JPS6245741B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an input signal discrimination circuit that discriminates between a voice signal, an intermittent signal such as a busy tone, and a continuous signal. Automatically responds to a call signal from the telephone line,
2. Description of the Related Art A device called an automatic answering machine, which sends a response message to a caller and then records the message from the caller on a recording tape, is in general use. In such devices, the recording time for recording a message from a caller is generally determined by one rotation of the endless tape on which the response message is recorded, or by a timer. In such a method, since the recording time is specified, if the message from the caller is long, it is not possible to record the entire message, causing great inconvenience to the caller. As a method of solving this problem, a circuit called a so-called voice holding circuit has been developed which detects the voice from the caller and maintains the recording state as long as the voice continues. The present invention aims to provide an input signal identification circuit suitable for such a voice holding circuit, and will be described in detail below with reference to the drawings. FIG. 1 is an embodiment of the present invention, and FIGS. 2 to 4 are waveform charts for explaining the operation of the present invention. In the figure, 1 is an input terminal to which a signal is applied, 2 is a variable resistor that adjusts the level of the input signal applied to input terminal 1, and 3 is turned on when the level of the input signal exceeds a predetermined value. A switching transistor 4 is a capacitor that is charged through a resistor 5 when the switching transistor 3 is in an OFF state, and discharged through a resistor 6 and the transistor 3 when the switching transistor 3 is in an ON state. It consists of
Reference numeral 8 denotes a NAND circuit whose output signal level is inverted when the charging voltage of the capacitor 4 constituting the first time constant circuit 7 increases; and 9, an on/off operation is controlled by the output signal of the NAND circuit 8. The transistor 10 is a NAND circuit that outputs a signal obtained by inverting the level of the output signal of the NAND circuit 8. Reference numeral 11 denotes a one-shot multivibrator composed of NAND circuits 12 and 13, a capacitor 14 that determines the inversion operation time, and a resistor 15, and is configured to invert for a predetermined time when the transistor 9 inverts from the off state to the on state. There is. A second time constant circuit 16 is composed of a capacitor 18 that controls the external circuit 17 according to its charging potential, and a resistor 19 that determines the charging time constant. 20 and 21 constitute a NAND circuit 10 and a one-shot multivibrator 11, respectively.
The transistor 2 is a transistor whose on/off operation is controlled by the output signal of the NAND circuit 12 and which forms a discharge path for instantaneously discharging the charge stored in the capacitor 18.
The emitter of transistor 21 is grounded, the collector of transistor 21 is connected to the connection point between capacitor 18 and resistor 19, and the emitter of transistor 21 and the collector of transistor 20 are connected. It should be noted that power is supplied to such a circuit when an input signal identification operation is required. For example, when adopted as a voice holding circuit in an automatic answering machine, the circuit starts operating when power is supplied when the state is switched to recording a message from the caller. The present invention is constructed as described above.Next, each operation for each type of signal applied to the input terminal 1 will be explained with reference to the waveform diagrams of FIGS. 2 to 4. (1) In the case of no signal and low level signal In this case, the switching transistor 3 is in the off state, so when power is supplied, the charging potential of the capacitor 4 constituting the first time constant circuit 7 is changed according to a predetermined time constant. and rise. When the charging potential exceeds the threshold hold (TH) level of the NAND circuit 8, the output of the NAND circuit 8 is inverted from the high H level to the low L level. As a result, the transistor 9, which was in the on state, is reversed to the off state, and its collector potential increases.An H level signal is applied to the input terminal of the NAND circuit 12, which constitutes the one-shot multivibrator 11 . The one-shot multivibrator 11 does not perform an inverting operation, and the output of the NAND circuit 12 remains at the L level. Further, when the output of the NAND circuit 8 is inverted to the L level, the output of the NAND circuit 10 becomes the H level, and the transistor 20 is biased, but the transistor 21 is in the off state. Since no signal higher than a predetermined level is applied to the input terminal 1, the above-mentioned operating state is maintained. Therefore, a discharge circuit for the capacitor 18 constituting the second time constant circuit 16 is not formed, so that the charging potential of the capacitor 18 increases according to a predetermined time constant. When the charging potential reaches a predetermined V level, the external circuit 17 is activated and performs a predetermined operation. (2) Continuous signal case In this case, the switching transistor 3 is kept in the on state by the signal applied to the input terminal 1, so the charging potential of the capacitor 4 forming the first time constant circuit 7 increases. do not. Therefore, the output of the NAND circuit 8 is at H level,
The output of the NAND circuit 10 is at L level, and the transistor 20 is in an off state. Therefore, the charging potential of the capacitor 18 constituting the second time constant circuit 16 increases according to a predetermined time constant, and when the charging potential reaches the V level, the external circuit 17 is activated to perform a predetermined operation. (3) When the off state of the switching transistor 3 is an intermittent signal that is shorter than the predetermined first time (the second
Figure) When the signal shown in Figure 2a is applied to the input terminal 1, the switching transistor 3 turns on.
The off operation is repeated, and the capacitor 4 repeats the charging and discharging operation accordingly. As a result, the potential at point b changes as shown in FIG. 2b, but since the no-signal (low level) period of the input signal is short, the potential does not exceed the TH level.
Therefore, the level of the output point C of the NAND circuit 8 is the second level.
