JP3588175B2 - Waveform identification circuit - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a waveform identification circuit for identifying whether or not the waveforms of two input signals are the same, and more particularly, to the same program such as an FM radio receiver having an RDS (radio data system) function. The present invention relates to a waveform identical identification circuit suitable for use as identification means.
[0002]
[Prior art]
The FM receiver with RDS function automatically selects another station broadcasting the same program and continuously receives it even if the reception sensitivity is lowered while the vehicle is running or the vehicle goes out of the broadcasting area. Is provided. The present applicant has previously described, as one method for realizing such a function, a demodulated waveform of a received signal of a broadcast program of a broadcast station currently being received and a broadcast program of another broadcast station which has been switched and received. Japanese Patent Laid-Open No. Sho 60-224318 has proposed an automatic radio for the same program which distinguishes whether two stations are broadcasting the same program by comparing demodulated waveforms of received signals.
[0003]
FIG. 3 is a diagram showing the principle configuration of a waveform identical identification circuit portion employed in the same program automatic identification radio according to the prior application.
In the figure, reference numeral 1 denotes an antenna, 2 is a mixer to obtain an intermediate frequency (IF), 3 ₁ is a first VCO as a local oscillator that varies its oscillation frequency by an applied voltage (voltage controlled oscillator). The first VCO 3 ₁ includes a broadcast station being received (hereinafter, referred to as current station) is a local oscillator for tuning to. Broadcast waves received by an antenna 1 is sent to the mixer 2 is converted into a predetermined intermediate frequency is mixed with incoming local oscillation signal sent from the VCO 3 _1, it is sent to the detection circuit 4. The demodulated signal demodulated by the detection circuit 4 is sent to a multiplex circuit (MPX) 5, separated into left and right stereo signals L and R, and output as an audio signal. The above configuration is a configuration of a known FM radio receiver.
[0004]
In the FM radio receiver having such a configuration, the waveform identification determination circuit prior application, first VCO 3 ₁ other broadcasting stations which are broadcasting the same broadcast program (hereinafter, referred to as alternative station) for tuning to a a VCO 3 ₂ is a second local oscillator, a provided with change-over switch 6 for switching between VCO 3 ₁ of the the second VCO ₂ with the first, to prevent aliasing noise by sampling the output of the detector circuit 4 Is connected to the low-pass filter (LPF) 7, and two sample-and-hold circuits 8, 9 are connected to the output terminal of the LPF 7.
[0005]
Output terminals of the sample-and-hold circuits 8 and 9 are connected to binarization circuits 10 and 11 for converting respective sample values into binary signals of “1” and “0”. The determination circuit 12 compares the binary signals output from the conversion circuits 10 and 11 to determine whether the demodulated waveforms of the current station and the substitute station are the same.
[0006]
The control unit 13 generates a first sampling pulse A for sampling a demodulated signal of the current station currently being received and a second sampling pulse B for sampling a demodulated signal of the substitute station, and performs switching. A switching control signal for switching the switch 6 is output. The pass band of the LPF 7 is set so as to pass only a frequency band equal to or less than half the sampling frequency of the sampling pulses A and B.
[0007]
The operation of the waveform identical identification circuit of the prior application having the above configuration will be described with reference to a time chart of FIG. Incidentally, _{V 1} a control voltage applied to the VCO 3 ₁ when receiving the current station reception frequency _{f 1,} and _{V 2} the control voltage applied to the VCO 3 ₂ when receiving alternative station receiving frequency _{f 2} I do. Also, the demodulation output of the detection circuit 4 when receiving the current station of the reception frequency f ₁ is F ₁ (see FIG. 4A), and the detection circuit when receiving the alternative station of the reception frequency f _2. The demodulated output of No. 4 is F ₂ (see FIG. 4B).
[0008]
When the reception state is good normal reception of the current station, the change-over switch 6 is set to VCO 3 ₁ side to receive the current station reception frequency f _1. The waveform identical identification circuit is configured to listen to the current station while listening to the current station in order to make it possible to smoothly switch to another broadcast station that is broadcasting the same program when the reception condition of the current station deteriorates. The following program identification operation is performed for each time.
[0009]
That is, the control unit 13 generates a first sampling pulse A having a predetermined sampling period and a second sampling pulse B having a predetermined sampling period as shown in FIG. The second sampling pulse B is sent to the sample-and-hold circuit 8 and the second sample-and-hold circuit 9 is sent. Further, it sends the VCO 3 ₁ and VCO 3 ₂ switch control signal to the change-over switch 6.
[0010]
First sample-and-hold circuit 8 which receives the first sampling pulse A samples the demodulated output F ₁ of the current station in the received holding the (FIG. 4 (d)), binarization Send to circuit 10. The binarization circuit 10 compares this sampling signal with a predetermined reference voltage V _ref (for example, V _ref = 0 V) and converts it into a binary signal of “1” and “0” as shown in FIG. Then, it is sent to the judgment circuit 12.
