JP3422484B2 - Demodulation circuit and receiving device having the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to angle modulation and ASK (Amplitude Shift Keyin) of one carrier with two kinds of information signals.
g) The present invention relates to a demodulation circuit that obtains the above-mentioned two types of information signals by respectively demodulating the signals obtained by the modulation, and a receiving device having the demodulation circuit.

For example, in a road-to-vehicle information system,
FSK (Frequency Sh
GMSK (Gaussian Min), which is a type of ift keying) modulation
imumShift Keying) Modulation is applied. The obtained GMSK modulated signal of constant amplitude is further processed by an information signal of information for detecting the position and direction, and further with a modulation factor of 1 kHz.
It is ASK-modulated at 0% and wirelessly transmitted as a 2.5 GHz band signal. When receiving the GMSK / ASK modulated signal, it is necessary to demodulate each of the GMSK modulated signal and the ASK modulated signal by the in-vehicle receiver to obtain each information signal.

[0003]

2. Description of the Related Art Generally, an FM detection device can be considered as an angle modulation signal detection device, and an AM detection device can be considered as an ASK detection device. An FM detector and an AM detector, both of which are configured by one circuit, are disclosed in, for example, Japanese Patent Laid-Open No. 1-261.
As shown in Japanese Patent Laid-Open No. 008, a configuration is conceivable in which an AM detection method of logarithmically converting an amplitude detection signal, direct current cutoff, and antilogarithmic conversion, and an FM detection method using a limiter amplifier and an FM detector are combined. .

[0004]

In mobile radio communication, deterioration of a transmission signal called fading is known due to multiple wave interference due to reflection and the like. For example, in a road-to-vehicle information system, a modulated signal is transmitted at a radio frequency of 2.5 GHz band, so that the speed is 100 k / h.
When received by a car running at m, it is affected by fading with a fading pitch of 1/230 seconds.
Therefore, the input level of the received signal is the highest frequency 230H.
There is a large fluctuation in z (20 dB to 30 dB fluctuation). The receiving device is required to demodulate a 1 kHz ASK modulated signal having a modulation factor of 10% from this received signal.

When the modulated signal affected by fading is subjected to AM detection, a signal in which an ASK modulated signal component and an amplitude fluctuation component due to fading are superimposed is output. At this time, the amplitude of the ASK modulation signal component included in the output signal of the AM detector largely changes according to the fluctuation of the input level due to fading. For example, when the input level fluctuates by 30 dB, the ASK modulation signal component Amplitude is also 30 dB
fluctuate. Therefore, when converting into digital data with a comparator or the like, a highly accurate comparator or amplifier is required, which is not practical.

An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a demodulation circuit capable of reducing fluctuations of a demodulation signal due to fading and the like as much as possible, and a receiver using the demodulation circuit. is there.

[0007]

In order to achieve the above-mentioned object, according to the present invention, there is provided a detection circuit section for amplitude-detecting an angle / ASK modulated signal, logarithmically converting the obtained amplitude-detected signal, and outputting the result. , Of the signals included in the logarithmically converted amplitude detection signal, unnecessary signals such as amplitude fluctuations due to fading or the like are removed, and the ASK detection signal is passed through to output a filter and an output signal of the filter. A mobile unit that receives the input signal, converts the output signal into digital data, and outputs the digital data.
Good for communication using ASK modulated wave in communication.
A suitable demodulation circuit was constructed.

[0008]

The logarithmically converted amplitude detection signal always contains an ASK modulation signal component having a constant amplitude even if the input level fluctuates greatly due to fading or the like. Therefore, A
The logarithmically converted amplitude detection signal is filtered by a filter that allows the SK modulated signal to pass but eliminates amplitude fluctuations due to fading, etc.
The SK detection signal can be obtained. Therefore, when the range in which the amplitude detection is performed and the logarithmic conversion is performed and output is wide, in other words, when the dynamic range of the input level of the demodulation circuit is wide, a complicated AGC circuit is not required.
Therefore, the circuit scale can be reduced. In addition, by converting the output signal to digital information by the conversion means and outputting the digital information, the processing device for processing the output signal (digital data) is simpler than any other case as compared with the case of outputting the analog signal as it is without any special consideration. Can be configured to.

