the signal line can be terminated if it does not interfere with normal operation. It may be in the form of

Furthermore, in this embodiment, a case has been described in which the level detector 17 is provided independently, but it is not limited to this example, and it may be combined with the signal meter drive circuit 13, and in this case, the circuit configuration is simple. be converted into

Furthermore, in this embodiment, the meter driver 1
I explained the case where two 8 and 19 were provided, but
The number is not limited to this example, and the number may be three or more as necessary. In this case, it is necessary to make the number of signal meters correspond to the number of each meter driver. An example of this case is shown in FIG.

Further, the hold function of each meter driver 18, 19 may be provided in the level detector 17.

Furthermore, in this embodiment, the attenuation circuit 24
Although we have explained the case where one is provided, the attenuation circuit 24 is not limited to this example, and can be made to correspond to all input levels by using multi-stage attenuation circuits, and by adding and displaying indicators according to each stage, the signal input level can be adjusted. It is also possible to display a display with good linearity.

Further, in this embodiment, a case has been described in which a tuning signal is supplied to the tuning signal detection circuit 20, but the present invention is not limited to this example, and instead of the tuning signal, a separate signal may be supplied at regular time intervals. This case is suitable, for example, when rotating the FM antenna 1 to search for a good position in the antenna direction.

(Effects of the invention) As explained above, according to the signal meter of the invention, the level of the input signal is attenuated by a predetermined amount,
Since the signal meter's operating point extends to the S/N saturation region, it is possible to appropriately indicate the level of the input signal even in the S/N saturation region. be able to appropriately indicate the level of

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the signal meter circuit of the present invention, Fig. 2 is a characteristic diagram for explaining its operation, and Fig. 3 is a block diagram showing an example of a conventional signal meter circuit. FIG. 4 is a characteristic diagram for explaining the operation. 1...FM antenna, 2...front end,
3, 4... Ceramic filter, 5, 6, 7...
...limiter, 8...FM detector, 9, 10, 11
...Level detector, 12...Adder, 13...Signal meter drive circuit, 15, 15A, 15B...
...Signal meter, 17...Level detector, 1
8, 19...meter driver, 20...tuned signal detection circuit, 21...timer, 23...switch circuit, 24...attenuation circuit.

Claims (1)

[Scope of utility model registration request] insertion means for selectively inserting an attenuation circuit into the FM wave path of the FM tuner for a predetermined period; level detection means for detecting and holding the input level of the FM wave during the period in which the attenuation circuit is inserted; A signal meter circuit comprising: a signal meter driven by the output of the level detection means.