JPH0458732B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a signal switch for automatically switching between two clock signal sources in order to reduce the probability of failure.

Configuration of a conventional example and its problems FIG. 1 shows a conventional signal switching device, and the configuration of the conventional example will be explained below with reference to FIG. 1.

In Figure 1, A _{1 and} A ₂ are signal generators, B ₁ and B ₂
is a signal switch, C ₁ , C ₂ are level comparators, D ₁ ,
_D2 is a signal detector, E is a switching controller, F is a changeover switch, G is a signal combiner, H is an output terminal, and J is a reference voltage.

Next, the operation of the above conventional example will be explained. Each of the signal generators A ₁ and A ₂ oscillates at a predetermined frequency. This output is output from the signal detector D ₁ ,
It is detected by D ₂ and compared by level comparators C ₁ and C ₂ to see if it is higher than the reference voltage J, and is output to the switching controller E as 1,0 information. Switching controller E
sends a control signal to switch B ₁ and B ₂ according to the ON/OFF information of switch F to generate a signal generator.
It is configured to output the signal of A ₁ or A ₂ to the output terminal H via the combiner G. In this way, the signal switcher has two signal generators _A1 and
If switch F is turned on or off when _A2 is operating, either analog switch _B1 or _B2 is turned on and output is output to terminal H via synthesizer G.

In the conventional signal switcher mentioned above, the signal detector
Since D ₁ and D ₂ detect the signal level by smoothing the detection voltage and compare it with the reference voltage J, they have the drawback of causing a considerable delay in detecting signal disconnection. Especially when using this signal as a reference signal for a frequency synthesizer, synchronization may occur during signal switching,
When used as a local oscillator in an FM receiver, it generates a large click noise. In addition, in the case of transmission, there was a drawback in that it caused interference signals to adjacent channels and more channels.

Purpose of the Invention The present invention eliminates the drawbacks of the above-mentioned conventional example, and smoothly performs signal switching by detecting the loss of signal frequency within an extremely short period of time and switching to the signal of the paired oscillator. The purpose is to

Structure of the Invention In order to achieve the above object, the present invention divides the frequencies of two sets of temperature compensated crystal oscillators (hereinafter referred to as TCXOs) individually and guides them to an output synthesizer when creating a reference frequency for a frequency synthesizer. At the same time, part of this output is given to the paired oscillator, the presence or absence of this signal frequency is detected in a very short period of time, and if the signal output of the paired oscillator is cut off, the signal of the other oscillator is immediately transmitted. It is possible to provide a signal switching device that maintains loss of signal output within one cycle.

DESCRIPTION OF EMBODIMENTS The configuration of an embodiment of the present invention will be described below with reference to the drawings.

In FIG. 2, 21 and 22 are signal generators;
23 is a switch or combiner for the signals of the signal generators 21 and 22; 24 is an alarm that indicates a failure in the signal generator; and 25 is a switch that determines the initial operation of the signal generators 21 and 22. Further, in the signal generators 21 and 22, 211 and 221 are signal output terminals, 212 and 222 are signal branch output terminals, and 21
3 and 223 are alarm output terminals, 214 and 22 are switching signal terminals, 215 and 225 are branch input terminals of a pair of signal generators, 216 and 226 are fault signal terminals, 217 and 227 are fault signal input terminals, and 231 and 232 are signal input terminals, 233 is a signal output terminal, 241 and 242 are alarm information input terminals, 251 and 252 are switching information terminals, and 253 is a switch terminal, which are connected to ground or a voltage source as shown in the figure. ing.

When the two signal generators 21 and 22 are in operation, the changeover switch 25 is connected to the terminal 251, and signals are output from the terminals 211 and 212 of the signal generator 21, and the output from the terminal 221 is connected to the changeover switch 23.
It enters the terminal 231 and outputs from the terminal 233.
The output from the terminal 212 is input to the input terminal of the signal generator 22 as output information. In this case, the signal output from the output terminals 221 and 222 of the signal generator 22 is disconnected. Terminals 213 and 223 output electrical information indicating the operating status of signal generators 21 and 22. Further, in the case of a failure, an alarm signal is sent to at least the alarm 24 to generate an alarm sound.

Now, when the signal from the signal generator 21 is cut off, the signal output from the terminals 211 and 212 is cut off, and the signal output from the terminal 225 is cut off.
The input signal is also cut off. When the signal generator 22 detects this signal output interruption, it immediately turns on the switch and outputs its own signal from the terminals 221 and 222. The signal from terminal 221 enters the switch or combiner 23 and is output from terminal 233. This switching is performed in a short time within one cycle of the signal frequency.

FIG. 3 shows an embodiment of a circuit for realizing the functions of the signal generators 21 and 22 shown in FIG. In the figure, Vcc is a power supply voltage, and 1 is a temperature compensated crystal oscillator, which has high accuracy and high frequency stability against changes in ambient temperature, and generates a frequency f ₀ . 2
and 5 are inverters, and 3 is a frequency counter that lowers the input frequency f ₀ to 1/2 ⁿ . Frequency counter 3
For example, f ₀ /2 ⁵ is output from the output Q ₅ terminal, and f ₀ /2 ⁸ signal output f ₅ is output from the Q ₈ terminal. 4 is an analog switch, and _R3 is a series resistor. The signal output control section includes monostable multivibrators 6, 7 that can be reset and triggered, high gain transistor elements 8,
OR gates 9, 11, 12, capacitors C ₁ , C ₂ ,
It is composed of resistors R ₁ and R ₂ , and C ₁ , R ₁ and C ₂ , R ₂ determine the time constants of the monostable multivibrators 6 and 7.