[0011]
Further, the changeover switch 6 which has received the switching control signal from the control unit 13 switches the local oscillator from VCO 3 ₁ to VCO 3 _2, switch to an alternate station receiving station from the current station. Second sampling pulse B, the oscillation frequency of the switched VCO 3 ₂ is generated in a stable point, it is transmitted from the control unit 13 to the second sample-and-hold circuit 9.
[0012]
Second sample-and-hold circuit 9 which receives the second sampling pulse B samples the demodulated output F ₂ alternative station holds it (FIG. 4 (f)), the binarizing circuit 11 send. The binarization circuit 11 compares this sampling signal with a predetermined reference voltage V _ref (for example, V _ref = 0 V) and converts it into a binary signal of “1” and “0” as shown in FIG. Then, it is sent to the judgment circuit 12.
[0013]
As shown in FIG. 4 (h), after a predetermined time has elapsed from the transmission of the sampling pulses A and B, the determination circuit 12 outputs "1" of the two binary signals transmitted from the binarization circuits 10 and 11. A match / mismatch of the signs of “0” is detected, and when the signs match, an output “1” is generated, and when the signs do not match, an output “0” is generated. Count the number of codes of 0 ". When the number of “1” is equal to or more than the predetermined number, it is determined that the current station and the substitute station have the same waveform, that is, the current station and the substitute station are broadcasting the same program.
[0014]
For example, in the case of the example of FIG. 4H, the number of “1” is two and the number of “0” is four at a predetermined determination time, and the number of “0” is larger. No, that is, not the same program.
[0015]
The waveform identical identification circuit of the prior application identifies whether two broadcasting stations are currently broadcasting the same program, and if the same program is the same program, the reception status of the current station becomes poor. Is switched to an alternative station that broadcasts the same program.
[0016]
As shown in FIG. 5, the changeover switch 6 can be switched to the VCO ₂ only during a very short period of time such that noise when switching to the alternative station does not sound from the speaker. This is because it is necessary to prevent the current station from listening by being switched to the alternative station by the same program identification processing.
[0017]
Further, in FIG. 4, VOC3 _{1, 3 2} shown surrounded by a broken line, the change-over switch 6, a local oscillator circuit portion comprising the control voltage _V 1, _{V 2,} in the actual receiver consists of a frequency synthesizer using a PLL Have been.
[0018]
[Problems to be solved by the invention]
Incidentally, VCO 3 _{1, 3 2} constituting the local oscillation circuit, the oscillation frequency is determined by the applied voltage _V 1, _{V 2.} Accordingly, there is no problem if the applied voltages V ₁ and V ₂ are controlled with high precision and completely match the specified values. However, if the applied voltages V ₁ and V ₂ deviate from the specified values, the oscillation frequencies of the VCOs _{3 1} and VCO 3 ₂ are also reduced. The center frequency of the intermediate frequency signal output from the mixer 2 also shifts by that amount.
[0019]
On the other hand, the detector 4 of the FM receiver detects and demodulates the intermediate frequency signal by the so-called S-shaped characteristic shown in FIG. Therefore, it varies the oscillation frequency of the VCO 3 ₁ or VCO 3 _2, if the center frequency of the intermediate frequency signal output from the mixer 2 is shifted, as shown in FIG. 6, the demodulated output according to the deviation Δf The average value shifts by ΔE, and a DC offset occurs. As a result, the demodulated output F ₁ or F ₂ are outputted from the detection circuit 4, where should the amplitude signal which varies about a zero level as would otherwise FIG. 7 (a), the example of FIG. 7 (c) Thus, the average value is reduced by the DC offset voltage ΔE.
[0020]
When the average value of the demodulated output changes in this way, even if it is binarized, it is converted into a binary signal completely different from the original binary signal when there is no DC offset. For example, when the original demodulated output without the DC offset shown in FIG. 7A is binarized, a binary signal as shown in FIG. 7B is obtained. For example, as shown in FIG. When the demodulation output is lower than the 0 level due to the DC offset, the output of the binary signal becomes “0” in all sections as shown in FIG. For this reason, there is a problem that accurate determination cannot be performed if there is a DC offset in the demodulated output.
[0021]
SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem. It is an object of the present invention to automatically cancel a DC offset of an input signal to be compared with a waveform and always perform accurate waveform identity determination. It is an object of the present invention to provide a circuit for identifying the same waveform.
[0022]
[Means for Solving the Problems]
In order to solve the above problems, the present invention employs the following means.
