JPH01321374A - Input signal alarm circuit - Google Patents

Abstract

PURPOSE:To enable the setting of a large level for an alarm generation threshold by connecting inputs of two amplifiers to respective IN terminals while an output of one amplifier is connected to two inputs of an analog switch circuit. CONSTITUTION:An input terminal IN is connected to an output terminal OUT through first and second amplifiers 1 and 2. Outputs A and B of the amplifiers 1 and 2 are applied respectively to inputs 1 and 2 of an analog switch circuit 3. An output of the circuit 3 is connected to an output terminal T2 through a signal amplitude detection circuit 4 and an external control terminal T1 is drawn from the circuit 3 separately. When an input signal amplitude level at which an input signal alarm is expected to generate is different, gains of the amplifiers 1 and 2 are set for the terminal IN considering this to use the circuit 3 which allows selectively outputting of an input signal at the terminal T1. Then, an appropriate signal amplitude is inputted into the circuit 4 thereby facilitating the adjustment of an alarm generation threshold.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an input signal alarm circuit, and particularly to an input signal alarm circuit including an amplifier, an analog switch circuit, a signal amplitude detection circuit, and the like.

[Conventional technology]

A conventional input signal alarm circuit will be explained with reference to FIG. In the same figure, the input of the first amplifier 10 is connected to the input terminal IN, and the output terminal of the first amplifier 10 is connected to the input terminal of the second amplifier 20. The output of the second amplifier 2- is connected to the output terminal OUT and the input of the signal amplitude detection circuit 40,
The signal amplitude detection circuit 4 is connected to an external adjustment terminal ADJ,
It is also connected to the output terminal T2. With the above configuration, if a large number of sine waves with sufficiently large amplitudes that have been timing-shaped by a dimming filter or the like are input to the input terminal IN,
amplified by the first and second amplifiers 1 and 2;
Outputs a signal from the output terminal OUT. On the other hand, when the input signal amplitude is small, the output of the second amplifier 2 does not operate as a limiter, and the signal is input to the signal amplitude detection circuit 4 in a so-called sunar region operation. The input signal described above is peak-rectified inside the signal amplitude detection circuit 4, and compared with a threshold value vth from the terminal ADJ, which is set in advance to generate an alarm, to identify the presence or absence of the signal, and to determine whether the input signal level is An alarm signal is generated when the value is smaller than the threshold value vth.

FIG. 6 is a characteristic diagram showing the relationship between the output waveform B of the second amplifier 2 and the alarm generation threshold value vth at this time. In the same figure, the upper and lower hatched limiter areas are the second
shows the saturation region of the output of amplifier 2, and the actual output signal exists in the region surrounded by this.The dotted line indicates the saturation region of the output of amplifier 2.
I, the solid line is the output signal ■o.

FIG. 7 is a characteristic diagram showing the relationship between the above-mentioned alarm generation threshold Vth and the output terminal T2 of the signal amplitude detection circuit 4.

[Problem to be solved by the invention]

In the conventional input signal alarm path described above, if the amplitude of the signal input to the input terminal IN differs due to the difference in the sign of the signal or the mark rate of the signal, for example, C
In the case of the MI code or NRZ code, the setting of the alarm generation threshold value vth of the signal amplitude detection circuit 4 that is scheduled to generate an alarm is determined within the output dynamic range of the second amplifier 2 described above. In other words, if the gain of the limiter amplifier section is constant, when the signal amplitude input to the input terminal IN is large (in the case of characteristic curve 5), a signal alarm will occur within the range where the output of the second amplifier 2 does not operate as a limiter. It is necessary to set a threshold value Vth. Conversely, when the input signal amplitude becomes smaller than the above (in the case of characteristic curve 6),
For example, when the aforementioned mark rate of the signal becomes smaller, the aforementioned signal alarm occurrence threshold Vth also becomes smaller, so it is necessary to reset the signal alarm occurrence threshold Vth to a smaller threshold value V th' using the external adjustment terminal ADJ. There is. At this time, the signal amplitude detection circuit 4 described above has the disadvantage that it is susceptible to the influence of external noise because it detects a smaller value, and that the external adjustment described above is difficult.

SUMMARY OF THE INVENTION An object of the present invention is to provide an input signal alarm circuit which eliminates the drawbacks of the conventional input signal alarm circuit described above and which makes it easy to adjust the alarm generation threshold Vth.

[Failure to solve the problem]

The configuration of the present invention includes amplifiers connected in at least two or more stages, an analog switch circuit that selects and outputs at least two input signals, and a signal amplitude detection circuit that identifies the input signal amplitude and outputs an alarm signal. In the input signal alarm circuit, the input of the first of the amplifiers is connected to the IN terminal, the output is connected to the first input of the analog switch circuit described above, and the input of the second amplifier is connected to the first input. connected to the output of the amplifier, said second amplifier 2
The output of the analog switch circuit is connected to a second input of the analog switch circuit, the output of the analog switch circuit is connected to the input of the signal amplitude detection circuit described above, and the analog switch circuit is connected to an external control terminal. Ao characterized by [Example] Next, the present invention will be described with reference to the drawings.