Next, the operation of the above circuit will be explained.

The output frequency f ₀ of the oscillator 1 is turned into a rectangular wave by the inverter 2, and is added to the counter 3, which performs the required frequency division and outputs the frequency-divided signals from Q ₅ and Q ₈ . The output of terminal Q ₈ becomes the reference frequency f _S supplied to subsequent equipment. In this case, the output of Q ₅ is 2 ³ · f _{S. Q8} output is analog switch 4
When is ON, the signal is shaped by the inverter 5 and output to the terminals 211 and 212 through the series resistor _R3 .
The output of Q ₅ , frequency 2 ³ · f _S , enters the monostable multivibrator, and when there is an output on Q ₅ , the Q output of monostable multivibrator 6 is H, and the output of alarm output terminal 213 is inverted by inverter 8. becomes L and does not issue an alarm. C ₁・R ₁ is the input frequency
2 ³ · f It is set below ₀ , and when the input frequency stops, the Q output is inverted and the alarm is activated.
At the same time, Q becomes H, inverting the OR gate 11, inverter 10, and OR gate 9, and turning off the analog switch 4. The Q output of the monostable multivibrator 6 is transmitted through the inverter 13 to 21
6 and terminal 2 of the pair of signal generators 22.
27, the OR gate 12 is inverted, the OR gate output is set to H, and the analog switch 4 is turned ON. As a result, the output frequency f _S ' of Q ₈ of the frequency counter 3 on the signal generator 22 side is outputted to 221 .
The detection time of signal disconnection of monostable multivibrator 6 is t _S = 1/ when C ₁・R ₁ is selected as 2 ³・f _S
TCX01 failure was discovered in 1/8 time of f _S , and this information was sent to the signal generator side of the pair to terminals 216 and 217.
These circuit elements 12,
Even if the total operating time of 9 and 4 is several μs, switching to the output of the pair of signal generators 1 can be performed in a fraction of the time of 1/f _S .

Note that the terminal 214 outputs the analog switch 4 with priority when the input is L. Furthermore, if the reference signal f _S from the terminal 212 on the signal generator 21 side is cut off for some reason, for example, due to a failure in the analog switch 4, inverter 5, or series resistor _R3 ,
After a time determined by the time constant of C ₂ and R ₂ of the monostable multivibrator 7 (for example, t _S = 1/f _S ), output is output from Q, and the analog switch 4 is turned ON by the OR gates 12 and 9 to set the reference frequency. f _S ′ to terminal 22
Send from 1. Time required for switching in this case
t _S ' becomes t _S '>1/f _S , but even in such a case, it is possible to switch to a pair of signal generators within two cycles of the reference frequency f _S . Note that the monostable multivibrators 6 and 7 constitute a first and second monitoring circuit, respectively, and the OR gates 9, 11, and 12 and the inverter 10 constitute a signal output control circuit. Therefore, the signal output control section includes first and second monitoring circuits, a signal output control circuit, and the like.

Effects of the Invention The present invention has the above-described configuration, and provides the following effects.

(a) The reference frequency f _S is created by dividing the frequency f ₀ of TCX0, but a signal of 2 ⁿ f _S is extracted several stages before obtaining f _S , and this is used to detect missing cycles. , the frequency of the pair of signal generators is transmitted, so a stable signal can be transmitted in a fraction of the time of one cycle of the reference frequency _fS .

(b) The output of the signal generator may fall below the reference frequency due to a fault in the circuit and circuit elements after the analog switch.
When f _S is cut off, a stable signal can be sent at least for a time f _S ′ close to one cycle of f _S .

[Brief explanation of the drawing]

Figure 1 is a block diagram showing a conventional signal switching device.
FIG. 2 is a block diagram showing an embodiment of the signal switching device of the invention, and FIG. 3 is a circuit diagram showing a specific example of the configuration of the signal switching device of the invention. 1... Oscillator, 3... Frequency counter, 4...
Analog switch, 6, 7... Monostable multivibrator, 21, 22... Signal oscillator, 23...
Switcher or combiner, 24...Alarm, 25...
...Switch.

Claims (1)

[Claims] 1 comprises a pair of signal generators and a synthesizer that switches and combines their outputs to output one of the signals generated by the pair of signal generators, and each of the signal generators forming the pair , a highly stable frequency oscillator, a frequency divider for dividing the output of the frequency oscillator to obtain a reference signal frequency output and a monitoring output 2 ⁿ times (n is an integer) the reference signal frequency; a signal switch circuit for controlling the output of the reference signal frequency to obtain one output of the signal generator; and a first signal switch circuit for monitoring the monitoring output and sending a fault signal to the other signal generator in the pair. a second monitoring circuit that monitors the output of the reference signal frequency and the fault signal from the other signal generator of the pair; A signal switch consisting of a signal output control circuit that determines the operation of the switch circuit.