That is, according to the first aspect of the present invention, a plurality of waveforms to be compared by selecting and applying a control voltage prepared in advance to a single local oscillation circuit composed of a voltage controlled oscillator composed of a frequency synthesizer using a PLL. The input signal is switched and selected and input, and the selected input signal is sampled and the respective waveforms are compared to identify the same waveform of the input signal. Sampling means for sampling and outputting each input signal at a predetermined cycle, an offset voltage extracting means for extracting a DC offset voltage included in a sampling signal of each input signal output from the sampling means, The DC offset voltage for each input signal extracted by the means is compared with a reference voltage for binarization. And binarizing means for binarizing the sampling signal of each input signal output from the sampling means, and comparing the binary signal of each input signal output from the binarizing means. And determination means for determining whether or not the waveforms are the same.
[0023]
In the case of such a configuration, the binarizing unit binarizes each input signal using the DC offset voltage included in each input signal extracted by the DC offset extracting unit as a reference voltage. Therefore, even when a DC offset is included in the input signal, the DC offset is automatically canceled, and each input signal can be accurately binarized.
[0024]
According to a second aspect of the present invention, in the first aspect of the present invention, the offset voltage extracting means includes a rectifier circuit.
[0025]
With such a configuration, the circuit can be most simply configured.
[0026]
Further, according to a third aspect of the present invention, in the first or second aspect, the input signal is a demodulated signal of a radio broadcast.
[0027]
With such a configuration, it is possible to extremely accurately determine whether broadcast programs match or not in an FM receiver or the like having an RDS function.
[0028]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows an example of a waveform identical identification circuit according to the present invention, which is an example applied to an FM radio receiver. The same parts as those of the previously-identified waveform identical identification circuit (FIG. 3) are denoted by the same reference numerals, and detailed description thereof will be omitted.
[0029]
The waveform identical identification circuit according to the present invention has a circuit configuration similar to that of the prior application, in which offset extraction circuits 14 and 15 are respectively connected to the output terminals of the sample-and-hold circuits 8 and 9, and a first offset extraction circuit The DC offset voltage of the demodulated output of the current station extracted at 14 is used as a reference voltage of the first binarization circuit 10, and the DC offset voltage of the demodulated output of the substitute station extracted at the second offset extracting circuit 14 is used. Is used as a reference voltage of the second binarization circuit 11.
[0030]
As the offset extracting circuits 14 and 15, a known rectifier circuit may be used most simply.
[0031]
In the example of FIG. 1, one VCO 3 is used as a local oscillator and the control voltages V ₁ and V ₂ applied to the VCO ₃ are switched by the changeover switch 6 in order to make the circuit as small as possible. It is configured to switch and receive an alternative station.
[0032]
Further, the local oscillation circuit portion including the VOC 3, the changeover switch 6, and the control voltages V ₁ and V ₂ shown by a broken line is constituted by a frequency synthesizer using a PLL in an actual receiver.
[0033]
The operation of the same-waveform identification circuit having the above configuration will be described with reference to the waveform diagram of FIG.
Since the operations up to the sample and hold circuits 8 and 9 are the same as those in FIG. 3, only the circuit operations after the sample and hold circuits 8 and 9 will be described. Furthermore, in the following description, the current station and alternate station has broadcast the same program, the DC offset as the demodulated output F ₂ of the current station are shown in FIGS. 2 (a) that is output from the detection circuit 4 0 , and the other hand, it is assumed that the demodulated output F ₂ of the alternative station has a DC offset -ΔE as shown in Figure 2 (c).
[0034]
Now, the first sample-and-hold circuit 8 which receives the first sampling pulse A holds this by sampling the demodulated output F ₁ of the current station currently being received as shown in FIG. 2 (a), the The signals are sent to the + terminal of the first binarization circuit 10 and the input terminal of the first offset extraction circuit 14, respectively.
[0035]
Further, the second sample-and-hold circuit 9 receiving the second sampling pulse B samples and holds the demodulated output F ₂ −ΔE of the alternative station shown in FIG. To the + terminal of the binarization circuit 11 and the input terminal of the second offset extraction circuit 14.
[0036]
First offset extracting circuit 14, the sampling signal of the demodulated output F ₁ of the current station shown in sent from the first sample-and-hold circuit 8 FIGS. 2 (a) rectified, the DC voltage component Extract as offset voltage. For example of FIG. 2 (a), since the DC offset in the demodulated output F ₁ of the current station has not occurred, the extracted DC offset voltage becomes 0V.
[0037]
Therefore, the DC offset voltage 0 V is input to the negative terminal of the first binarization circuit 10 as a reference voltage for binarization. As a result, the first binarizing circuit 10 binarizes the sampling signal input to the + terminal using the DC offset voltage 0 V as a reference voltage. ).
