JPH0129341B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for detecting a frequency modulated signal using a binary digital signal, and particularly to a detection device suitable for integration into an integrated circuit.

A so-called direct conversion method is known as a method for realizing a frequency detection device using an integrated circuit. This method has the advantage that filtering and other processing can be performed at the baseband because the frequency of the received wave is directly converted to the baseband. Conventionally known baseband signal processing methods using differentiation and multiplication have the advantage of being able to process signals modulated with analog signals, but on the other hand, they require automatic gain adjustment and circuit balance. The drawback was that it was quite difficult to implement.

SUMMARY OF THE INVENTION An object of the present invention is to provide a detection device for a frequency modulated wave modulated by a binary digital signal, which eliminates such drawbacks and can be easily implemented using an integrated circuit.

According to the present invention, an input signal to be detected frequency-modulated by a binary digital signal is separated into 2N (here, N is a positive integer) signals, which are approximately equal to the center frequency of the input modulated wave. By isolating the output of the local oscillator with the frequency
2N local oscillation signals corresponding to 2N input signals are generated, 2N different phase differences are given between the 2N input signals and the 2N local oscillation signals corresponding thereto, and the 2N input signals
2N baseband signals with different phases are created by converting the frequency to baseband using 2 local oscillation signals, and each of the resulting signals is binarized into 2N baseband signals. A first signal is created by creating a binary signal and taking the exclusive OR of these signals, and the 2N baseband signals are arranged in an order in which their phases are modulo 180°. When arranged, the entire binarized signals corresponding to every other signal obtained from these signals are defined as a first signal group, and the entire remaining binarized signal groups are defined as a second signal group. When the state of any signal in the first signal group changes, the state of the binary signal selects one of the two, and each time the state of any signal in the second signal group changes. A reference signal generated by selecting the other state of the binary signal is used as a second signal, an exclusive OR signal of the second signal and the first signal is created, and a signal obtained from this signal is obtained. The above object can be achieved by using the detected signal as the detection output.

A detailed explanation will be given below using the drawings. FIG. 1 is a block diagram showing a first embodiment of the present invention.
When the received wave frequency-modulated with a mark or space binary digital signal is input to the input terminal 1, the output of the local oscillator 3 having an oscillation frequency approximately equal to the center frequency is divided into two, and the phase shifter 4 divides the output into two.
The signal obtained by giving a phase shift difference of 90° between the two signals divided by is used as a local oscillation signal, and mixer 2
1 and 22, the frequency is converted to baseband. The low-pass filters 51 and 52 extract only the baseband signal and limit the noise band. The baseband signals are input to binarization circuits 61 and 62, respectively, and the binarized signals I,
Q is obtained. The phase difference between the input modulation signal and the local oscillation signal is determined in mixer 21 and mixer 22.
Due to the 90° difference, the phase difference between signal I and signal Q will also be 90°. This signal waveform is, for example,
The result is as shown in FIG. Here, a solid line indicates a modulated signal mark, and a broken line indicates a space. By inputting the signals I and Q to the exclusive OR circuit 71, the signal IQ as shown in FIG.
is obtained. Parts of the signals I and Q are input to a reference signal generation circuit 80, and as will be explained later, the period is equal to that of the signal IQ, and the relative phase with respect to the signal I or Q is such that the modulating signal is a mark or a space. An unchanging reference signal Z is thus generated. The reference signal Z is input to the exclusive OR circuit 72 together with the signal IQ. The output signal X becomes a mark or space signal which is a modulation signal, indicating that frequency detection is performed.

Here, the operation of the reference signal generation circuit 80 surrounded by the broken line in FIG. 1 will be explained. Signals I and Q are input to differential folding circuits 81 and 82, respectively, and if the input shown in FIG. 3a is applied, for example,
As shown in Figure b, a pulse is generated at a signal change point. Therefore, the reset flip-flop circuit 9 is set at the rising and falling edges of the signal Q, and is set at the rising and falling edges of the signal I, so that its output signal Z is equal to the repetition period of the signal IQ. ,and,
Due to the function of the differential folding circuit, the relative phase does not change depending on whether the modulated signal is a mark or a space. For example, the differential folding circuit is
As shown in the figure, this can be realized by a circuit configuration in which an input signal and a signal obtained by inputting this to the delay circuit 5 are input to the exclusive OR circuit 7.

In the embodiment described here, the phase difference between the signals I and Q is not limited to 90 degrees, but can be any value other than zero, which can be easily seen by drawing a waveform diagram like the one shown in Figure 4. It can be understood. Furthermore, signals I,Q
Instead of providing a phase difference between the local oscillation signals as in the example shown here, a method of providing a phase difference between the modulation signals input to the two mixers is also possible. good. Further, the input signals I and Q to the set terminal and reset terminal of the set/reset flip-flop circuit 9 may be interchanged. No matter which of these combinations is selected, either a mark or space signal can be obtained correctly, or only a detected signal in which these signals have been exchanged will be obtained. In the latter case, a circuit for inverting data may be added.

