JPH03267827A - Signal detection circuit - Google Patents

Abstract

PURPOSE:To surely detect an idle channel without mis-judgement due to noise by providing a 1st detection means outputting a 1st detection signal in the detection of a transmission signal, a 2nd detection means outputting a 2nd detection signal after the lapse of a prescribed time and an AND gate between the 1st detection signal and the 2nd detection signal. CONSTITUTION:This circuit is provided with the 1st detection means 10 outputting the 1st detection signal in the detection of a transmission signal, the 2nd detection means 12 outputting the 2nd detection signal after the lapse of a prescribed time and a discrimination means 15 outputting a discrimination signal in the case of receiving both the 1st detection signal and the 2nd detection signal. In this case, when a consecutive transmission signal is present thereon, the 1st detection signal is outputted from the 1st detection means 10 and the 2nd detection signal is outputted from the 2nd detection means 10 with the delay of a prescribed time. Thus, in the case of pulse noise, the 1st and 2nd detection signals are not simultaneously outputted, the output of a deciding signal from a deciding means 15 is avoided and then an idle channel is surely detected.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a signal detection circuit for detecting the presence or absence of a transmission signal, and particularly to a signal detection circuit suitable for use in detecting an empty channel in a cordless telephone.

``Prior Art'' When making a call using a cordless telephone, it is necessary to detect in advance an empty channel from among a plurality of shared channels and allocate it to the own station. An example of a circuit for detecting this empty channel will be explained with reference to FIG.

In the figure, l is a microcomputer that supplies a channel command signal Se to the local oscillator 2 for selecting an arbitrary channel among the shared channels. Local oscillator 2 generates a sine wave with a frequency based on this channel command signal Sc, and supplies it to first frequency mixer 3. On the other hand, high frequency signals of various channels are supplied to the first frequency mixer 3 via an antenna 4. Here, the channel command signal S. When a high frequency signal corresponding to 1 is supplied to the first frequency mixer 3, this high frequency signal is mixed with the output signal of the local oscillator 2 to undergo frequency conversion and is supplied to the second frequency mixer 5.

In the second frequency mixer 5, the frequency-converted high-frequency signal and the output signal of the local oscillator 6 are mixed, and the frequency-converted high-frequency signal is converted into an intermediate frequency signal.

This intermediate frequency signal is subjected to FM detection in the FM detector 7 and converted into an audio frequency signal.

Further, 8 is an active filter, and its pass frequency band is set to about 10 kHz so that only high frequency components of the audio frequency signal are passed. Therefore, only the high frequency component of the audio frequency signal output from the FM detector 7 is supplied to the rectifier circuit 9. This high frequency component is rectified in the rectifier circuit 9 and supplied to one input terminal of the comparator 10 as a detection signal Sl.

On the other hand, a predetermined threshold voltage V is applied to the other input terminal of the comparator IO by a constant voltage source IJ. The comparator 10 compares the magnitude relationship between the detection signal S1 and the threshold voltage V, and outputs a binary logic signal S! which becomes "H" if the former is large and "L" if the latter is large. Here, the threshold voltage V
, are set in advance to a level slightly lower than the level of the detection signal S1 when the carrier component is present.

Therefore, if the channel selected by the channel command signal Sc is in use, a carrier wave exists in that channel, so the signal St becomes "1-1"; on the other hand, if that channel is not used, a carrier wave exists. Since it does not, the signal St.

Then, if the signal S is "L", the microcomputer 1 assigns that channel to its own communication channel.
", the microcomputer I outputs a channel command signal S0 corresponding to another channel, and it is determined in the same way as above whether or not that channel is in use. In this way, if an empty channel is The channel corresponding to the channel command signal Se is changed until the channel command signal Se is found, and the signal Sf is monitored by the microcomputer 1.

``Problems to be Solved by the Invention'' By the way, since cordless telephones are used in various environments, pulse-like external noise as shown in FIG. 4, for example, is superimposed on the detection signal S1, and the detection Signal S
The level of l may exceed the threshold voltage V. and,
Within the period in which the detection signal S1 exceeds the threshold voltage ■ (from time L1 to
11), the output signal S of the comparator IO becomes "Ho". In this case, according to the configuration of FIG.
If the signal S is input to the microcomputer 1 within the period , it is determined that the channel being monitored is in use even if the channel is not in use.

In recent years, the number of cordless telephones has been steadily increasing.
It is expected that there will be a shortage of free channels in the future. Under these circumstances, according to the configuration shown in Figure 3,
There was a problem in that it was easy to lose line connection opportunities due to misjudgment, and empty channels could not be used effectively.

The present invention has been made in view of the above-mentioned circumstances, and it is an object of the present invention to provide a signal detection circuit that can accurately detect empty channels.

