JPH1023081A - Signal detection circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize the signal detection circuit in which detection accuracy of a synchronizing signal is improved and a filter circuit is simplified. SOLUTION: This circuit is configured to detect a signal, having a specific frequency component and a DC component. An output of a narrow-band filter 101, tuned to a specific frequency component, is compared with a 1st threshold level th1 at a 1st comparator circuit 103, and an output of a mean-value- detection circuit 102 extracting a mean value of an input signal with two high/ low 2nd and 3rd threshold levels th2, th3 at a 2nd comparator circuit 104. When it is discriminated that an output of the narrow band filter 101 exceeds the 1st threshold level th1 and an output of the mean value detection circuit 102 is resident between the 2nd threshold level th2 and th 3rd threshold level th3, it is discriminated that a signal is detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal detection circuit for detecting a detected signal having a specific frequency component superimposed on a DC component from an input signal.

[0002]

2. Description of the Related Art In various communications, when establishing synchronization between transmission and reception and transmitting information by a signal using a specific frequency, a specific frequency component is selected from signals having noise and various frequency components. Must be extracted.

In such a case, extraction is often performed using a narrow band filter tuned to the frequency component, and such a circuit is usually called a tank circuit. The output of the tank circuit is
It is expected that the output amplitude will increase when a signal containing the component of the specific frequency fc is input, and that the output amplitude will decrease sufficiently in other cases.

FIG. 6 shows an example of a conventional signal detection circuit using a tank circuit. A detected signal of a specific frequency is extracted from an input signal using a narrow band filter 101, and the extracted output is set to a threshold value th.
1 and the comparator 103. If the extracted output is larger than the threshold th1, it is determined that the detected signal has been input to the determination circuit 105.

FIG. 7A shows an example of the frequency response of the narrow band filter 101 used in such a tank circuit, and FIG. 7B shows an example of the time response of the narrow band filter 101. It is shown. Here, the narrow-band filter 101 is adjusted so that components within the band of fc ± Δf pass to some extent, and components outside the band are suppressed. The width of Δf and the amount of suppression of out-of-band components differ depending on the configuration method of the filter. Δf / fc is called a Q value. For a same center frequency, when the Q value increases, Δf decreases and the amount of suppression of out-of-band components increases. In terms of time, the response time increases as the Q value increases.

By the way, when it is intended to supplement a synchronous signal containing a specific frequency component, for example, a threshold is applied to the output amplitude of the narrow band filter 101 in order to distinguish the synchronous signal from noise and signals other than the synchronous signal. It is assumed that a synchronization signal is received when the filter output amplitude of the narrow band filter 101 exceeds the threshold.

Here, when a filter having a small Q value is used as the narrow-band filter 101, the narrow-band filter 101 is a low-order filter, so that the required circuit scale is small. When a signal other than the above is received with a large input, the output of the narrow band filter 101 may exceed the threshold th1, and it may be erroneously recognized that a synchronization signal has been received.

If the Q value of the narrow-band filter 101 is increased in order to increase the amount of suppression of the out-of-band component in order to avoid this erroneous recognition, the filter response time becomes longer accordingly. Therefore, when the duration of the synchronization signal is short, the synchronization signal ends before the output of the narrow band filter 101 exceeds the threshold value th1, resulting in a problem that the synchronization signal cannot be captured. In this case, since the order of the filter must be increased, there is a problem that the circuit scale is increased.

In addition, some known DC components are superimposed on signals containing such frequency components. In the conventional method using a tank circuit as shown in FIG. This is configured to be removed by the narrow band filter 101 including the above.

[0010]

As described above, in the conventional invention, a detected signal having a specific frequency component superimposed on a DC component is detected by a tank circuit as shown in FIG. In order for the narrow band filter 101
Has to be large, so that the circuit configuration is complicated and the duration of the synchronization signal needs to be long.

If the Q value of the narrow-band filter 101 is increased in order to increase the amount of suppression of out-of-band components in order to avoid this erroneous recognition, the filter response time becomes longer accordingly. Therefore, when the duration of the synchronization signal is short, the synchronization signal ends before the output of the narrow band filter 101 exceeds the threshold value th1, resulting in a problem that the synchronization signal cannot be captured.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a signal detection circuit capable of reliably detecting a detected signal having a specific frequency component superimposed on a DC component.