A second embodiment of the invention is shown in FIG. The frequency modulation signal input to the input terminal 1 is obtained by applying relative phase differences of 0°, 45°, 90°, and 135° to the output signal of the local oscillator 3, which has an oscillation frequency approximately equal to its center frequency. The four signals are frequency-converted to baseband by mixers 21, 22, 23, and 24, each of which serves as a local oscillation signal. After passing these signals through low-pass filters 51, 52, 53, and 54, the signals obtained by passing through binarization circuits 61, 62, 63, and 64 are converted into Q ₂ , I ₂ , Q ₁ , I ₁ Let's say.
These signal waveforms have different phases, for example, as shown in FIG. here,
A solid line indicates a case where the modulation signal is a mark, and a broken line indicates a case where the modulation signal is a space. The signals I ₁ , Q ₁ , I ₂ , and Q ₂ are input to the exclusive OR circuit 71, and the output signal IQ is as shown in FIG. The signal IQ is the signal I ₁ ,
Reference signal generation circuit 80 with Q ₁ , I ₂ , and Q ₂ as inputs
The detection output signal X is input together with the reference signal Z generated by the exclusive OR circuit 72 to obtain the detection output signal X (see FIG. 7).

The reference signal generation circuit can be realized, for example, by a circuit as shown in FIG. The operation of this circuit is almost self-evident and will not be explained in detail, but in short, exclusive OR circuits 71, 73 and delay circuit 51 generate pulses at the rising and falling points of signals I ₂ and Q ₂ . The reset circuit 9 is set by the pulse, and the exclusive OR circuits 72 and 73 and the delay circuit 52
A pulse is generated at the rising and falling points of the signals _I1 and _Q1 , and the set-reset circuit 9 is set by this pulse. The reason why the relative phase of the output signal Z of this circuit does not depend on whether the modulated signal is a mark or a space is because the first
This is due to the function of a differential folding circuit composed of delay circuits 51 and 52 and exclusive OR circuits 73 and 74, as in the embodiment. Also, the period,
It is obvious that it is equal to the period of signal IQ.

Although the second embodiment has a more complex configuration than the first embodiment, it has the advantage that it can be applied to modulated waves with small phase changes, that is, modulated waves with smaller modulation indexes.

As can be inferred from the operations of the first and second embodiments, the same operation can be performed even if the number of local oscillation signals is increased to 2N and the number of baseband signals is increased correspondingly. Further, in this embodiment, the case where the phases of the baseband signals are arranged at equal intervals has been described, but it can be easily confirmed that the same operation can be performed even when the intervals are not equal. In this case, what is required in order to generate the reference signal, as can be inferred from the operation shown above, is to arrange the baseband signals in an order modulo 180° in the phase plane, and to sequentially convert these signals into 1 A flip-flop is set at the rising and falling points of one of the binary signals corresponding to the one taken every other baseband signal, and one of the binary signals corresponding to the remaining baseband signals taken in order is set. All it does is operate to reset the flip-flop at the rising and falling points of the signal.

As explained above, all the circuits after the mixer operate at the baseband, and all the circuits after the binarization circuit can be configured with digital circuits, so the present invention has the effect of facilitating implementation with integrated circuits. . Further, the baseband circuit and subsequent circuits can also be realized by once converting into digital values and then using a microprocessor or the like to perform signal processing according to the method shown in the present invention.

In describing the operation of embodiments of the invention, it has been assumed that all circuits operate ideally. In an actual circuit, impulse-like noise may occur in the detection output, which is the output of the exclusive OR circuit, due to delays or the like. In this case, the influence can be removed by passing the detection output through a low-pass filter. Also, here, two separate exclusive OR circuits were used to create the signal IQ and to obtain the detection signal, but these are
It is obvious that they can be combined into one.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention, FIG. 2 is a block diagram showing a differential folding circuit, and FIG. 3 is a waveform diagram explaining the operation of the differential folding circuit. FIG. 4 is a waveform diagram for explaining the operation of the first embodiment, FIG. 5 is a block diagram showing the second embodiment of the present invention, and FIG. 6 is a reference signal generation circuit in the second embodiment. A block diagram showing an example of
FIG. 7 is a waveform diagram for explaining the operation of the second embodiment. In these figures, 1 is a frequency modulated wave input terminal, 2 is an output terminal, 21, 22, 2
3, 24 are mixers, 3 is a local oscillator, 4 is a phase shifter, 51, 52, 53, 54 are low-pass filters, 61, 62, 63, 64 are binarization circuits, 7
1, 72, 73, 74 are exclusive OR circuits, 80
8 is a reference signal generation circuit, 81 and 82 are differential folding circuits, and 9 is a reset flip-flop circuit.

Claims (1)

[Claims] 1. A local oscillator that branches an input signal to be detected frequency-modulated by a binary digital signal into 2N (here, N is a positive integer) signals and has a frequency approximately equal to the center frequency of the input modulated wave. 2N local oscillation signals corresponding to the 2N input signals are created by branching the outputs of the 2N local oscillation signals, and between the 2N input signals and the 2N local oscillation signals corresponding to the 2N input signals, Give 2N different phase differences,
By frequency converting the 2N input signals to baseband by the 2N local oscillation signals, 2N baseband signals having different phases are created, and each of the resulting signals is By creating 2N binarized signals obtained by binarizing and taking the exclusive OR of these signals, the first
, and when the 2N baseband signals are arranged in an order in which their phases are modulo 180°, the binarization corresponding to the signal obtained by sequentially taking every other signal. When the entire signal is defined as a first signal group and the entire remaining binarized signal group is defined as a second signal group, each time the state of any signal in the first signal group changes, a binary signal is generated. A reference signal generated by selecting one of the signal states and selecting the other state of the binary signal each time the state of any signal of the second signal group changes is used as a second signal. A frequency detection device characterized in that: an exclusive OR signal of the second signal and the first signal is generated, and a signal obtained from this signal is used as a detection output signal.