The level of the output point d of the NAND circuit 10 is H as shown in Figure C, the level of the output point d of the NAND circuit 10 is L as shown in Figure 2 d, and the level of the output point f of the NAND circuit 12 configured in the one-shot multivibrator 11 is as shown in Figure 2 f. niL
It is in. Therefore, as in the case of the continuous signal described above, since the transistor 20 is in the off state, the capacitor 18 constituting the second time constant circuit 16
The charging potential increases with a predetermined time constant as shown in FIG. 2g, and when the charging potential reaches the V level, the external circuit 17 is activated to perform a predetermined operation. (4) An intermittent signal in which the switching transistor 3 is inverted to the on state and then inverted to the off state, and the off state is longer than a predetermined first time and the addition time of the on state and off state is shorter than a predetermined second time. (Fig. 3) When a signal as shown in Fig. 3a is applied to the input terminal 1, the switching transistor 3 turns on.
The OFF operation is repeated, but in this case, since the OFF state takes a long time, the charging potential of the capacitor 4 constituting the first time constant circuit 7 exceeds the TH level as shown in FIG. 3B. As a result, the output point c of the NAND circuit 12 constituting the NAND circuits 8 and 10 and the one-shot multivibrator 11 ,
The output levels of d and f change as shown in FIG. 3, c, d, and f, respectively. As is clear from this figure, when a signal such as that shown in FIG . The charge is immediately discharged through transistors 20,21. Therefore, the charging potential of the capacitor 18 changes as shown in FIG. 3g, and does not exceed the V level, so that the external circuit 17 does not operate. (5) An intermittent signal in which the switching transistor 3 is inverted to the on state and then inverted to the off state, and the off state is longer than a predetermined first time and the addition time of the on state and off state is longer than a predetermined second time. (Fig. 4) When a signal as shown in Fig. 4 a is applied to the input terminal 1, the switching transistor 3 turns on.
As the switching transistor 3 repeats the OFF operation, the waveforms of the various parts change as shown in FIGS. 4b to 4f. As is clear from this figure, when a bias is applied to the base of transistor 20, transistor 21 is in an off state, and transistor 2
One-shot multi-vabrator on the base of 1
When the bias is applied by the inversion of 11 , the transistor 20 is in an off state;
Capacitor 1 forming second time constant circuit 16
No. 8 discharge circuit is formed. Therefore, the charging potential of the capacitor 18 rises with a predetermined time constant, and when the charging potential reaches the V level, the external circuit 17 is activated and performs a predetermined operation. As described above, the input signal identification operation of the present invention is performed , but the explanation of each item is as follows: This is a case where a signal is applied to item 1, and the signal of item 4 corresponds to the audio signal. Next, the relationship between input signals and the circuit of the present invention will be explained. The times when the switching transistor 3 is in the on state and the off state are T ₁ and T ₂ , and the charging potential of the capacitor 4 constituting the first time constant circuit 7 is
The time it takes to reach the TH level is _t1 , and the reversal operation time of the one-shot multivibrator 11 is
t ₂ , 4 if the discharge time constant of capacitor 4 is t ₀
The conditions under which the external circuit 17 does not operate as described in Section 1 are t ₁ ≦T ₂ , T ₁ +T ₂ <t ₂ −t ₁ , and t ₀ <T ₁ . In this embodiment, the one - shot multivibrator 11
Although in the above embodiment, the voltage is reversed, it is also possible to reverse the voltage by changing the voltage from less than a predetermined potential to a predetermined potential. It is also possible to use the discharging time constant of the capacitor 4 instead of the charging time constant. Furthermore, a capacitor 1 constituting the second time constant circuit 16
Although the discharge circuit No. 8 is formed by transistors 20 and 21, logic elements may also be used. As explained above, the input signal identification circuit of the present invention not only can distinguish between audio signals, intermittent signals such as busy tones, and continuous signals, but also has a configuration that allows external circuits to be A discharge path that instantaneously discharges the electric charge stored in the capacitor is controlled by the charging potential of the capacitor whose charging potential changes according to the input signal and the output signal of the inverting circuit which is inverted for a predetermined time due to the change in the potential of the capacitor. Since I made it to control, the second
The time required for the charging potential of the capacitor of the time constant circuit to reach a predetermined value and the external circuit to operate can be made constant, and the present invention is most suitable as a voice holding circuit for an automatic answering machine.

[Brief explanation of the drawing]

FIG. 1 is an embodiment of the present invention, and FIGS. 2 to 4 are waveform charts for explaining the operation of the present invention. Explanation of main figure numbers 3...Switching transistor, 7 ...First time constant circuit, 11 One-shot multivibrator, 16 ...Second time constant circuit.

Claims (1)

[Claims] 1. A first time constant circuit including a switching transistor that performs on/off operations according to an input signal, a capacitor that is repeatedly charged and discharged by the on/off operations of the switching transistor, and the first time constant circuit. An inverting circuit that inverts when the charging potential of the constituting capacitor changes from above to below a predetermined potential or from below to above, and maintains that state for a predetermined period of time, and an external circuit that operates when the charging potential reaches a predetermined value due to charging operation. a second time constant circuit including a capacitor for discharging the second time constant circuit; and first and second time constant circuits provided in the discharge path for instantaneously discharging the charge of the capacitor constituting the second time constant circuit when both are in an on state. a switching element, which controls the on/off operation of the first switching element by changing the charging potential of the capacitor constituting the first time constant circuit, and controls the on/off operation of the second switching element by the inverting circuit. An input signal identification circuit characterized in that it is controlled by an output signal of.