[0013]

To achieve the above object, the present invention provides a signal detection circuit for detecting a detected signal from an input signal including the detected signal having a specific frequency component superimposed on a DC component. A narrow-band filter tuned to the specific frequency component, a first comparison circuit that compares an output of the narrow-band filter with a first threshold, and an average value detection circuit that extracts an average value of the input signal. A second comparison circuit that compares the output of the average value detection circuit with two high and low second and third threshold values, and the output of the narrow band filter is larger than the first threshold value by the first comparison circuit. And a determination circuit for determining that the detected signal is detected when the output of the average value detection circuit is determined to be between the second and third thresholds by the second comparison circuit. Characterized by

Here, the narrow band filter can be constituted by a digital filter. This digital filter can be composed of a second-order IIR (infinite impulse response filter) filter.

According to the present invention, the output of the narrow-band filter is larger than the first threshold value by the first comparison circuit, and the output of the average value detection circuit is the second and the third by the second comparison circuit. Since it is configured to determine that the detected signal has been detected when it is determined that the detected signal is within the third threshold value, the detected signal having a specific frequency component superimposed on the DC component included in the input signal Can be detected reliably and with high accuracy.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the signal detection circuit according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram of an embodiment of a signal detecting circuit for determining a signal to be detected having a specific frequency component fc superimposed on a DC component according to the present invention.

The circuit shown in FIG. 1 will be described.

In the block diagram of this signal detection circuit, 101
Is a narrow-band filter tuned to the frequency fc of the AC component of the signal to be detected, 102 is an average detector for calculating the average value of the reception level of the received signal, 103 is whether or not the output 1a of the narrow-band filter 101 is greater than or equal to the threshold th1 Are comparators (1) and 104 which determine whether or not the average value of the reception level, which is the output 1b of the average value detector 102, is between the threshold th2 and the threshold th3. Reference numeral 105 denotes a determination circuit that determines a signal to be detected having a specific frequency component fc superimposed on a DC component since both the output 1c of the comparator (1) 103 and the output 1d of the comparator (2) 104 are true. is there.

When a signal to be detected having a specific frequency component fc superimposed on a DC component is input to the signal detection circuit, an AC signal having a frequency fc is output to the output 1a of the narrow band filter 101, and the level of the signal is output. If the threshold value is equal to or higher than the threshold value th1 which is the detection level of the AC signal, the output 1
A comparison signal indicating true is output to c. Further, a level signal corresponding to a DC component is output to the output 1b of the average value detector 102. If this level signal is a value between a threshold value th2 and a threshold value th3 which is a detection level of the DC signal, a comparator ( 2) A comparison signal indicating true is output to the output 1d of 104. The determination circuit 105 outputs a true signal if both the output 1c of the comparator (1) 103 and the output 1c of the comparator (1) 103 are true. Threshold th1, threshold th2 and threshold th3
Are values determined by the magnitudes of the AC and DC components of the detected signal, respectively, and there is no direct relationship between the magnitudes of the two.

The operation of the signal detection circuit will be described in more detail with reference to the waveforms of each part shown in FIG.

FIG. 2A shows an input signal of the signal detection circuit. This signal may be considered to include the signal to be detected in the noise, or may be considered to be a baseband reception signal of a portable unit of a digital cordless telephone device described later. If it is a baseband reception signal of a portable unit, this signal includes a no-signal noise portion, a detected signal synchronization signal portion, a processing procedure, a voice signal, a data signal, a control signal, and an error correction code. And other signal parts other than the synchronization signal.

FIG. 2B shows the output 1a of the narrow band filter 101 with respect to the input signal shown in FIG. 2A. Since the narrow-band filter 101 is tuned to the frequency fc which is the AC component of the signal to be detected, the output signal 1a basically has the frequency fc.
Signal. The output level of the output signal 1a is
Due to the component of the frequency fc included in the noise of the input signal, even at a place other than the detected signal, for example, a threshold indicated by a dotted line as A1 in FIG. 2B corresponding to A0 in FIG.
A part of the AC waveform may exceed th1. Also, since the filter is a narrow band filter, Q is high, and the narrow band filter 1
01 is a constant response delay time with respect to the input signal.
Has td1. B0 and C in FIG. 2A of the detected signal
B of FIG. 2 (b) of the portion responding to 0, D0, E0, F0
1, C1, D1, E1, F1, and narrowband filter 101
Output 1a exceeds the threshold th1.

