JPS60146531A - Receiver - Google Patents

Abstract

PURPOSE:To receive an FM signal with excellent selectivity by detecting a frequency or an amplitude of a beat output from a phase comparator so as to switch the connection to a speaker when a carrier of a PLL at the outside of locking range is received. CONSTITUTION:An FM signal from a main line 23 is received by a PLL comprising a phase comparator 19, an LPF20 and a voltage controlled oscillator VCO21. A beat output generated at the outside of locking range of the PLL is detected (25), amplified (26) and rectified (27) so as to control an analog switch 28. When the signal of a channel other than the own station is received, the switch 28 is turned off so as not to drive (7) a speaker 6. Thus, the FM signal is received with an excellent selectivity. This system is suited for the constitution of the in-home information network.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a receiving device that demodulates a frequency modulated (FM) signal with a simple method and good selectivity.

Background: With the advancement of the information society, home security systems with sensor networks for crime prevention and disaster prevention, as well as home/mu telephones with functions such as intercoms, door phones, and parent/child telephones, have come into practical use. It is expected that it will further develop as a so-called home information and communication network.

Home appliances that have traditionally been used in homes have become intelligent by incorporating microcomputers, etc., and have been incorporated into home information and communication networks along with new media devices such as CATV, teletext, and captains. The idea is to save energy and labor by centrally monitoring and controlling all devices using a home computer.

In this way, a home information communication network must handle various signals such as control signals, audio signals, and video signals, and it is easy to expand and change the system, is highly productive and economical, and has a good appearance. It must be designed to avoid damage.

Currently, transmission media in homes include wireless media such as weak radio waves and infrared rays, and wired media such as coaxial cables, twisted pair wires, and optical fiber cables. It is unrealistic in terms of scalability and appearance to string lines all over the place, and when using wireless media sound, multiplex transmission technology is essential, as is the case in the past. Possible multiplex transmission technologies include 1) frequency division multiplexing, II) time division multiplexing, and 1+: code division multiplexing, but ++) and *:1) require that all signals be digitized, and currently However, it is unsuitable for home use from the point of view of economy, and the frequency division multiplexing method (1) is considered to be the most suitable for practical use.

Now, many of the intercoms that have been used in the past have a system in which the number of wires connected to the intercoms is as many as the number of intercoms to be connected, and the user uses a switch to select the wire for the room he or she wants to call. However, this method of drawing lines for the number of connected intercoms allows baseband transmission, so there is no need for each intercom to have a modulation/demodulation circuit, which has the advantage of simplifying the circuit configuration. Not only does changing or expanding the system require new wiring work, but it is also extremely inflexible from the perspective of constructing a home information communication network.

On the other hand, in order to multiplex transmit audio signals, K must modulate high-pitched signals, but this method must be easy and suitable for home use, and must not yield the desired performance. No. In this case, as a modulation method, there are drawbacks such as a wide occupied band and a slightly complicated modulation/demodulation circuit, but it is resistant to noise and interference, and the volume after demodulation does not depend on the input signal level, so the automatic gain control circuit (AGC circuit It has many advantages such as no need for S), and the modulation signal amplification circuit is class 6 and highly efficient.
Frequency modulation is considered to be the most suitable method.

Here, it should be noted that the modulation/demodulation circuit must be able to receive the signal of the desired channel with good selectivity since the audio signals of multiple channels are widely transmitted by frequency division multiplexing.

By the way, demodulation methods for frequency modulated (FM) signals include Foster-Sheeley type and ratio detection type.

There are many different types, such as quadrature detection type and pulse count type, and each type uses an IC circuit, and each has its own advantages and disadvantages.

On the other hand, the FM method has the effect of improving the signal-to-noise power ratio (SN ratio) compared to the amplitude modulation (AM) method if the input signal is above a certain level. Below this level, there is a so-called Threnholt phenomenon in which the SN ratio becomes worse than that of the AM method, and this level is called the threshold level. There are various techniques for improving the Threnhold phenomenon, that is, lowering the Threnhold level, one of which is the phase-locked loop (PLL).
) has recently been converted into an IC, making it easier to handle.

