JPH054863B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention combines two detection methods.
Regarding FM receiver.

[Prior Art] There are various detection methods in an FM receiver, such as a pulse count method, a PLL method, and a PTL method. Conventional FM receivers have been configured to adopt one of the above-mentioned detection methods in consideration of various circumstances such as usage conditions.

[Problem to be solved by the invention] However, since each detection method has its advantages and disadvantages, adopting only one detection method will inevitably result in not being able to obtain the advantages that only other detection methods have. It turns out.

Specifically, the PLL method has the following advantages.

Wide detection range, no dependence on tuning circuit, and stable characteristics.

Since it demodulates mainly the necessary signals, it has the ability to eliminate interference.

Because it has AM suppression ability, it can provide better reception than other detection methods when the received signal is weak.

However, in this PLL system, it is difficult to improve distortion and S/N ratio due to the characteristics of the elements (eg, varicap) used in the voltage controlled oscillator (VCO).

On the other hand, the pulse count method has the following advantages.

It has such wide linearity that it is called a linear detector.

Characteristics are extremely stable as there is no tuning circuit.

It is possible to use the double conversion method in combination, and a high S/N can be obtained.

This invention was made in consideration of such circumstances, and includes a pulse count type detection section,
When the received signal level is strong, it utilizes the advantages of the pulse count method to receive signals with good distortion and S/N ratio.
In addition, when the received signal level is weak, by taking advantage of the PLL method and receiving with high sensitivity, it is possible to obtain good FM over a wide range of received signal strengths and weaknesses.
The purpose is to provide a receiver.

[Means for Solving the Problems] The FM receiver of the present invention includes: a front end that selects and tunes an FM reception signal received from an antenna, converts it into an intermediate frequency signal, and outputs it; and a front end that outputs the intermediate frequency signal. an intermediate frequency amplification section that amplifies; and a first detection unit of a pulse count method that converts the intermediate frequency signal amplified by the intermediate frequency amplification section into a compression wave of pulses with a constant width, and then obtains a detection output through an integrating circuit. and a PLL method that automatically controls a voltage controlled oscillator in a closed loop so that it oscillates in phase and frequency matching with the intermediate frequency signal amplified by the intermediate frequency amplification section, and obtains a detection output from the control signal. a second detection unit; a stereo demodulation unit that inputs the detection output and separates it into left and right signals; and a switching unit that selectively inputs the detection outputs of the first and second detection units to the stereo demodulation unit. a signal level detection unit that detects the signal level of the intermediate frequency signal; and inputting the detection output of the first detection unit to the stereo demodulation unit when the signal level of the intermediate frequency signal exceeds a predetermined value. , and a switching control section that controls the switching means so as to input the detection output of the second detection section to the stereo demodulation section when the signal level of the intermediate frequency signal is below a predetermined value; and the left and right signals. and a low frequency amplification section that amplifies and outputs the amplified signal to a speaker.

[Function] The FM receiver of the present invention combines a pulse count type detection unit and a PLL type detection unit,
When the received signal level is high, a pulse count type detection section is used, and when the received signal level is low, it is used.
By using a PLL type detection section, high S/N can be achieved over a wide range regardless of the strength of the received signal.
Realize the ratio.

[Example] Hereinafter, an example of the present invention will be described based on the drawings. The FM receiver of this embodiment is configured to also function as a television audio multiplex receiver.

First, the mechanical part of the FM receiver will be explained.

In Fig. 1, 1 is an FM front end, 2 is an intermediate frequency amplification section, 3 is a pulse count detection section, 4 is a PLL detection section, 5 is a stereo demodulation section, and 6 is a low frequency amplification section. is the basic component. The pulse count type detection unit 3 and the PLL type detection unit 4 are connected in parallel, and their detection outputs are selectively input to the FM stereo demodulation unit 5 by the switching means 7. There is.

The front end 1 has a general configuration, and selects and tunes the signal to be received from the FM reception signal received by the antenna, converts it into an intermediate frequency signal, and outputs the signal. Normally, this front end 1
consists of three circuits: a high-frequency amplification section, a mixer section, and a local oscillation section.

The intermediate frequency amplification section 2 also has a general configuration, with a plurality of filters and amplifiers connected in multiple stages, and amplifies the intermediate frequency signal from the front end 1. This intermediate frequency amplification section 2 may be equipped with a narrowband bandpass filter,
In that case, when there is an adjacent interference signal, a narrowband bandpass filter is automatically or manually switched and connected in the amplifier circuit to narrow the bandwidth.