FIG. 2C shows an output 1c of the comparator (1) 103 corresponding to the output 1a of the narrow band filter 101.
The output 1c of the comparator (1) 103 is a narrow-band filter 101
2a correspond to B1, C1, D1, E1, and F1 in FIG. 2B in response to the detected signal in response to the detected signal, and correspond to B2, C2, D2, and E2 in FIG. , F2, but the output 1a of the narrow band-pass filter 101 exceeds the threshold th1 due to noise even in places other than the signal to be detected, and corresponds to A2 in FIG. The output is true at.

On the other hand, the input signal shown in FIG. 2A is also input to the average value detector 102. FIG. 2D shows the average value of the reception level corresponding to the output 1 b of the average value detector 102. The average value detector 102 also has a constant response delay time td2 with respect to the input signal, but this value is much smaller than the response delay time td1 of the narrow band filter 101.

When noise is input as an input signal to the average value detector 102, the temporal average value of the noise is a value near zero. Therefore, the output 1b of the average value detector 102
Becomes a value between the threshold value th2 and the threshold value th3, that is, the probability that the value is above the dotted line indicating the threshold value th3 and below the dotted line indicating the threshold value th2 in FIG. 2D is small.

The baseband reception signal of the portable unit of the digital cordless telephone device is a signal other than the synchronization signal,
That is, processing procedures, audio signals, data signals, control signals,
Even when a signal such as an error correction code is input, the average level of these signals is considered to be as low as possible.
02 output 1b rarely takes a value between the threshold value th2 and the threshold value th3. Further, the threshold value th2 and the threshold value th3 are set as described above. Therefore, the output 1b of the average value detector 102 indicating the average value of the reception level is the detected signal in FIG.
Only during the period from G0 to H0 in (a), the value is between the threshold th2 and the threshold th3 as in G3 to H3 in FIG. 2D.

With respect to the average value of the reception level as shown in FIG. 2D, the output 1d of the comparator (2) 104 becomes true only during the period when the input is a value between the threshold value th2 and the threshold value th3,
G4 to H4 become true as shown in FIG.

The output 1c of the comparator (1) 103 (FIG. 2)
(C)) and the output 1d of the comparator (2) 104 (FIG.
(E)) input to the determination circuit (AND gate) 105
Is true only during the period when both are true, and FIG.
It becomes true at B5, C5, D5, and E5 as shown in (f).

In this circuit, the response delay time td is applied to the output 1a of the narrow band filter 101 on the AC detection side as described above.
1, the duration of the detected signal is td1
Must be much longer than

FIG. 3 shows the block diagram shown in FIG. 1 as a digital circuit and a filter as an IIR (Infinit Impulse Resp.
FIG. 7 is a circuit diagram of a configuration example realized by an onse) filter.

In FIG. 3, reference numeral 51 denotes an adder, 52 denotes a unit delay element, 53 denotes a constant multiplier, 54 denotes a comparator, and 55 denotes an AND gate.

Using these elements, the narrow band filter 101 of FIG. 3 is configured as a second-order recursive IIR filter.

The average value detector 102 calculates the average value Pn of the present input signal level from the average value Pn-1 of the previous input signal level and the input signal level an sampled this time, by Pn = (Pn-1 + an) / 2. Is a cumulative addition and averaging circuit of the form obtained by

Further, the comparator 103 includes the narrow band filter 10
1 is a digital comparator that outputs true when the output exceeds a threshold th1, and a comparator 104 outputs a true when the output of the average detector 102 becomes a value between the thresholds th2 and th3. It is.

The judgment circuit 105 is an AND circuit that becomes true when the outputs of the comparators 103 and 104 are both true. Each of these circuits operates in synchronization with a clock for sampling a received signal.