[0009]

Embodiments of the present invention will be described in detail below with reference to the drawings. As the angle modulation signal, FM signal, PS
K signal, FSK signal, MSK signal, GMSK signal, QA
Although the M signal and the like are known, the GMSK signal will be representatively described here.

FIG. 1 is a block diagram showing the concept of a demodulation circuit according to the present invention. GMSK supplied to input terminal 1
The amplitude of the ASK modulated signal is limited by the limiter amplifier 11 in the detection circuit unit 10, and the FM detector 12
Frequency detection is performed by the GMSK detection signal output terminal 2 as a result.
Is output to.

Further, GMSK supplied to the input terminal 1
The ASK modulated signal is subjected to envelope detection by the AM detector 13 and logarithmically converted by the logarithmic converter 14 in the detection circuit unit 10.

Here, the logarithmic conversion operation in the logarithmic converter 14 will be described with reference to FIG. FIG. 2 is an explanatory diagram showing the characteristics of the logarithmic converter 14 in FIG. The characteristic of the logarithmic converter 14 is a straight line as shown in FIG. 2, where the horizontal axis is the log scale and the vertical axis is the linear scale.

Now, due to fading, etc., GMSK
When the amplitude of the ASK modulated signal fluctuates in a fast cycle, the amplitude of the modulated signal input to the detection circuit unit 10 largely fluctuates. Therefore, the amplitude detection signal obtained by detecting this modulated signal by the AM detector 13 is also as shown in A of FIG. 2 (A is drawn on a log scale).
The amplitude greatly changes, and the amplitude of the ASK modulation signal component included in the amplitude detection signal also largely changes as indicated by a ₁ and a ₂ .

However, due to fading, etc., GMS
Even if the amplitude of the K · ASK modulated signal varies greatly, the ASK modulated signal is always included in the modulated signal at a constant rate according to the modulation degree. Therefore, the amplitude detection signal obtained by detecting the modulated signal by the AM detector 13 is logarithmically converted by the logarithmic converter 14, so that the amplitude detection signal becomes as shown in B of FIG. Is drawn on a linear scale), and the amplitude of the ASK modulation signal component contained in this amplitude detection signal is always a constant amplitude as shown by b ₁ and b ₂ . That is, the output of the logarithmic converter 14 is an amplitude detection signal in which an ASK modulation signal component having a constant amplitude and an unnecessary amplitude fluctuation component due to fading are superimposed.

Thereafter, the logarithmically converted amplitude detection signal is filtered by a band-pass filter (BPF) 20 which passes an ASK modulation signal component but removes an unnecessary amplitude fluctuation component due to fading or the like, and as a result. , The ASK detection signal which is a good ASK modulation signal with a constant amplitude is ASK
It is output from the detection signal output terminal 3.

Here, the BPF is used as means for removing an unnecessary amplitude fluctuation component due to fading or the like from the logarithmically converted amplitude detection signal. However, when the frequency band of the unnecessary amplitude fluctuation component due to fading is lower than the frequency band of the ASK modulated signal,
Instead of the BPF 20, a high-pass filter (HP) having a cutoff frequency that is lower than the frequency band of the ASK modulation signal and higher than the frequency band of an unnecessary amplitude fluctuation component due to fading or the like.
F) may be used.

The performance required for these filters will be described below by taking the road-vehicle information system as an example. FIG. 3 is an explanatory diagram showing the relationship between the attenuation characteristic of the filter and the ASK modulation signal component and unnecessary amplitude fluctuation component when the HPF is used as the filter.

As described above, when a 2.5 GHz radio signal is received by an automobile running at a speed of 100 km / hour, it is affected by fading at a maximum frequency of 230 Hz. The frequency components of unnecessary amplitude fluctuations due to fading are distributed as shown in FIG. On the other hand, when the signal transmitted by ASK modulation is a square wave of 1 kHz, this square wave is 1 kHz, 3 kHz, 5 kHz by Fourier transform.
It can be seen that it is composed of frequency components of Hz, .... Therefore, the HPF is required to have a performance of attenuating 230 Hz and passing 1 kHz or more as shown in FIG.

