JPH0626347B2 - FSK signal receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention is used as a receiver of digital signals in the field of telecommunications or optical communications. The present invention is based on FSK (Frequenc
y Shit Keying (binary frequency modulation) signal demodulation circuit. In particular, it relates to an FSK signal receiver for directly demodulating an FSK signal into a baseband signal.

[Conventional technology]

FIG. 9 is a block diagram of a conventional FSK signal receiver. In this conventional receiver, one reception FSK signal received by an antenna 1 is amplified to a predetermined level by a high-frequency amplifier 2, branched, and given to a pair of mixing circuits 5 and 6, and the mixing circuits 5 and 6 are combined. A local oscillation signal having a frequency substantially equal to the carrier frequency of the FSK signal is applied from the local oscillation circuit 3 to the local oscillation signal applied to the pair of mixing circuits by π / 2.
Is provided with a phase shift circuit 4 for providing a considerable phase difference, and a pair of low-pass filters 7 and 8 through which the FSK demodulated signal waves of the output signals of the mixing circuits 5 and 6 pass, respectively. The output signals of the low-pass filters 7 and 8 are supplied to the comparison circuit 13 via the low-frequency amplifiers 9 and 10 and the amplitude limiting circuits 11 and 12 that limit the output signals to a constant amplitude. By comparing the two signals at 13, FS
This is a device for demodulating a K signal.

Compared with the conventional super-heterodyne system, this device does not require an amplifier or a filter in the intermediate frequency band, and is receiving attention as a device that can be miniaturized and integrated into an integrated circuit.

The operation of this device will be briefly described. Assuming that the carrier frequency of the received FSK signal is _c and the frequency displacement of the binary FSK signal is δ, the local oscillation frequency _L is made equal to the carrier frequency _c , so that the output of the mixing circuit 6 has a signal of its fundamental frequency. As a result, a baseband signal equal to the frequency displacement δ is obtained. The low-pass filters 7 and 8 extract the signal of the fundamental frequency. Here, when a phase difference of π / 2 is given to the local oscillation signals input to the two mixing circuits 5 and 6, the output signal of the fundamental frequency of one mixing circuit is a (t) cos (2πδt). Then, the output signal of the fundamental frequency of the other mixing circuit becomes a (t) cos (2πδt + π / 2) = -a (t) sin (2πδt), and the output of the two low-pass filters 7 and 8 is Signals having a phase difference of π / 2 are obtained. Where a (t)
Is the input voltage of the receiver, the high frequency amplifier 2, the mixing circuits 5 and 6
And the output amplitude of the low-pass filters 7, 8 determined by the characteristics of the low-pass filters 7, 8.

That is, when the frequency spectrum of the signal FSK signal is as shown in FIG. 10, the signal I of FIG. 11 or the signal of FIG. 12 is input to the inputs I and Q of the comparison circuit 13 in accordance with the sign of the frequency displacement δ of the received FSK signal. Appears. In other words, by detecting which of the inputs I and Q is the lead phase,
It is possible to distinguish between + δ and −δ of the frequency shift of the received FSK signal.

The comparison circuit 13 can be easily realized by a D flip-flop or a JK flip-flop, and with the recent technology, the transmitter can easily obtain a stable circuit as an oscillation circuit for the carrier frequency _c and a local oscillation circuit. This device has the advantage that its construction is extremely simple.

[Problems to be solved by the invention]

When this device is used for mobile communication, for example, there is a problem that the envelope of the received wave constantly changes. To solve this problem, an amplitude limiting circuit or an automatic gain control circuit is used. The use of an amplitude limiting circuit is advantageous for constructing a simple receiver. Therefore, conventionally, as described above, the positive / negative of the frequency shift δ is identified by the zero-crossing point of two baseband signals that have passed through the amplitude limiting circuit and are orthogonal to each other.