The pulse counting type detection section (hereinafter referred to as "first detection section") 3 also has a general configuration of the same type. In other words, the intermediate frequency signal amplified by the intermediate frequency amplification section 2 is converted into a compressional wave of pulses with a constant width, and then the detection output is obtained through an integrating circuit. Basically, a limiter amplifier and a differential It consists of a circuit (trigger circuit), a monostable multivibrator, and an integrator.

The PLL type detection section (hereinafter referred to as "second detection section") 4 basically has a general configuration of the same type. That is, as shown in FIG. 2, a phase comparator 4a and a low-pass filter (hereinafter referred to as
It is composed of a voltage controlled oscillator (hereinafter referred to as "VCO") 4c, and oscillates in phase and frequency with the intermediate frequency signal amplified by the intermediate frequency amplification section 2. As you do,
The VCO4c is automatically controlled in a closed loop, and the detected output is obtained from the control signal. Furthermore, in the case of this detection section 4, the time constant of the low-pass filter 4b can be changed in two steps by the field effect transistor FET1.
That is, when FET1 is turned on, capacitors C1 and C2 are connected in parallel, and the cutoff frequency is kept low. In this example, the cutoff frequency is kept low enough to provide monaural sound.

The stereo demodulation section 5 has the same configuration as a general one, and separates the detection output selectively inputted from the first detection section 3 or the second detection section 4 into left and right signals through the switching means 7. . Further, the low frequency amplification section 6 is a general type, and amplifies the left and right signals from the stereo demodulation section 5, and outputs the amplified signals to a speaker (not shown). This low frequency amplification section 6 is equipped with a high blend function section 6a that mixes left and right signals to remove noise when the electric field is weak.

Reference numeral 8 denotes a cutoff frequency control section (hereinafter referred to as "first control section") that controls the FET in the LPF 4b of the PLL detection section 4 described above. 9 is
This is a switching control section (hereinafter referred to as "second control section") that controls the switching means 7 described above. 10 is
This is a high blend control section (hereinafter referred to as "third control section") that controls the high blend section 6a described above. These first, second, and third control units 8, 9,
10 inputs the detection signal of the signal level detection section 11 and performs a predetermined control function according to the signal level. The signal level detection section 11 detects the signal level in the intermediate frequency amplification section 2 described above. The functions of the control units 8, 9, and 10 will be described later along with their actions.

Next, the components of the television audio multiplex receiver will be explained.

The reception system of this embodiment is a separate carrier system, and the video intermediate frequency signal from the front end 21 is selected by a filter and input to the video intermediate frequency amplification section 22. The video intermediate frequency signal is amplified by the video intermediate frequency amplification section 22, detected by the video detection section 23, and detected by the video amplification section 2.
4 and is amplified and displayed on the screen. On the other hand, the audio signal selected from the front end 21 by the filter is converted into an intermediate frequency signal by the TV audio intermediate frequency converter 25. This intermediate frequency signal is input to the switching means 26 together with the intermediate frequency signal from the FM front end 1 described above, and is selectively inputted by the switching means 16 to the intermediate frequency amplifying section 2 described above. Also, in Figure 1, 27
is a general TV audio multiplex demodulator, which separates the detection output input through the switching means 7 into left and right signals. The left and right signals are inputted to the switching means 28 together with the left and right signals from the FM stereo demodulation section 5 mentioned above, and are selectively inputted to the low frequency amplification section 6 mentioned above by the switching means 28.

Further, 29 is a dual mode detection section. Dual mode means that the main channel (Japanese broadcast) and sub channel (foreign language broadcast) can be output separately from the left and right speakers, or only the main channel or sub channel can be output from the left and right speakers. This is a usage mode in which output is output from a speaker, and is selected by operating a changeover switch. Therefore, the dual mode detection section 24 can detect that the dual mode has been selected from the operating state of the changeover switch.

Further, 30 is an FM/TV switching control section, which outputs a switching control signal to the aforementioned switching means 26 and 28 depending on the reception status of FM broadcast or TV broadcast. The reception status of FM broadcasting and TV broadcasting is detected, for example, from the switching state of a switch for receiving broadcasting.

Next, the function as an FM receiver will be explained (see Fig. 3). While receiving FM broadcasts, FM/
The TV switching control section 30 switches the switching means 26 and 28 to the first
The switching state is as shown in the figure.

First, when the signal level detected by the signal level detection section 9 exceeds the level L1, the second control section 9 sets the switching means 7 to the switching state as shown in FIG. The detected output is input to the stereo demodulator 5. Therefore, at this time, it operates as an FM receiver equipped with a pulse count type detection section. As is clear from FIG. 3, the level L1 is a level below which the S/N ratio of detection using the pulse count method begins to decrease, and is, for example, 40 dBf.