FIG. 4 is an explanatory diagram showing the relationship between the attenuation characteristic of the filter and the ASK modulation signal component and unnecessary amplitude fluctuation component when the BPF is used as the filter. HPF
The difference from the above case is that a filter which passes at least the fundamental wave of the ASK modulated signal and attenuates 230 Hz is used. In the road-to-vehicle information system, the transmission rate is 6
Since GMSK modulation of 4 kbps is performed at the same time, FM-AM conversion may occur due to the slope of the frequency characteristic of the transmission line, and the amplitude of the modulated signal may fluctuate depending on the GMSK signal. Therefore, as in this example, B
By using the PF, interference due to FM-AM conversion and high frequency noise can be reduced.

FIG. 5 is a block diagram showing an expanded concept of the demodulation circuit according to the present invention. 5, the same reference numerals as those in FIG. 1 have the same functions. The points different from those shown in FIG. 1 will be described below.

The logarithmically converted amplitude detection signal input to the automatic gain control (AGC) signal generator 40 is passed by a low pass filter (LPF) 42 having a cutoff frequency lower than the frequency band of the ASK modulation signal. The gain control amplifier 30 is filtered and compared with a reference value arbitrarily set by the comparison circuit 41. Based on the comparison result, the gain control of the gain control amplifier 30 is performed so that the output of the LPF 42 becomes the set value.

Therefore, for example, a relatively slow modulated signal such as a change in the distance from the transmitting antenna, a gain deviation of an amplifier in manufacturing the receiver, and a low frequency fluctuation component among unnecessary amplitude fluctuations due to fading or the like. Fluctuation of
This gain control amplifier 30 can be relaxed, and has an effect of expanding the range of reception levels that can be demodulated.

Based on the above, FIG. 6 is a block diagram showing a demodulation circuit as an embodiment of the present invention. 6, the same reference numerals as those in FIG. 1 have the same functions. In this embodiment, the GMSK / ASK modulated signal is input terminal 1
Further, the demodulated data is input from the GMSK demodulated data output terminal 4 and the ASK demodulated data output terminal 5 is output.

By connecting the output of the FM detector 12 to the BPF 50 having the pass band in the frequency band of the GMSK modulation signal, noise in the GMSK detection signal can be reduced and a better detection signal can be obtained. You can

Since GMSK modulation is a kind of FM modulation, it can be detected by the same method as FM detection. However, unlike FM modulation, which requires analog information,
The information necessary for demodulating the GMSK modulated signal is "1" or "0" digital information. Further, the demodulation of the ASK modulated signal is similar to the GMSK modulation.

Therefore, by connecting the comparators 60 and 70 for converting the detection output into digital information and outputting the digital information, a demodulation circuit which can be easily connected to an external digital circuit through the demodulation data output terminals 4 and 5 is provided. Can be provided. For example, the outputs of the comparators 60 and 70 are T
If the TL input signal is adapted, the output signal of the demodulation circuit can be directly input to the digital TTL circuit.

Therefore, when outputting an analog signal,
Although it is necessary to sufficiently consider the impedance and the level of the output side and the input side, the obtained data is processed by being converted into digital information and output by the comparators 60 and 70 as in the present embodiment. It is possible to obtain the effect that the processing apparatus for performing the processing can be easily configured.

Although only the case of outputting binary data has been described here, the comparators 60 and 70 may be replaced with A / D converters, or a multivalued data determination may be performed by a comparator having a plurality of reference values. It is clear that the present invention is also effective when performing and outputting.

FIG. 7 is a block diagram showing a receiving apparatus as an embodiment of the present invention. 7, the same reference numerals as those in FIG. 1 have the same functions. High carrier frequency G
The MSK / ASK modulated signal is input to the input terminal 6.
In the tuner section 80, this modulated signal is filtered by a BPF 81 that allows the input modulated signal to pass but removes other unnecessary signals, is amplified by a high frequency amplifier 82, and is oscillated by an oscillator frequency control circuit 83. The frequency conversion circuit 85 performs frequency conversion using the output of the controlled frequency variable oscillation circuit 84.