As described above, when the digital filter is used, the variation in the elements is small and the whole apparatus can be made small as compared with the case where the analog elements are used.

FIG. 4 is a block diagram showing a portable cordless handset of a digital cordless telephone to which the present invention is applied, as an application example of the present invention. FIG. 5 is a block diagram of a demodulation unit of a modem unit of the portable cordless handset of the digital cordless telephone shown in FIG. 4, in which the signal detection circuit according to the embodiment of the present invention shown in FIG. ing.

In FIG. 4, reference numeral 1 denotes a receiving side which receives a radio wave from a base station, converts it into a digital baseband signal by performing an intermediate frequency process, and receives the radio wave from the base station. The radio unit 2 converts the frequency to power, amplifies the power, and transmits it to the base station as a radio wave. The receiving unit 2 performs frame synchronization and bit synchronization from the digital baseband signal, sends a synchronization signal to the control unit 7, and shifts the received signal by π / 4. A demodulation unit for performing QPSK demodulation is provided.
The modem unit having a modulator for K modulation, 3 is π on the receiving side.
The own slot signal is extracted from the digital signal demodulated by / 4 shift QPSK, and the transmitting side places a voice-encoded signal in its own slot of the TDMA signal in TDMA (Time).
DivisionMultiple Access), 4 is AD on the receiving side
PCM demodulation, a voice signal demodulated from a digital signal by PCM demodulation and sent to a speaker 5 as a receiver, and a voice signal from a microphone 6 as a transmitter is PCM-modulated on the transmitting side, and further, ADPCM-modulated. Department,
7, a control unit for controlling the entire apparatus; 71, a memory unit for storing information necessary for control, programs, abbreviated dials, and the like; 72, an operation unit for performing device operations necessary for communication including key dial operation; A sounder 73 generates a ringing tone.

The radio section 1 is used in common for transmission and reception. The antenna 11 transmits and receives radio waves, and receives a radio reception signal from the base station received by the antenna 11 via the transmission / reception switch 15 to tune and select a station. A receiving unit 12 for converting a radio reception signal into an intermediate frequency signal with a carrier signal or the like output from a synthesizer 14 and converting the signal into a digital baseband signal; a π / 4 shift QPSK modulation signal from a modulation unit 22; A transmitting unit 13 that modulates with a carrier signal output from a synthesizer 14 and amplifies the power to a level necessary for transmission, a synthesizer 14 that synthesizes and outputs a carrier signal from an oscillation signal from a crystal oscillator 16, and transmits and receives from a control unit 7. A transmission / reception switch 15 for switching the antenna 11 between the reception unit 12 and the transmission unit 13 according to a control signal
Etc.

The modem section 2 demodulates and detects a π / 4-shifted QPSK modulated signal of the received digital baseband signal output from the receiving section 12 and converts it into a serial data signal.
And the serial data signal from the TDMA transmission unit 32
It is composed of a modulating unit 22 for modulating a / 4 shift QPSK modulated signal.

The TDMA section 3 is provided with a TDMA receiving section 31 for performing time division multiplexing decoding for extracting its own slot signal from the serial data signal output from the demodulating section 21 and an ADPCM.
It comprises a TDMA transmission unit 32 that encodes an audio signal from the codec 41 into a transmission slot.

The speech unit 4 uses an adaptive differential pulse code modulation code combining apparatus that performs voice coding with simple processing and small delay while maintaining voice quality in accordance with linear prediction of voice signals by utilizing voice signal redundancy. ADPCM (Adapti
ve Pulse Code Modulation) codec 41 and a PCM that digitizes analog voice into PCM code and converts voice digitized into PCM code into an analog signal
(Pulse Code Modulation) A codec 42 is connected to a speaker 5 as a receiver and a microphone 6 as a transmitter.

On the other hand, the control section 7 is constituted by a microprocessor or the like, and controls the entire apparatus. The control unit 7 is connected to an operation unit 72 for performing device operations such as a key dial operation, a sounder 73 for generating a ringing tone, and a memory unit 71 for storing information necessary for control, programs, speed dials, and the like. .

