JPH03106147A - Phase locked loop oscillator - Google Patents

Abstract

PURPOSE:To improve the communication quality between stations by providing a voltage control means to an input of a voltage controlled oscillator so as to avoid disabled clock extraction by each station thereby preventing disabled communication between stations. CONSTITUTION:When a frequency of a reference clock signal is largely fluctuated and a signal (a) is inputted from a low pass filter 11, A voltage limit circuit 15 limits a voltage and outputs a signal (b) to a voltage controlled oscillator 12. As a result, the frequency fluctuation of the voltage controlled oscillator 12 is suppressed. That is, even when the reference clock signal (output clock from a private branch of exchange) is subjected to faulty frequency, the frequency fluctuation of the output clock of a phase locked loop oscillator of a master station is suppressed small and disabled clock extraction by each station is avoided. Thus, the communication quality between stations is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial field) The present invention relates to a phase synchronized oscillator used in a local area network (LAN) or the like.

(Prior Art) In a loop network system as a type of local area network, a plurality of stations are connected in a loop via transmission paths, and communication is performed between each station.

FIG. 3 is a diagram showing the configuration of such a loop network system, in which a master station 1 and multiple stations 2-1 to 2-n
are connected in a loop by a transmission line 3. When communicating between multiple stations 2-1 to 2-n, the master station 1 generates the clock signal, and the other stations 2-1 to 2-n extract the clock signal from the bit string in the loop. Based on this, the logic circuit within the station operates.

Further, as shown in the figure, such a loop network system may be connected to a wide area network 5 via a private branch exchange (PBX) 4. In such a case, the master station 1 generates a clock signal using the phase synchronized oscillation shown in FIG. 2 based on the reference clock signal sent from the wide area network 5.

This conventional phase-directed oscillator compares the phase of the reference clock signal (output clock of the local exchange machine) and the output signal from the frequency divider 13, and sends a signal according to the phase difference to the low-pass filter 11. a low-pass filter 11 that outputs only a signal with a predetermined low frequency, and a voltage-controlled oscillator 12 that oscillates a pulse signal according to the signal sent from the low-pass filter 11 and sends it to an output terminal and a frequency divider 13. and a frequency divider 13 that divides the frequency of the pulse signal output from the voltage controlled oscillator 12 and sends it to the phase comparator 10.

However, in this case, if the reference clock signal (output clock) of the private branch exchange 4 is not synchronized with the wide area network 4,
A clock with a normal frequency is supplied to master station 1, and the output frequency of the phase synchronized oscillator of master station 1 also becomes abnormal, exceeding the frequency range in which each station's clock can be extracted, making communication between each station impossible. There was a case.

(Problems to be Solved by the Invention) As described above, in the conventional loop communication system, there is a problem in that when the output clock frequency of the private branch exchange greatly fluctuates, it becomes impossible to extract the clock of each station.

The present invention was made in order to solve the above-mentioned problems, and even if the output clock frequency of the private branch exchange varies greatly, the frequency variation of the clock generated by the master station is small, and communication between each station is maintained. The purpose of this invention is to provide a phase-locked oscillator.

[Structure of the Invention (Means for Solving the Problems) The present invention achieves the above-mentioned conventional objects by connecting a plurality of stations in a loop through a transmission path, and a master station generates a clock synchronized with a network clock. Each station extracts a clock from the received signal, and in the phase synchronized oscillator that generates the clock and is installed in the master station of the time division multiplex loop communication system in which each station communicates, the human power side of the voltage controlled oscillator is The present invention is characterized in that a voltage limiting means is provided to prevent each station from extracting a clock, thereby preventing communication between the stations.

(Function) In the present invention, even if the output clock frequency of the private branch exchange greatly fluctuates, the input voltage of the voltage controlled oscillator does not fluctuate more than a certain level, so that fluctuations in the frequency of the clock generated by the master station are prevented.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing the structure of a phase-locked oscillator according to an embodiment of the present invention.

The phase synchronized oscillator of the embodiment shown in the figure has a phase comparator 10.
, a low-pass filter 11, a voltage limiting circuit 15, a voltage controlled oscillation W12, and a frequency divider 13.

The phase comparator 10 compares the phase of the standard clock f=signal St (private branch exchange output clock) input from the input terminal 21 with the output signal from the frequency divider 13, and lowers the signal according to the phase difference. It is sent to the bandpass filter 11. The low-pass filter 11 is
Only signals of a predetermined low frequency are sent to the voltage limiting circuit 15. Voltage limiting circuit 15 supplies the signal sent from low-pass filter 11 to voltage 1:restricted oscillator 12 . in this case,
The frequency of the reference clock signal fluctuates greatly, as shown in Fig. 4 (a).
) is input from the low-pass filter 11, the voltage limiting circuit 15 limits the voltage and outputs a signal as shown in FIG. 4(b) to the voltage controlled oscillator 12. As a result, the frequency fluctuation of the voltage controlled oscillator 12 is suppressed as shown in FIG. 4(c).

Voltage controlled oscillator 12 sends a pulse signal to output terminal 22 and frequency divider 13 . The frequency divider 13 is a voltage controlled oscillator 12
The output pulse signal is frequency-divided and sent to the phase comparator 10.

As a result, in this embodiment, even if the reference clock signal (output clock of the private branch exchange) becomes an abnormal frequency, the frequency fluctuation of the output clock of the phase synchronized oscillator of the master station is suppressed to a small level, so that the clock extraction of each station is Communication quality between stations can be greatly improved.

[Effects of the Invention] As explained above, according to the present invention, even if the over-standard clock signal becomes an abnormal frequency, the output frequency deviation of the master station can be suppressed to a small level, making it impossible to extract the clock of each station. Things will disappear.

As a result of this, the quality of communication between stations is greatly improved.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a phase-locked oscillator according to an embodiment of the present invention, FIG. 2 is a block diagram showing a 4++7 configuration of a conventional f-th synchronous oscillator, and FIG. 3 is a block diagram showing a 4++7 configuration of a conventional f-th synchronous oscillator. Schematic configuration diagram, Figure 4 (a) to (c)
2 is an explanatory diagram of the operation of the voltage limiting circuit shown in FIG. 1. FIG. 1... Master station, 2-1 to 2-n... Station, 3...
Transmission line, 4...Private branch exchange, 5...Wide area network, 10.
... Phase comparator, ]1 ... Low-pass filter, 12 ...
Voltage controlled oscillator, 13... Frequency divider, 15... Voltage limiting circuit, 21... Human power terminal, 22... Output terminal.

Claims (1)

[Claims] A time-sharing system in which multiple stations are connected in a loop through a transmission path, the master station generates a clock synchronized with the network clock, each station extracts the clock from the received signal, and each station communicates. In the phase synchronized oscillator that is provided in the master station of the multiplexed loop communication system and generates the clock, voltage limiting means is provided on the input side of the voltage controlled oscillator, so that each station is unable to extract the clock, and communication between each station is prevented. A phase-locked oscillator characterized by preventing failure.