Figure 4 shows a system diagram of a PLL type FM demodulator, where 19 is a phase comparator, 20 is a loop filter, 2
1 represents each voltage controlled oscillator (VCO). The phase difference between the input FM wave and the output of the VCO is determined by the phase comparator 1.
The output signal φ is detected by a loop filter 20 to remove out-of-band noise, and then fed back to the VCO 21 in a negative manner. To control the frequency of vCO21, VCO2
The oscillation frequency of 1 is synchronized with the frequency of the inlet FM wave, that is, V
The control voltage of 6O13 becomes the demodulated output as shown in the figure. Furthermore, the PLL has the property that it synchronizes to input signals within a certain band centered on all free-running frequencies of the VCO 21, but does not synchronize to input signals outside of that band. range or capture
In other words, for slight fluctuations in the transmission carrier due to the compression characteristics of the modulation circuit, P L
Demodulation is possible due to the function of L as a tracking filter. Therefore, by ensuring that the frequency difference between the transmit carriers between channels is greater than the capture range, there will be no false synchronization with the input signal of other channels, and since the PLL itself has tuning capability, there is no need to add an external filter for tuning. None. In addition, an amplitude limiting circuit (limiter) is usually essential for FM demodulators, but in the case of the PLL system, the amplitude changes of the input signal are compressed by the internal negative feedback ring, so 0.
! It has almost no effect on the modulation output and does not require a limiter.

In this way, in order to stabilize the single-sphere transmission carrier more than necessary, a simple modulation circuit can be used without using expensive parts such as a crystal oscillator. Yes, there is no need to add an external channel selection filter.
l11) No limiter required in the input section, I■) Low cost as there are many monolink IC types available, V) PLL
The VCO, which is a component of the FM modulation circuit,
It is extremely appropriate to fully adopt the PLL system as a simple system suitable for home use, since it can be simplified by sharing the modulation/demodulation circuit.

Figure 5 shows the intercom circuit used in the PLJ. 22 is a time constant circuit that determines the free-running frequency of the VCO2, which is usually a resistor or capacitor or both, and 23 is a time constant circuit that determines the free-running frequency of the VCO2. Each represents a trunk cable. Each intercom usually has the free-running frequency of the VCO2+ matched to the frequency of the channel assigned to its own station, and when making a call, by matching the transmitting frequency of the own station, that is, the free-running frequency of the VCO2+ to the channel of the other party you want to talk to. You can now make calls. In addition, 6 is a speaker, 7 is its Masakabata device, 8 is a microphone, and 9 is its amplifier.

Reference numeral 10 is a transmitting switch (pre-storage), and reference numeral 11 is a switch for selecting all call parties.

I mentioned earlier that PLL does not synchronize with input signals outside the capture range, but since the input signal is FM modulated with an audio signal, it will synchronize as the input signal changes in frequency.
If the oscillation frequency of the VCO 21 repeatedly approaches and moves away from the frequency of the human input signal and is not synchronized, the baseband component may drop in the demodulated output, that is, the control voltage of the VCO 21. , good selectivity cannot be obtained. The present invention solves this problem based on the operating principle of PLL. That is, when input signals with different frequencies are applied, the phase comparator 19 performs all operations as a mixer due to its non-linear operation, and outputs a beat signal corresponding to the frequency difference between the two signals as an output signal of the VCO2+ as an all-local oscillation signal. is generated and the input signal has a frequency outside the capture range, the VC
The oscillation frequency of O2+ is controlled by this beat output, and it only repeats approaching and departing from the input signal frequency, but is never synchronized forever, and the beat output is also at its maximum amplitude.0 Figure 6 shows the total beat output. l'l with spectrum analyzer
(This shows an example where +1 is constant. In this example, ( is VCO2
The free-running frequency of 1 is set to ]MHz, the capture range of PLL is set to ±60 kl (z, and the same figure (a)
) is when the input signal frequency is IMHz, (b') is when the input signal frequency is 0.8MHz, (c) is when the input signal frequency is ], and (d) is when the input signal frequency is 2 MHz.
It is a universal measurement type when the input signal frequency is 4 MHz. Center of horizontal axis Fi IMHz, l scale 200
In kHz, one division on the vertical axis is 10 dB. Figure 7 also shows an example observed with a synchroscope.
In this example, the free running frequency of VCO21 is 2MHz%
The capture range of the PLL is set to ±60kHz, and the input signal frequency in the figure <a) is ], 2 MH
In the case of z, the figure (b) is an observation example when the input signal frequency is IMHz, and the figure (c) is an observation example when the input signal frequency is 1.4MHz.