FIG. 1 is a diagram of an input signal alarm circuit according to a first embodiment of the present invention, and parts equivalent to those in FIG. 5 are designated by the same reference numerals. In the 11th station, the circuit of this embodiment has the input terminal IN connected to the first amplifier 1 through the second amplifier 2.
Connected to the output terminal OUT. On the other hand, the output A of the first amplifier 1 is applied to the input 1 of the analog switch circuit 30, the output B of the second amplifier 2 is applied to the input 2 of the analog switch circuit 3, and the output A of the first amplifier 1 is applied to the input 1 of the analog switch circuit 30. 3 is connected to a signal amplitude detection circuit 4, and the output of this signal amplitude detection circuit 4 is connected to an output terminal T2.
The control terminal T1 is connected to the analog switch circuit 3 described above.

In such a configuration, as shown in FIG. 2 (ta+), when the input signal level at which the alarm is to be set becomes low, as shown in FIG. First, the output +Bl of the second amplifier 2 is input to the input 1 of the analog switch circuit 30 in the so-called IJ near region, and as shown in FIG. input 1 of the analog switch 3 is selected by the external adjustment terminal T1, and is input to the signal amplitude detection circuit 4,
It is compared with the alarm setting threshold value Vth of this signal amplitude detection circuit 4 to identify the presence or absence of an alarm. Next, as shown in FIG. 2(d), when the input signal level for which the alarm is to be set is small, the outputs of the first and second amplifiers 1 and 2 (B
) does not operate as a limiter (Fig. 2 (e), Fig. 2)), and is input to input 1 and input 2 of the analog switch circuit 3 described above in the linear region, and the analog switch is controlled by the external adjustment terminal T1. The input 2 of the circuit 3 is selected and input to the signal amplitude detection circuit 4, where it is compared with the above-mentioned alarm setting I# value vth.

In this way, in this embodiment, when the input signal amplitude levels at which an input signal alarm is scheduled to occur are different, the gains of each amplifier 1 and 2 are set in consideration of this, and the gain of each amplifier 1 and 2 is set to By using the analog switch circuit 3 that can selectively output the human signal, an appropriate signal amplitude is inputted to the signal amplitude detection circuit 4, and the alarm generation threshold value vth can be easily adjusted.

FIG. 3 is a block diagram showing an input signal alarm circuit according to a second embodiment of the present invention. In the same figure, this example shows
The difference from the first embodiment is that a K IJ transmitter amplifier 7 is further connected after the second amplifier 2, but a configuration in which a clock signal is output is also possible.

FIG. 4 is a block diagram of a third embodiment of the present invention. In the figure, in this embodiment, the amplifier has an N-stage configuration, and the analog switch circuit 30 has N inputs, so that N selections can be made.

〔Effect of the invention〕

As explained above, the present invention sets the gain of the amplifier in each stage especially when the level of the input signal for which an alarm is to be set is different, and adjusts the signal amplitude to an appropriate signal amplitude by controlling the external adjustment terminal of the analog switch circuit. Since the input signal can be input to the detection circuit, the level setting of the alarm generation threshold vth can be increased regardless of the magnitude of the input signal, reducing the influence of external noise and creating a more stable input signal alarm circuit. There are benefits to be gained.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of the input signal alarm circuit according to the first embodiment of the present invention, Fig. 2 t8) to Fig. 2) are waveform diagrams showing the operation of the circuit in Fig. FIG. 4 is a block diagram of an input signal alarm circuit according to a second embodiment of the invention, FIG. 4 is a block diagram of an input signal alarm circuit according to a third embodiment of the invention, and FIG. 5 is a block diagram of a conventional input signal alarm circuit. ,
6 and 7 are both a waveform diagram and a characteristic diagram showing the operation of the circuit of FIG. 5. 1...First amplifier, 2...Second amplifier, 3...Analog switch circuit, 4...
... Signal amplitude detection circuit, 5, 6 ... Characteristic curve, 7 ... Limiter amplifier, IN ... Input terminal, OU'l'' ... Output terminal, vth...
...Input signal alarm setting threshold, ADJ...
・External adjustment terminal, T1...External control terminal, T2
...Alarm output terminal. Agent Patent Attorney Uchihara Narukai 3wI etc. 41M Kaya 2 rg! J(tl) 92 M(b>
92 Leap (c) JP 2 m(d)
! , 2 11J(e) ¥-2 yen U) Difference! ; Ronre Otsu Figure # 7 1! I

Claims (1)

[Claims] Amplifiers connected in at least two stages, and at least two
In the input signal alarm circuit, the input signal alarm circuit includes an analog switch circuit that selects and outputs one or more input signals, and a signal amplitude detection circuit that identifies the amplitude of the input signal and outputs an alarm signal. An input of a first amplifier is connected to an input terminal, an output is connected to a first input of the analog switch circuit, an input of a second amplifier is connected to an output of the first amplifier, and an output of the second amplifier is connected to an input terminal of the analog switch circuit. is connected to a second input of the analog switch circuit, an output of the analog switch circuit is connected to an input of the signal amplitude detection circuit, and the analog switch circuit has an external control terminal. circuit.