At this time, the zero-crossing point is π because the signals are orthogonal.
There is a time difference corresponding to a phase difference of / 2. Therefore, the data cannot be determined after the transition of the data until the next transition occurs. In particular, when the transition frequency is small compared to the information transmission rate and one time slot of data is less than the half cycle of frequency deviation, the zero crossing point (rising or rising) of the in-phase signal or quadrature-phase signal is The transition to the next data may occur before the (decrease) occurs. In that case, even if the sign of the received signal changes, the signal cannot be demodulated because it does not pass through the zero crossing point,
It will retain its previous state.

In order to prevent such data loss, the frequency shift δ is considerably larger than the modulation wave frequency _m (corresponding to the frequency at which the frequency shift of the received FSK signal is switched between + δ and −δ, the information transmission rate). It needs to be big. That is, when the modulation frequency _m is increased in order to increase the information transmission rate, the state shown in FIG. 11 transits to the state shown in FIG. 12 or the state shown in FIG. 12 transits to the state shown in FIG. Can't be identified. Practically, it is necessary that δ> 10 _m . Therefore, there is a drawback that the reception speed is limited.

An object of the present invention is to solve the above problems and to provide an FSK signal receiver capable of receiving a high speed signal with a simple circuit configuration.

[Means for solving problems]

The FSK signal receiver of the present invention is characterized by including a second phase shift means for giving a phase difference to two baseband signals which are substantially orthogonal to each other.

It is desirable that the second phase shift means include phase shift circuits having different phase shift amounts inserted in the output circuits of the pair of low pass filters.

There is one local oscillation circuit, and the output of this local oscillation circuit is branched and supplied to the pair of mixing circuits, and the first phase shifting means is one of the branched outputs of this local oscillation circuit. It is desirable to include a π / 2 phase shift circuit inserted in the passage. Further, instead of this configuration, the output of the local oscillation circuit is branched so that the local oscillation signals of the same phase are supplied to the pair of mixing circuits, and the first phase shift means is the FSK of the pair of mixing circuits. It is also possible to adopt a configuration including a π / 2 phase shift circuit inserted in one path of the received signal input.

Each of the output signals of the pair of low-pass filters includes a waveform shaping circuit, the waveform shaping circuit includes an amplifier and an amplitude limiting circuit, and the second phase shifting means includes a front stage or a rear stage of the respective waveform shaping circuits or a waveform shaping circuit. It is desirable to be provided in the circuit.

The second phase shift means includes two phase shift circuits provided in the output signal paths of the pair of low-pass filters and having phase shift amounts of φ ₁ and φ ₂ , respectively, and the phase shift amount is | φ It is desirable that ₁₋ φ ₂ | ≈π / 2.

One of the two phase circuits is a π / 4 phase lead circuit and the other is a π / 4 phase delay circuit, or both of the two phase circuits are phase lead circuits or phase delay circuits. desirable.

The FSK receiver of the present invention further comprises third phase shifting means for branching the two baseband signals to give a phase difference opposite to that of the second phase shifting means, an output of the second phase shifting means and the third phase shifting means. And a comparison means for comparing the output of the phase shift means.

The second phase shifting means and the third phase shifting means respectively include two phase shifting circuits respectively provided in the output signal paths of the pair of low pass filters and having phase shift amounts of φ ₁ and φ ₂ . The phase shift amount is preferably | φ ₁ −φ ₂ | ≈π / 2.

The comparison means includes a first multiplication circuit that multiplies the two output signals of the second phase shift means, a second multiplication circuit that multiplies the two output signals of the third phase shift means, and a second multiplication circuit of the two multiplication circuits. And a subtraction circuit for subtracting the output.

The output signal path of the subtraction circuit preferably includes a waveform shaping circuit, and the waveform shaping circuit preferably includes an amplifier and an amplitude limiting circuit.