One division on the horizontal axis is 2 μsec, and one division on the vertical axis is 2V. It can be seen that both (b) and (c) of the same figure are in a state where they are not synchronized with the input signal, and the beat output is saturated, that is, has a long and large amplitude.

<Object of the Invention> In view of the above points, the present invention provides a technique for receiving frequency modulated signals transmitted by frequency division multiplexing with a simple circuit configuration suitable for home use and with good selectivity. According to the present invention, it is possible to construct a home information communication network that is highly expandable, economical, and convenient.

<Example> Hereinafter, with reference to FIGS. 1 to 3, a detailed explanation will be given of an example of the present invention.

FIG. 3 shows a system configuration diagram of the home information communication network that is the object of the present invention. 12 is a television antenna, 13 is a public line network, 14 is a network termination device, 15 is, for example, a coaxial cable, 16, 16 .
... is an interface unit, I7. I7. ...
18 represents network connection devices or terminal devices such as sensors, actuators, home appliances, telephones, and intercoms, and 18 represents all home computers that centrally monitor and control them.

The intercom is constructed as shown in FIG. In the figure, a beat frequency detection filter 25. Beat amplification circuit 26. Rectifier circuit 27° analog switch 2
8 have been newly added.

Further, 24 is a low-pass filter for the audio band.

Here, when the PLL is not synchronized, that is, when receiving a signal from another channel, the beat output is detected by the filter 25 that detects all beat frequencies, is amplified by the beat amplification circuit 26, and is amplified by the rectifier circuit 27. By rectifying and controlling the analog switch 28, if a signal other than the own channel is being received, the analog switch 'c
OFF I/C to prevent the speaker from operating.

FIG. 2 is for explaining another configuration example of the interphone according to the present invention, which takes advantage of the fact that the beat output is at its maximum amplitude when the PLL is not synchronized with the input signal. , 29 is a comparator for detecting the maximum amplitude, 30 is a voltage source with an open threshold, and 31 is a monostable multi-by-break.
If the input to the comparator 29 exceeds the threshold level in the beat period, the comparator output is converted to DC by the monostable multivibrator 31, and the analog switch 28
f: Controlling.

Although the intercom has been described above as an application example of the present invention, it goes without saying that the present invention can also be applied to transceivers, telemeters, and many other uses.

<Effects of the Invention> The present invention receives frequency-modulated signals with good selectivity, can be realized in an extremely easy method, and can be particularly effectively applied in constructing a home information communication network. The present invention has a wide range of applications and is very effective.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG.
The figure is a block diagram showing another embodiment of the present invention. Figure 3 is a system configuration diagram of a home information communication network to which the present invention is applied. Figure 4 is a basic block diagram of a viPLL type FM demodulator. , Fig. 5 is a basic block diagram of the FM intercom used in PLL', and Fig. 6(a) to (
d) Diagram of beat output measurement during asynchronous time using U spectrum analyzer. FIGS. 7(a) to (C) are diagrams of measurement using the same synchroscope. 06 Speaker, 7...Amplifier, 8...Microphone. 9°゛Amplifier, 10... Transmission switch, 11... Call party selection switch, 19... Phase comparator, 20... Low pass filter, 21... Voltage controlled oscillator, 23...
Time constant circuit, 24...Audio bandpass filter, 25°
. Beat frequency detection filter, 26... amplifier, 27.
・Rectifier circuit, 28...Analog switch, 29...Comparator, 30-゛°voltage source, 31°゛Monostable-Multivibrator 0 Agent Patent attorney Yoshihiko Fuku (and 2 others) 3r
A 5 1 ・1 ・ 4 i, (Stirrup 1 (= 5 Figure 51F 51) ME 5PAN2.OMHl C;F
1. uu Mnt(b) (d) Figure 6

Claims (1)

[Claims] 1 The frequency modulated signal is passed through a phase-locked loop (PLL
)? : means for detecting the frequency and/or amplitude of the beat output from the phase comparator when receiving an input signal with a carrier frequency outside the locking range of the phase-locked loop, in a receiver that demodulates using and switching means for turning on and off an electric path to a speaker based on the detection output.