[0038]
On the other hand, the second offset extraction circuit 15 rectifies the sampling signal of the demodulated output F ₂ −ΔE of the alternative station shown in FIG. 2C sent from the second sample-and-hold circuit 9, The DC voltage component is extracted as an offset voltage. In the example of FIG. 2C, since a DC offset −ΔE has occurred in the demodulated output of the substitute station, the extracted DC offset voltage is −ΔE.
[0039]
Therefore, this DC offset voltage −ΔE is input to the − terminal of the second binarization circuit 11 as a reference voltage for binarization. As a result, the second binarization circuit 11 binarizes the sampling signal input to the + terminal using the DC offset voltage −ΔE as a reference voltage, so that the converted binary signal is shown in FIG. The waveform becomes as shown in d).
[0040]
As apparent from comparison of FIGS. 2B and 2D, the binary signal output from the second binary circuit 11 has a DC offset −ΔE in the demodulated output. Instead, it is correctly converted into the same binary signal as in FIG.
[0041]
The determination circuit 12 determines whether or not the signs of the binary signals “1” and “0” sent from the first and second binarization circuits 10 and 11 match or disagree with each other, similarly to the waveform identification circuit of the prior application. To determine whether the current station and the substitute station are broadcasting the same program (see FIGS. 4E, 4G, and 4H).
[0042]
In this manner, the DC offset voltages extracted by the offset extraction circuits 14 and 15 are used as the reference voltages of the binarization circuits 10 and 11, and the sampling signals input to the respective circuits are binarized. Even when a DC offset occurs in the received demodulated output, it is possible to accurately determine the same waveform.
[0043]
Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications can be made in accordance with the gist of the present invention.
[0044]
【The invention's effect】
According to the first aspect of the invention, sampling means for sampling and outputting each selected input signal at a predetermined cycle, and a DC offset voltage included in a sampling signal of each input signal output from the sampling means. The offset voltage extracting means to be extracted, and the DC offset voltage of each input signal extracted by the offset voltage extracting means is used as a reference voltage for binarization, and a sampling signal of each input signal output from the sampling means is used. It is provided with a binarizing means for binarizing, and a judging means for judging whether or not both waveforms are the same by comparing a binary signal of each input signal outputted from the binarizing means. Therefore, even if a DC offset occurs in the input signal to be compared, it can be automatically canceled. You can always perform accurate waveform match determination.
[0045]
Further, according to the second aspect of the present invention, since the offset voltage extracting means is constituted by a rectifier circuit, the circuit can be configured simply and simply, and the cost can be reduced.
[0046]
Furthermore, according to the third aspect of the present invention, since a demodulated signal of a radio broadcast is input as the input signal, it is possible to extremely accurately identify coincidence / non-coincidence of broadcast programs in an FM receiver having an RDS function. Can be performed.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an example of a waveform identical identification circuit according to the present invention.
FIG. 2 is a waveform chart for explaining the operation of the circuit of FIG. 1;
FIG. 3 is a principle configuration diagram of a waveform identical identification circuit of the prior application.
FIG. 4 is a time chart of the circuit of FIG. 3;
FIG. 5 is an explanatory diagram of a waveform when a demodulation output is switched.
FIG. 6 is a diagram illustrating detection characteristics of an FM receiver.
FIG. 7 is a diagram illustrating an operation when a DC offset occurs in a demodulated output.
[Explanation of symbols]
1 antenna 2 mixer 3 VCO
4 Detection circuit 5 Multiplex circuit (MPX)
6 Changeover switch 7 Low pass filter (LPF)
8, 9 Sample and hold circuit 10, 11 Binarization circuit 12 Judgment circuit 13 Control unit 14, 15 Offset extraction circuit F ₁ Demodulated output of current station (input signal)
Demodulated output of the F ₂ Alternate station (input signal)
A, B Sampling pulse ΔE DC offset voltage

Claims (3)

By selecting and applying a control voltage prepared in advance to a single local oscillation circuit consisting of a voltage controlled oscillator composed of a frequency synthesizer using a PLL, a plurality of input signals to be compared for waveforms are selected and input. A waveform identification circuit that samples the selected input signal and compares the waveforms to identify the waveform of the input signal.
Sampling means for sampling and outputting each of the selected input signals at a predetermined cycle,
Offset voltage extracting means for extracting a DC offset voltage included in the sampling signal of each input signal output from the sampling means,
Binarization means for using the DC offset voltage of each input signal extracted by the offset voltage extraction means as a reference voltage for binarization and binarizing a sampling signal of each input signal output from the sampling means When,
Determining means for comparing whether the waveforms of the two input signals are the same by comparing the binary signals of the respective input signals output from the binarizing means,
A waveform identification circuit comprising: 2. A circuit according to claim 1, wherein said offset voltage extracting means comprises a rectifier circuit. The invention according to claim 3 is the circuit according to claim 1 or 2, wherein the input signal is a demodulated signal of a radio broadcast.

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