[Action]

The FSK signal receiver of the present invention does not identify data at the zero crossings of the output of the amplitude limiting circuit, but rather in the state of two baseband signals. In particular, when the two baseband signals are respectively shifted by the phases φ ₁ and φ _{2 such} that | φ ₁ −φ ₂ | = π / 2, the two baseband signals have the same phase or opposite phases. This allows the data to be determined. Also, changes between "1" and "0" occur simultaneously in the two baseband signals. Therefore, even if one of the baseband signals passes through the zero crossing while one time slot of data continues, the data after identification does not change.

Furthermore, when the third phase shifting means is provided, by comparing the output of the second phase shifting means and the output of the third phase shifting means,
The data can be identified more easily. In particular, when the phase shift difference of π / 2 is given by each of the two phase shift means, the phase shift of each phase shift means becomes the same phase, and the outputs of the two phase shift means become the orthogonal phase shift. Therefore, when the product obtained by multiplying the output of the third phase shifting device is subtracted from the product obtained by multiplying the output of the second phase shifting device, the value is inverted by ± 1 depending on the received data.

〔Example〕

FIG. 1 is a block diagram of the FSK signal receiver according to the first embodiment of the present invention.

This FSK signal receiver includes an antenna 1 for receiving an FSK modulated wave having a frequency _r , a high frequency amplifier 2 for amplifying the received FSK modulated wave to a desired level, and one received FSK signal output by the high frequency amplifier 2. A pair of mixing circuits 5 and 6 provided in a branched manner, a local oscillating circuit 3 which gives the mixing circuits 5 and 6 a local oscillating signal having a frequency substantially equal to the carrier frequency of the FSK signal, and the mixing circuits 5 and 6. A pair of low-pass filters 7 and 8 through which the FSK demodulated signal wave of the output signal passes, respectively, and either the input signals of the mixing circuits 5 and 6 or the local oscillation signal supplied to the pair of mixing circuits 5 and 6 are provided. Is provided with a first phase shifting means for providing a phase difference of approximately .pi. / 2 with a comparison circuit 13 for comparing the output signals of the low-pass filters 7 and 8. In this embodiment, the local oscillator circuit 3
Is one, and the output of the local oscillation circuit 3 is branched and supplied to the pair of mixing circuits 5 and 6. As the first phase shift means, π / 2 that gives a phase difference to the local oscillation signal. The phase shift circuit 4 is used. Further, the receiver of the present embodiment is provided with phase shift circuits 14 and 15 as second phase shift means for giving a phase difference to the output signals of the pair of low pass filters 7 and 8. The phase shift circuits 14 and 15 are inserted in the output circuits of the low-pass filters 7 and 8 and have different phase shift amounts.

Further, the receiver of this embodiment includes waveform shaping circuits in the paths of the output signals of the low-pass filters 7 and 8, respectively, and the waveform shaping circuits include low-frequency amplifiers 9 and 10 and amplitude limiting circuits 11 and 12, respectively. The two phase shift means, that is, the phase shift circuits 14 and 15 are provided at the subsequent stage of each waveform shaping circuit.

The phase shift amounts φ ₁ and φ ₂ by the phase shift circuits 14 and 15 have a relationship of | φ ₁ −φ ₂ | = π / 2 (1).

The outputs of the phase shift circuits 14 and 15 are low frequency amplifiers 9 and 10 in order to eliminate carrier amplitude fluctuations such as fading.
Amplification is performed by and the amplitude is limited by the amplitude limiting circuits 11 and 12. As a result, the outputs of the amplitude limiting circuits 11 and 12 become rectangular waves having a frequency shift period. This digital waveform has the same phase or opposite phase depending on whether the frequency of the received FSK modulated wave is _c ± δ [Hz]. Therefore, the comparison circuit 13
For example, the reception data can be determined by using an exclusive OR circuit.