The modulated signal frequency-converted by the frequency conversion circuit 85 is amplified by an intermediate frequency (IF) amplifier 90, and is filtered by a BPF 100 that allows the modulated signal to pass but removes unnecessary signals such as other noises. It The output of the BPF 100 is demodulated by the demodulation circuit described above with reference to FIG. 1 and a detection signal is output.

If the dynamic range of the input level of the demodulation circuit is sufficient in the application system, the complicated AGC circuit generally used for demodulating the ASK modulated signal is not required. Therefore, the size of the receiving device can be reduced.

FIG. 8 is a block diagram showing a receiving apparatus as another embodiment of the present invention. In FIG. 8, the same reference numerals as those in FIGS. 5 and 7 have the same functions. In the present embodiment, the high frequency amplifier 82 in the embodiment of FIG. 7 described above is replaced with a gain control high frequency amplifier 86, and the IF amplifier 90 is replaced with a gain control amplifier 30, respectively, and the AGC signal generator 40 described in FIG. Output by amplifier 8
6 and the gain of the amplifier 30 are controlled. At this time, the AGC signals of the amplifier 86 and the amplifier 30 do not have to be the same. As shown in FIG. 8, the time constant of the AGC signal can be changed by passing through the LPF 43 and can be selected depending on the applied system.

By providing the gain control means, for example, a change in the distance from the transmitting antenna, a gain deviation of the amplifier in the manufacture of the receiver, and a fluctuation component of a low frequency among unnecessary amplitude fluctuations due to fading, etc. The slow fluctuation of the modulated signal can be alleviated by the amplifier 86 and the amplifier 30, which has the effect of expanding the demodulating reception level range.

FIG. 9 is a block diagram showing a receiving apparatus as another embodiment of the present invention. In FIG. 9, the same symbols as those in FIG. 7 have the same functions. In this embodiment, an amplitude detection signal output terminal 7 for outputting a logarithmically converted amplitude detection signal is further provided in the configuration of FIG. By providing this amplitude detection signal output terminal 7, it is possible to easily detect the reception level outside the receiving device and to perform control using the amplitude detection signal.

Therefore, when processing each demodulated detection signal, it is possible to process reception level information and the like at the same time. For example, when the reception level becomes lower than the set value, the GMSK detection signal from the GMSK detection signal output terminal 2 is not used, or if the received information is the same information that is repeatedly transmitted, demodulation is performed. It is possible to perform processing such as lowering the priority of the information of the detected signal. As a result, it is possible to obtain the effect of providing more accurate information to the user.

FIG. 10 is a block diagram showing a receiving apparatus as still another embodiment of the present invention. 10, the same reference numerals as those in FIG. 8 have the same functions. In the present embodiment, an AGC signal output terminal 8 for outputting all or part of the AGC signal is further provided in the configuration of FIG. 8 described above. By providing this AGC signal output terminal 8, it is possible to facilitate the detection of the reception level outside the receiving device and the control using the AGC signal signal, as in the embodiment of FIG. 9 described above. The same effect as that of the embodiment of FIG. 9 can be obtained.

The embodiments of the present invention have been described above. In the demodulation circuit and the receiving device described above,
If the detection circuit unit 10 is configured by an integrated circuit (IC), it is easy to increase the accuracy of the circuit element and stable demodulation performance of the receiving device can be obtained. Further, there is an effect that high-density mounting can be achieved and the demodulation circuit or the receiving device can be downsized.

In the receiving device, the arrangement of circuits such as a high frequency circuit on the substrate is also an important factor for improving the performance of the receiving device. FIG. 11 shows FIG.
FIG. 3 is a layout diagram showing an example of a circuit layout of the receiving apparatus of FIG.

GMSK · A supplied to the input terminal 201
The SK modulated signal is processed by the radio frequency (RF) processing block 3
In 03, as already explained, filtered and amplified,
The frequency is converted by the frequency conversion circuit using the local oscillation signal from the local oscillator block 304 controlled by the local oscillator frequency control block 302. The frequency-converted GMSK / ASK modulated signal is demodulated in the IF processing / demodulation block 301, and the GMSK detection signal is logarithmically converted from the GMSK detection signal output terminal 202 and the ASK detection signal from the ASK detection signal output terminal 203. The amplitude detection signal is output from the amplitude detection signal output terminal 204.