"Means for Solving the Problems" In order to solve the above problems, the signal detection circuit according to the present invention has the following features:
a first detection means that outputs a first detection signal when a transmission signal is detected; a second detection means that outputs a second detection signal after a predetermined time has elapsed when a transmission signal is detected; and the first detection signal and a determining means that outputs a determining signal when both the detection signal and the second detection signal are input.

"Operation" In a situation where there is a continuous transmission signal, when the first detection signal is output from the first detection means, the second detection signal is transmitted from the second detection means after a predetermined time delay. A signal is output. Therefore, after a predetermined period of time has elapsed since the transmission signal was generated, both the first detection signal and the second detection signal are output, so that the determination means outputs the determination signal.

On the other hand, when pulse-like noise is input to the first and second detection means, the first and second detection signals are output even when no transmission signal is present. However, by setting the predetermined time in the second detection means to be longer than the pulse width of the noise, the first and second detection signals will not be output at the same time, and the determination signal will not be output from the determination means. Avoided.

"Embodiment" Next, an embodiment of the present invention will be described with reference to FIG. In the figure, parts corresponding to those in FIG. 3 are given the same reference numerals, and their explanations will be omitted.

In the figure, the output terminal of the rectifier circuit 9 is connected to one input terminal of a comparator IO, and is also connected to one input terminal of a comparator 14 via an integrating circuit consisting of a resistor 12 and a capacitor 13. Further, a threshold voltage 1 is applied to the other input terminals I of the comparators 10 and 14 by a constant voltage source 11. Therefore, when the signal S3, which is the terminal voltage of the capacitor 13, becomes greater than the threshold voltage V, the output signal S4 of the comparator I4 becomes "H". Further, 15 is an AND gate, and the signal S! The logical product of and signal S4 is signal S.

Output as .

Similarly to FIG. 3, the microcomputer 1 receives signals S,
If the signal S is “H”, it is determined that the channel corresponding to the channel command signal Se is in use, and the signal S is “L”.
”, it is determined that the channel is not in use.

Next, the operation of this embodiment will be explained with reference to FIGS. 2(A) to 2(E).

When the channel selected by the channel command signal Sc is not in use and pulse noise is present,
The detection signal S1 is a substantially triangular pulse as shown in FIG. 2(A), and becomes larger than the threshold voltage V within the time period 1, -1. Therefore, as shown in the same figure (c), the signal S during this period becomes °H.
As shown in FIG. 4B, the signal S, which is an integral signal of the detection signal S, is greater than the threshold voltage V during the period of time ˜L. Therefore, as shown in FIG. 4(d), the signal S4 becomes "H" during this period.

Here, if the time constant of the integrating circuit consisting of resistor 12 and capacitor 13 is set sufficiently large, time t1 to t,
The time T can be made longer than the time t, ~t. In this case, as is clear from (c) to (e) of the same figure, since the signals St and S4 never become "H" at the same time, the signal S always becomes "L".

On the other hand, when the channel is in use, the detection signal S1 continues at a level higher than the threshold voltage V for a long time, so the signal S3 also continues at a level higher than the threshold voltage V, and the signals St, S4 together become “Tobi,” and as a result,
Of course, the signal S becomes "H".

As described above, in this embodiment, even if pulse noise is present in an empty channel, the signal S does not become "H", and therefore, an empty channel is accurately detected.

Note that the present invention is not limited to the above-mentioned embodiments, and various modifications are possible. For example, the circuit that delays the detection signal S1 is a resistor! A configuration other than the integrating circuit consisting of 2 and capacitor 13 may be used. Also, omit this integration circuit and use a comparator! It goes without saying that a digital delay circuit may be inserted after the signal S4 to delay the signal S4.

"Effects of the Invention" As explained above, according to the signal detection circuit of the present invention, the first detection means outputs the first detection signal when the transmission signal is detected, and the second detection means outputs the first detection signal after a predetermined time has elapsed when the transmission signal is detected. Since the second detection means outputs a detection signal and the determination means outputs a determination signal when both the first detection signal and the second detection signal are input, there is no misjudgment due to noise. Empty channels can be detected accurately.

[Brief explanation of drawings]

Figure 1 is a block diagram of a signal detection circuit according to an embodiment of the present invention, Figure 2 is a waveform diagram of each part of Figure 1, Figure 3 is a block diagram of a conventional signal detection circuit, and Figure 4 is a block diagram of a signal detection circuit according to an embodiment of the present invention. is a waveform diagram of the signal S1 in FIG. 3. 10... Comparator (first detection means), 12...
・Resistor (second detection means), 13... Capacitor (second detection means), 14... Comparator (second detection means), 15... AND gate (Judgment means)
.

Claims (1)

[Claims] A first detection means that outputs a first detection signal when a transmission signal is detected; a second detection means that outputs a second detection signal after a predetermined time has elapsed when a transmission signal is detected; A signal detection circuit comprising: determination means that outputs a determination signal when both the first detection signal and the second detection signal are input.