Here, it is assumed that the local oscillation circuit 3 outputs a local oscillation signal having a frequency _L that is equal to the center frequency _c of the received FSK modulated wave and has the same phase. At this time, the low-pass filter 7,
The I and Q signals output from 8 are It is represented by. Here, the amplitude coefficient is omitted. In response to this signal, the outputs of the phase shift circuits 14 and 15 are Becomes Here, from the formula (1), if φ ₂ = π / 2 + φ ₁ (4), then I _I ′ = cos (2πδt + φ ₁ ) I _Q ′ = ± sin (2πδt + π / 2 + φ ₁ ) = ± cos (2πδt + φ _1). ) …… (5). Further, in the case of φ ₂ = −π / 2 + φ ₁ (4) ′, the sign of the cosine function of the Q signal in the equation (5) is simply inverted. That is, if the expression (1) is satisfied, the two baseband signals have the same phase or opposite phases, and the zero crossing points become the same.

FIG. 2 shows the signal waveform of each part. (a) shows transmission data. (b) and (c) show the output waveforms of the low-pass filters 7 and 8, respectively, (d) and (e) show the output waveforms of the phase shift circuits 14 and 15, and () shows (a). 9 shows an actual output waveform of the phase shift circuit 15 generated by the transmission data shown. Further, (g) and (h) show the output waveforms of the amplitude limiting circuits 11 and 12 for the transmission data of (a), respectively, and (i) shows the output waveform of the comparison circuit 13.

The I signal output from the low-pass filter 7 becomes a sine wave having a frequency deviation as a fluctuating frequency without changing the phase due to the data. Further, the Q signal output from the low-pass filter 8 is phase-inverted depending on the data and becomes either the solid line or the broken line in FIG. 2 (c).

The phase of these signals is φ _{1 in the} phase shift circuits 14 and 15, respectively.
When φ ₂ is changed, the waveforms shown in FIGS. 2 (d) and 2 (e) are obtained. Therefore, when the transmission data has the waveform of FIG. 2 (a), the output of the phase shift circuit 15 has the waveform of FIG. 2 ().

When the outputs of the phase shift circuits 14 and 15 are amplified and the amplitude is limited by the amplitude limiting circuits 11 and 12, digital waveforms I _D and Q _D shown in FIGS. 2 (g) and 2 (h) are obtained. The transmission data can be reproduced by multiplying these waveforms or performing an exclusive OR operation in the comparison circuit 13.

3 and 4 are circuit diagrams showing an example of the phase shift circuits 14 and 15. FIG. 3 shows a phase lead circuit, and FIG. 4 shows a phase delay circuit. These circuits are general circuits using operational amplifiers.

The output waveform of the phase shift circuit ideally changes instantaneously with the transition of data. However, in a realistic circuit, it is necessary to reduce the response time, that is, the transient response, with respect to high-speed signal changes. For that purpose, it is desirable to reduce the time constant of the phase shift circuit. Therefore, it is necessary to make the time constant of the phase shift circuit as small as possible while satisfying the expression (1). Moreover, the time constant of this phase shift circuit is larger than that of other circuits, and the reception speed of this FSK signal receiver is determined by this time constant. Therefore, it is desirable to allocate the phase shift amount of the phase shift circuit as small as possible.

The phase shift circuit shown in FIG. 3 and FIG.
An input signal is supplied to the inverting input of the above through the resistor 32, and the output of the operational amplifier 31 is fed back to the inverting input through the resistor 33. The difference between the phase lead circuit and the phase delay circuit lies in the inverting input circuit of the operational amplifier 31. In the case of a phase lead circuit,
The same input signal supplied to the resistor 32 is connected to the non-inverting input of the operational amplifier 31 via the resistor 34, and this non-inverting input is grounded via the capacitor 35. In the case of a phase delay circuit, the same input signal is connected to the non-inverting input of the operational amplifier 31 via the capacitor 41, and this non-inverting input is grounded via the resistor 42.

Resistors 32 and 33 have the same resistance value, resistors 34 and 42, and capacitor 3
The values of 5 and 41 determine the phase shift amount at a certain frequency. If the respective values are R and C, the phase shift characteristic β (ω) is It is represented by. τ is the time constant of this phase shift circuit.