Here, as shown in FIG. 11, the input terminal 2
The local oscillator block 304 and the local oscillator frequency control block 302 are arranged close to one side farthest from the one side closest to 01. With this arrangement, it is possible to reduce the leakage of the local oscillation output signal from the input terminal 201, and it is possible to obtain the effect of reducing the influence on other radio systems that use frequencies near the fundamental and harmonic frequencies of the local oscillation signal. You can

The output terminals 202, 203 shown in FIG.
The placement order of 204 should be adapted to the device used and is not limited by FIG. Also, G
GMSK demodulation data instead of the MSK detection output signal,
Even if the ASK demodulation data is output instead of the ASK detection signal and the AGC signal is output instead of the logarithmically converted amplitude detection output signal, it is apparent that the effectiveness of the present invention does not change at all.

In the above description, GMSK / ASK modulation is taken as an example of the angle / ASK modulation, and the case of demodulating the modulated signal is described, but the invention is not limited to demodulation of the GMSK / ASK modulated signal. Further, as the wave detector, other angle modulation wave detecting means may be used instead of the FM wave detector, and other amplitude detecting means may be used instead of the AM wave detector. It is obvious that

In the FM receiver and the FSK receiver, the amplitude detection signal of the input signal is logarithmically converted and RSSI (Recieved).
Signal Strength Indicator) Some are output as signals. The present invention can be easily realized by using such a receiving device. Also, this RSSI
The FM detection circuit having the output function is integrated,
By using this integrated circuit, the present invention can be easily realized in a small size and easily.

[0044]

As described in detail above, according to the present invention, in the case of simultaneously demodulating signals which are angle / ASK modulated, a detection circuit unit for outputting an amplitude detection signal logarithmically converted to ASK demodulation is required. ASK detection output signal having a constant amplitude can be obtained by demodulating in combination with a filter that filters all or part of the ASK modulated signal.
Good ASK demodulation can be performed even under the influence of fading, which is a problem in mobile radio communication.

Further, by arranging the local oscillator and the local oscillator frequency control circuit close to one side farthest from the one side closest to the input terminal, it is possible to prevent the local oscillator output signal from leaking from the input terminal. Therefore, it is possible to obtain the effect of reducing the influence on other wireless systems.

[Brief description of drawings]

FIG. 1 is a block diagram showing a concept of a demodulation circuit according to the present invention.

FIG. 2 is an explanatory diagram showing characteristics of a logarithmic converter 14 in FIG.

FIG. 3 is an explanatory diagram showing a relationship between an attenuation characteristic of a filter and an ASK modulation signal component and an unnecessary amplitude fluctuation component when an HPF is used as the filter.

FIG. 4 is an explanatory diagram showing the relationship between the attenuation characteristic of the filter, the ASK modulation signal component, and the unnecessary amplitude fluctuation component when the BPF is used as the filter.

FIG. 5 is a block diagram showing an expanded concept of the demodulation circuit according to the present invention.

FIG. 6 is a block diagram showing a demodulation circuit as one embodiment of the present invention.

FIG. 7 is a block diagram showing a receiving device as an embodiment of the present invention.

FIG. 8 is a block diagram showing a receiving device as another embodiment of the present invention.

FIG. 9 is a block diagram showing a receiving device as another embodiment of the present invention.

FIG. 10 is a block diagram showing a receiving device as still another embodiment of the present invention.

11 is a layout diagram showing an example of a circuit layout of the receiving apparatus of FIG. 9. FIG.

[Explanation of symbols]

1 ... GMSK / ASK modulated signal input terminal 2 ... GMSK detection signal output terminal 3 ... ASK detection signal output terminal 4 ... GMSK demodulation data output terminal 5 ... ASK demodulation data output terminal 6 High frequency GMSK / ASK modulated signal input terminal 7 ... Amplitude detection signal power terminal 8 ... AGC signal output terminal 10 ... Detection circuit section 11 ... Limiter amplifier 12 ... FM detector 13 ... AM detector 14 ... Logarithmic converter 20 ... BPF 60, 70 ... Comparator 201 ... High frequency GMSK / ASK modulated signal input terminal 301 ... IF processing, demodulation block 302 ... Local oscillator frequency control block 303 ... RF processing block 304 ... Local oscillator block