When the signal level becomes equal to or lower than level L1, the second control section 9 switches the switching means 7 to the second detection section 4 side, and inputs the detection output of the detection section 4 to the stereo demodulation section 5. Therefore, at this time,
Operates as an FM receiver equipped with a PLL detection section. Also, at this time, the first control section 8
1 in the OFF state, in the PLL detection section 4.
The cutoff frequency of LPF4b is set relatively high. In the case of such PLL type detection, as is clear from FIG. 3, a high S/N ratio is maintained even if the S/N ratio of pulse count type detection is lower than level L1.

When the signal level becomes lower than the level L2, the first control section 8 turns on the FET 1, suppresses the cutoff frequency of the LPF 4b in the PLL detection section 4 to a low level, and makes it a monaural state.
This will suppress a decrease in the S/N ratio. Note that the level L2 is, for example, 18 dBf.

Furthermore, when the signal level falls below a predetermined set value and it becomes necessary to remove noise, the high blend function section 6a operates. The set value is set in advance by the third control unit 10, and when the signal level falls below the set value, the third control unit 10 automatically activates the high blend function unit 6a. .

As described above, the detection method can be changed, the high blend function can be controlled,
By changing the cutoff frequency of the LPF 4b in the PLL detector 4, a high S/N ratio can be obtained over a wide range of signal levels, as shown in FIG.

Next, the function as a TV audio multiplex receiver will be explained. When receiving TV broadcasts, FM/
The TV switching control section 30 switches the switching means 26 and 28 to the first
Switch upward from the state shown in the figure.

First, the front end 21 is
The audio intermediate frequency signal selected from the above passes through the TV audio intermediate frequency converter 25, and is subjected to intermediate frequency amplification, demodulation, and low frequency amplification as in the case of the FM reception signal described above, and is output to the speaker. Naturally, in this case, the main channel audio signal and the sub-channel audio signal will be demodulated separately.
If you are currently receiving bilingual broadcasts, you can listen to them using the main mode where you listen to Japanese broadcasts from the left and right speakers, the sub mode where you listen to foreign language broadcasts from the left and right speakers, and the dual mode mentioned above. There is. That is, the dual mode is a usage mode in which Japanese broadcasts and foreign language broadcasts are output separately from the left and right speakers, or only the main channel or only the subchannel is output from the left and right speakers. The dual mode is indicated by the dual mode detection unit 24.
The third
The control unit 10 automatically disables the high blend function unit 6a. Therefore, in the dual mode, the high blend function section 6a does not work regardless of the signal level. As a result, the problem that occurs when bilingual broadcasts are blended in the dual mode, that is, the bilingual broadcasts are mixed and becomes difficult to hear, can be avoided.

[Effects] As explained above, the FM receiver of the present invention combines a pulse count type detection unit and a PLL type detection unit, and uses the pulse count type detection unit when the received signal level is high. Since the configuration uses a PLL detection section to perform detection when the received signal level is low, a high S/N ratio can be achieved over a wide range regardless of the strength of the received signal.

[Brief explanation of the drawing]

The drawings are diagrams for explaining one embodiment of the present invention, and FIG. 1 is a block diagram, and FIG. 2 is a block diagram.
FIG. 3 is a block diagram of the PLL detection section, and is a diagram for explaining the operation. DESCRIPTION OF SYMBOLS 1...Front end, 2...Intermediate frequency amplification section, 3...Pulse count detection section (first detection section), 4...PLL detection section (second detection section), 5...
...Stereo demodulation section, 6...Low frequency amplification section, 7...
Switching means, 9... switching control section (second control section),
11...Signal level detection section.

Claims (1)

[Claims] 1. Tuning the FM reception signal received from the antenna,
a front end that tunes the signal, converts it into an intermediate frequency signal, and outputs it; an intermediate frequency amplification section that amplifies the intermediate frequency signal; and an intermediate frequency signal amplified by the intermediate frequency amplification section that converts the intermediate frequency signal into a compression wave of constant width pulses. After converting to
A first detection section of a pulse counting method which obtains a detection output through an integrating circuit, and a voltage controlled oscillator in a closed loop so that it oscillates in phase and frequency matching with the intermediate frequency signal amplified by the intermediate frequency amplification section. a PLL type second detection section that automatically controls and obtains a detection output from the control signal; a stereo demodulation section that inputs the detection output and separates it into left and right signals; and the first and second detection sections. switching means for selectively inputting the detection output to the stereo demodulation section; a signal level detection section for detecting the signal level of the intermediate frequency signal; The detection output of the first detection section is input to the stereo demodulation section, and the detection output of the second detection section is input to the stereo demodulation section when the signal level of the intermediate frequency signal is below a predetermined value. , comprising: a switching control section that controls the switching means; and a low frequency amplification section that amplifies the left and right signals and outputs the amplified signals to a speaker.
FM receiver.