Here, the phase characteristics at the same frequency, for example, π / 2 and π / 4
Comparing Becomes That is, when it is attempted to obtain twice the amount of phase shift, the time constant, which is a guide for the transient response characteristic, becomes twice or more. Therefore, to receive a faster signal,
It is desirable to allocate a small amount of phase shift to phase shift circuits having opposite polarities. Therefore, as the values of φ ₁ and φ ₂ , φ ₁ = π / 4, φ ₂ = −π / 4 (8) or φ ₁ = −π / 4, φ ₂ = π / 4 ... ( 8) ′ is desirable.

FIG. 5 shows another example of the phase shift circuits 14 and 15.

When the phase characteristics of the phase shift circuits 14 and 15 are constant, the phase shift circuits of FIGS. 3 and 4 can be used. However, generally, the amount of phase shift by the phase shift circuits 14 and 15 changes depending on the frequency. In that case, the phase shift amount φ ₁ , φ
₂ is Equation (1) becomes | Φ ₂ (ω) −Φ ₁ (ω) | = π / 2 (10). Here, Φ ₁ (ω) and Φ ₂ (ω) are functions of frequency.

The problem here is that the spectrum of the transmitted wave becomes wider when the data transmission speed becomes higher. Therefore, in order to receive faster data,
It is necessary to sufficiently pass this spectrum and to shorten the response time for high-speed signal changes. Therefore, the condition of expression (10) needs to have band characteristics. In order to satisfy such a wide band phase characteristic, approximately in a desired band, The condition of must be satisfied.

As the phase shift circuits 14 and 15 satisfying such a condition, it is sufficient that the phase shift amounts Φ ₁ (ω) and Φ ₂ (ω) with respect to frequency are substantially the same and the phase difference is approximately π / 2. For this purpose, both the phase shift circuits 14 and 15 may be phase lead circuits or phase delay circuits.

The phase shift circuit of FIG. 5 shows such an example, and the phase delay circuits shown in FIG. 4 are connected in cascade.

As the phase shift circuits 14 and 15, circuits of the same shape having different time constants are used. Here, when the time constants that determine the phase shift amount φ ₁ of the phase shift circuit 14 are τ ₁ and τ ₂ , and the phase shift amounts φ ₂ of the phase shift circuit 15 are τ ₃ and τ ₄ , respectively, the phase shift amount φ ₁ , φ
₂ is represented by φ ₁ = -2 (tan ω τ ₁ + tan ω τ ₂ ) φ ₂ = -2 (tan ω τ ₃ + tan ω τ ₃ ).

FIG. 6 shows calculated values of the phase shift amounts φ ₁ and φ _{2 with} respect to the frequency and the difference [φ ₁ −φ ₂ ]. The horizontal axis represents frequency, and the vertical axis represents phase shift amount. Here, τ ₁ = 2.2 × 10 ^-5 [seconds] τ ₂ = 4.5 × 10 ^-4 [seconds] τ ₃ = 1.1 × 10 ^-4 [seconds] τ ₄ = 2.3 × 10 ^-4 [seconds].

As shown in FIG. 6, the phase shift amounts φ ₁ and φ ₂ have almost the same slope with respect to the frequency change, and [φ ₁ −φ ₂ ]
Has a phase difference of about 90 ° from about 100Hz to 6KHz. Therefore, in this frequency band, the relative phase difference is almost
It becomes 90 °, and the conditions of formulas (10) and (11) are satisfied.
Therefore, the zero crossing points of the two baseband signals can be set at the same instant in a wide frequency band.

In the above-described embodiments, the phase shift circuits 14 and 15 can be provided after the waveform shaping circuit or in the waveform shaping circuit.

FIG. 7 shows a block diagram of the FSK signal receiver according to the second embodiment of the present invention.