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshio Nagashima, 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa, Hitachi, Ltd., Visual Media Research Laboratories (56) References JP-A-2-222233 (JP, A) Kaihei 2-288513 (JP, A) JP 52-42011 (JP, A) JP 62-188404 (JP, A) JP 64-47134 (JP, A) JP 63-292805 ( (58) Fields investigated (Int.Cl. ⁷ , DB name) H04L 27/06 H04B 1/10 H04L 27/14

Claims (9)

(57) [Claims] 1. A demodulation circuit for demodulating a modulated signal obtained by ASK-modulating a carrier wave with an information signal and outputting the information signal, wherein an ASK modulation wave is used in mobile communication.
In a demodulation circuit suitable for use in communication, a detection circuit unit for inputting the modulated signal, amplitude-detecting the modulated signal to obtain an amplitude detection signal, and logarithmically converting the amplitude detection signal for output. A filter and an output signal of the filter that remove unnecessary signal components from the signal components included in the detection output output from the detection circuit unit and allow the information signal component to pass therethrough and output. And a conversion means for converting the output signal into digital data and outputting the digital data. 2. The demodulation circuit according to claim 1, wherein the filter is a bandpass filter. 3. The demodulation circuit according to claim 1, wherein the detection circuit unit is an integrated circuit. 4. The demodulation circuit according to claim 1, 2, or 3, wherein the amplitude detection signal output from the detection circuit unit is input, and an automatic gain control signal is generated based on the amplitude detection signal. An automatic gain control signal generation unit for outputting, the modulated signal is input, the modulated signal is amplified and output, and the gain is determined by the automatic gain control signal output from the automatic gain control signal generation unit. And a variable gain control amplifier to be controlled, wherein the detection circuit section receives the modulated signal output from the variable gain control amplifier. 5. A receiving device for receiving a modulated signal obtained by angle-modulating one carrier wave with a first information signal and ASK-modulating with a second information signal, which is A in mobile communication.
A demodulation circuit suitable for communication using SK modulated waves
In a receiving device having, a tuner unit for inputting the modulated signal, frequency-converting and outputting the modulated signal at least once, and inputting the modulated signal output from the tuner unit,
The demodulation circuit according to claim 1, 2, 3, or 4, which demodulates the modulated signal and outputs the first and second information signals, respectively. 6. A receiver for receiving a modulated signal obtained by angle-modulating one carrier wave with a first information signal and ASK-modulating with a second information signal, which is A in mobile communication.
A demodulation circuit suitable for communication using SK modulated waves
In a receiving device having, a tuner unit for inputting the modulated signal, frequency-converting and outputting the modulated signal at least once, and inputting the modulated signal output from the tuner unit,
The demodulation circuit according to claim 4, which demodulates the modulated signal and outputs the information signal, wherein the tuner unit inputs the modulated signal into a signal path of the modulated signal. And a variable gain control amplifier which amplifies and outputs the modulated signal, and whose gain is controlled by the automatic gain control signal output from the automatic gain control signal generating section. . 7. The receiving device according to claim 5, wherein the receiving device has a function of outputting all or part of the amplitude detection signal output from the detection circuit unit to the outside of the device. apparatus. 8. The receiving device according to claim 6, wherein the receiving device has a function of outputting all or a part of the automatic gain control signal output from the automatic gain control signal generation unit to the outside of the device. Receiving device. 9. The receiving device according to claim 5, 6, 7 or 8, wherein the tuner section amplifies or filters the input terminal for inputting the modulated signal and the input modulated signal. A high-frequency processing unit that outputs a local oscillation signal, a local oscillation unit that generates a local oscillation signal, a local oscillation frequency control unit that controls the oscillation frequency of the generated local oscillation signal, and the modulated signal output from the high-frequency processing unit. A frequency conversion unit that converts the frequency of the signal based on the generated local oscillation signal and outputs the frequency-converted signal, and when arranging each component of the tuner unit on the substrate, the arrangement of the input terminal The local oscillation section and the local oscillation frequency control section are arranged near one side of the substrate closest to a position farthest from the one side.