FIG. 5 is a block diagram of the demodulation unit 21 of the modem unit 2. The demodulation unit 21 includes a delay detection circuit 211, an original oscillator 212, a frequency division circuit 213, a phase control circuit 214, a signal identification circuit 215, and a signal detection circuit 216.

The reception signal from the antenna 11 is demodulated by the reception unit 12 of the radio unit 1 and the delay detection circuit 21 of the demodulation unit 21
1 and output as a digital signal through a signal identification circuit 215. As the synchronization signal of the signal identification circuit 215, a signal obtained by dividing the oscillation output from the original oscillator 212 by the frequency divider 213 and synchronizing with the synchronization burst signal of the received signal by the phase control circuit 214 is used. The signal detection circuit 216 detects the synchronization burst signal from the output of the delay detection circuit 211 and outputs an output for adjusting the phase of the synchronization signal. The signal detection circuit 216 is the signal detection circuit shown in FIG.
Are respectively input.

In the present invention, since the AC frequency component of the signal to be detected and the average value of the signal to be detected are simultaneously observed and the signal to be detected is detected only when both satisfy the specified value, erroneous detection due to noise is reduced. . Therefore, the order of the filters can be reduced, and in the case of a digital filter, the function can be sufficiently satisfied even with a second-order IIR filter as shown in FIG. 3, and the circuit scale can be sufficiently reduced.

[0047]

As described above, according to the present invention, a signal detection circuit for detecting a signal having a specific frequency component and a direct current component is used to output a narrow band filter tuned to a specific frequency component and an output of the narrow band filter. The first to compare with the first threshold
, An average value detection circuit that extracts the average value of the input signal, and a second comparison circuit that compares the output of the average value detection circuit with two high and low second and third thresholds. When the output of the narrow band filter from the output of the first comparison circuit exceeds the first threshold value and the output of the average value detection circuit from the output of the second comparison circuit is between the second and third threshold values, the signal is determined. Is determined to be detected. As a result, the signal detection accuracy can be improved, the order of the filter can be reduced, and the circuit scale can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram of a signal detection circuit according to an embodiment of the present invention.

FIG. 2 is a waveform chart of each part of the embodiment shown in FIG. 1;

FIG. 3 is a circuit diagram of a configuration example in which the embodiment shown in FIG. 1 is realized by an IIR filter.

FIG. 4 is a block diagram of a digital cordless telephone portable handset to which the present invention is applied.

FIG. 5 is a block diagram of a demodulation unit of the digital cordless telephone portable handset shown in FIG. 4;

FIG. 6 is a block diagram of a conventional signal detection circuit.

FIG. 7 is a waveform chart showing an example of a frequency response and a time response of a narrow band filter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Radio part 2 Modem part 3 TDMA part 4 Talk part 5 Receiver (speaker) 6 Transmitter (microphone) 7 Control part 11 Antenna 12 Receiving part 13 Transmitting part 14 Synthesizer 15 Transmission / reception switch 16 Radio frequency oscillator 21 Demodulation part 22 Modulation Unit 31 TDMA reception unit 32 TDMA transmission unit 32 41 ADPCM codec 42 PCM codec 51 adder 52 unit delay element 53 constant multiplier 54 comparator 55 AND gate 71 memory unit 72 operation unit 73 sounder 101 narrow band filter 102 average value detector 103, 104 Comparator 105 Judgment circuit 211 Delay detection circuit 212 Original oscillator 213 Divider circuit 214 Phase control circuit 215 Signal identification circuit 216 Signal detection circuit

Claims (3)

[Claims] 1. A signal detection circuit for detecting a detected signal from an input signal including a detected signal having a specific frequency component superimposed on a DC component, a narrow band filter tuned to the specific frequency component, A first comparing the output of the narrow band filter with a first threshold;
An average value detection circuit that extracts an average value of the input signal; a second comparison circuit that compares an output of the average value detection circuit with two high and low second and third threshold values; A signal detection circuit comprising: a determination circuit that determines the detection of the detected signal from an output of the first comparison circuit and an output of the second comparison circuit. 2. The signal detection circuit according to claim 1, wherein said narrow-band filter comprises a digital filter. 3. The signal detection circuit according to claim 2, wherein said digital filter comprises a second-order infinite impulse response filter.