This FSK signal receiver includes an antenna 1 for receiving an FSK modulated wave having a frequency _r , a high frequency amplifier 2 for amplifying the received FSK modulated wave to a desired level, and one received FSK signal output by the high frequency amplifier 2. A pair of mixing circuits 5 and 6 provided in a branched manner, a local oscillating circuit 3 which gives the mixing circuits 5 and 6 a local oscillating signal having a frequency substantially equal to the carrier frequency of the FSK signal, and the mixing circuits 5 and 6. Either the pair of low-pass filters 7 and 8 through which the FSK demodulated signal wave of the output signal passes, and the respective input signals of the mixing circuits 5 and 6 or the local oscillation signal supplied to the pair of mixing circuits 5 and 6 (this In the embodiment, the local oscillation signal) is approximately π / 2.
A first phase shift means for giving a considerable phase difference, and a low pass filter 7,
And a comparison circuit 13 for comparing the output signals of the eight. Also in this embodiment, the number of the local oscillation circuit 3 is one, and the output of the local oscillation circuit 3 is branched and supplied to the pair of mixing circuits 5 and 6, and the local oscillation signal is used as the first phase shifting means. A π / 2 phase shift circuit 4 that gives a phase difference to Further, the receiver of the present embodiment is the second phase shift means for giving a phase difference to the output signals of the pair of low pass filters 7 and 8, that is, a phase shift circuit.
14, 15 and third phase shifting means for branching the output signals of the low-pass filters 7, 8 to give a phase difference opposite to that of the second phase shifting means, that is, phase shifting circuits 14 ', 15', Comparing means for comparing the outputs of the two phase shifting means.

The phase shift amount of the phase shift circuits 14 and 14 ′ is φ ₁ , and the phase shift circuits 15 and 15 ′ are
Is φ ₂ , and there is a relationship of | φ ₁ −φ ₂ | = π / 2.

Further, the comparison means includes a first multiplication circuit 71 that multiplies the two output signals of the phase shift circuits 14 and 15 and a second multiplication circuit 72 that multiplies the two output signals of the phase shift circuits 14 'and 15'. And a subtraction circuit 73 that subtracts the outputs of the two multiplication circuits 71 and 72.

The output signal path of the subtraction circuit 73 includes a waveform shaping circuit,
The waveform shaping circuit is a low frequency amplifier 74 and an amplitude limiting circuit.
Including 75.

In this embodiment, the output signals of the phase circuits 14 and 15 are similar to the equation (5) in the first embodiment, Given in. The phase circuit 14 ', 15' for the output signal _{of, I 14 '= ± sin (} 2πδt + φ 1) I 15' = cos (2πδt + φ 2) = cos (2πδt + φ 1 + π / 2) = -sin (2πδt + φ 2) (13) Here, the expressions (12) and (13) are in the same decoding order.

Of these signals, the outputs of the phase circuits 14 and 15 are multiplied by the multiplication circuit 7
When multiplied by 1, I ₁₄ · I ₁₅ = ± cos ² (2πδt + φ ₁ ) (14) is obtained. Similarly, when the outputs of the phase circuits 14 'and 15' are multiplied by the multiplication circuit 72, Is obtained. In this way, two columns of signals with different polarities are obtained. Next, when the expressions (14) and (15) are subtracted by the subtraction circuit 73, the output S (t) becomes S (t) = ± 1 (16). In this way, the sign of the output of the subtraction circuit 73 is inverted depending on the received data. Data can be demodulated by this code.

By the way, in the configuration in which signals having different polarities are obtained, there is an advantage that the signal-to-noise ratio of the received signal is increased by 3 dB. That is, with respect to the signal S, since the signal whose polarity is inverted is subtracted, the amplitude is doubled. Regarding the noise, since the output signals of the pair of low pass filters are orthogonal to each other, the noise is independent Gaussian noise. This signal is
After that, the phase is shifted to become the same phase, but since it is independent before being shifted, the noise becomes new Gaussian noise. Therefore, the noise power does not change. In the subtraction circuit 73, noise is also orthogonal to each other like the signals shown in the equations (14) and (15), so that it is an independent Gaussian process. Since the subtraction operation is linear combination, it is a Gaussian process again. As a result, the noise power of the obtained signal is unchanged. Therefore, this configuration improves the signal-to-noise ratio by 3 dB.

The output signal of the subtraction circuit 73 is subjected to fading and other amplitude fluctuations by a waveform shaping circuit composed of a low frequency amplifier 74 and an amplitude limiting circuit 75.

FIG. 8 shows a transmission waveform and a reception waveform. (a) shows transmission data, (b) and (c) show outputs of the multiplying circuits 71 and 72, respectively, and (d) shows output of the subtracting circuit 73, respectively. In this way, the original transmission data is demodulated at the output of the subtraction circuit 73.

In the above embodiments, an example in which a phase difference is given to the local oscillation signal as the first phase shifting means has been shown, but a single local oscillation circuit 3 is used, and the output of this local oscillation circuit 3 is branched and paired. It is also possible to use a configuration in which the local oscillation signals of the same phase are supplied to the mixing circuits 5 and 6 of (1) and a π / 2 phase shift circuit inserted in one path of the FSK reception signal input of the mixing circuits 5 and 6 is used.

〔The invention's effect〕

As described above, the FSK signal receiver of the present invention converts a received FSK modulated wave into two baseband signals having the same phase or opposite phases, and outputs data depending on whether they are the same phase or opposite phases. Identify. Since this identification can be easily performed by the logical product circuit or the exclusive OR circuit, the operation of the comparison circuit can be easily speeded up. Furthermore, when two baseband signals are branched into two and the phases are complementarily changed, the received signal can be demodulated simply by multiplying and subtracting signals with different amounts of change, and a simpler circuit The configuration has the effect of demodulating the FSK signal.

The FSK signal receiver of the present invention can receive a high-speed FSK signal, and has an effect that the circuit configuration is simple and the size can be easily reduced.

[Brief description of drawings]

FIG. 1 is a block diagram of the FSK signal receiver according to the first embodiment of the present invention. FIG. 2 is a diagram showing a signal waveform of each part of this receiver. FIG. 3 is a circuit configuration diagram of a phase advance circuit. FIG. 4 is a circuit configuration diagram of the phase delay circuit. FIG. 5 is a circuit configuration diagram showing another example of the phase shift circuit. FIG. 6 is a diagram showing calculated values of the phase shift amounts φ ₁ and φ _{2 with} respect to the frequency and the difference [φ ₁ −φ ₂ ]. FIG. 7 is a block diagram of the FSK signal receiver according to the second embodiment of the present invention. FIG. 8 is a diagram showing a transmission waveform and a reception waveform. 9th is a block diagram of a conventional FSK signal receiver. FIG. 10 is a diagram showing a spectrum of a binary FSK signal. FIG. 11 shows I when the frequency displacement δ of the received FSK signal is positive.
The figure which shows the phase relationship of a signal and a Q signal. FIG. 12 shows I when the frequency displacement δ of the received FSK signal is negative.
The figure which shows the phase relationship of a signal and a Q signal. 1 ... Antenna, 2 ... High frequency amplifier, 3 ... Local oscillation circuit, 4 ... π / 2 phase shift circuit, 5, 6 ... Mixing circuit,
7,8,74 ... Low-pass filter, 9,10 ... Low-frequency amplifier,
11, 12, 75 …… Amplitude limiting circuit, 13 …… Comparison circuit, 14, 1
4 ', 15, 15' ... phase shift circuit, 71, 72 ... multiplication circuit, 73 ...
… Subtraction circuit.

Claims (13)

[Claims] 1. A pair of mixing circuits to which one received FSK signal is branched and applied, a local oscillating circuit for giving a local oscillating signal having a frequency substantially equal to the carrier frequency of the FSK signal to the mixing circuit, and the pair of mixing circuits. A pair of low-pass filters through which the FSK demodulated signal waves of the output signals of the mixing circuit pass, respectively, and each of the input signals of the pair of mixing circuits or the local oscillation signal supplied to the pair of mixing circuits is substantially In an FSK signal receiver including a first phase shifting means for providing a phase difference equivalent to π / 2, and a comparison circuit for comparing output signals of the pair of low-pass filters, each of the pair of low-pass filters An FSK signal receiver comprising a second phase shift means for applying a phase difference to output signals. 2. The FSK signal receiver according to claim 1, wherein the second phase shift means includes phase shift circuits having different phase shift amounts inserted in respective output circuits of the pair of low pass filters. 3. A local oscillation circuit is one, and the output of this local oscillation circuit is branched and supplied to a pair of mixing circuits, and the first phase shifting means is branched to this local oscillation circuit. The FSK signal receiver according to claim 1, further comprising a π / 2 phase shift circuit inserted in one path of the output. 4. A local oscillating circuit is provided, and an output of this local oscillating circuit is branched so that a local oscillating signal of the same phase is supplied to a pair of mixing circuits. The FSK signal receiver according to claim 1, further comprising a π / 2 phase shift circuit inserted in one path of the FSK reception signal input of the pair of mixing circuits. 5. A waveform shaping circuit is included in each of the paths of the output signals of the pair of low pass filters, the waveform shaping circuit includes an amplifier and an amplitude limiting circuit, and the second phase shifting means is provided in front of each of the waveform shaping circuits. The FSK signal receiver according to claim 1, which is provided in a subsequent stage or in the waveform shaping circuit. 6. The second phase shift means includes two phase shift circuits provided in the output signal paths of the pair of low-pass filters and having phase shift amounts of φ ₁ and φ ₂ , respectively, The FSK signal receiver according to claim ₁ , wherein the transition amount is | φ ₁ −φ ₂ | ≈π / 2. 7. The FSK signal receiver according to claim 6, wherein one of the two phase shift circuits is a π / 4 phase advance circuit and the other is a π / 4 phase delay circuit. 8. The FSK signal receiver according to claim 6, wherein both of the two phase circuits are phase lead circuits. 9. The FSK signal receiver according to claim 6, wherein both of the two phase circuits are phase delay circuits. 10. A pair of mixing circuits to which one received FSK signal is branched and applied, a local oscillating circuit for giving a local oscillating signal of a frequency substantially equal to the carrier frequency of the FSK signal to the mixing circuit, and the pair of mixing circuits. A pair of low-pass filters through which the FSK demodulated signal waves of the respective output signals of the mixing circuit pass, and either of the input signals of the pair of mixing circuits or the local oscillation signal supplied to the pair of mixing circuits are approximately π /
FSK provided with a first phase shift means for providing a phase difference of 2
In the signal receiver, second phase shift means (14, 15) for giving a phase difference to each output signal of the pair of low-pass filters, and branching each output signal of the pair of low-pass filters, Third phase shifting means (14 ', 1 which gives a phase difference opposite to the second phase shifting means)
5 ') and a comparing means for comparing the output of the second phase shifting means with the output of the third phase shifting means. 11. A second phase shift means and a third phase shift means are provided in respective output signal paths of a pair of low pass filters,
11. The FSK signal receiver according to claim 10, which includes two phase shift circuits each having a phase shift amount of φ ₁ and φ ₂ , and the phase shift amount is | φ ₁ −φ ₂ | ≈π / 2. 12. Comparing means includes a first multiplication circuit (71) for multiplying two output signals of the second phase shift means, and a second multiplication circuit for multiplying two output signals of the third phase shift means. The FSK signal receiver according to claim 11, comprising: (72); and a subtraction circuit (73) for subtracting the outputs of the two multiplication circuits. 13. The FSK signal receiver according to claim 12, wherein a waveform shaping circuit is included in the path of the output signal of the subtraction circuit, and the waveform shaping circuit includes an amplifier and an amplitude limiting circuit.