JPS6312426B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a receiver that receives a signal that is angle-modulated by a digital signal.

Conventionally known disk detection digital signal receivers take time to compensate for variations in carrier frequency or changes in disk center frequency, and especially when communicating alternately, it takes time to compensate for changes in the carrier frequency or center frequency of the disk. The drawback was that it started up slowly.

An object of the present invention is to provide a digital radio receiver in which the start-up of each communication, except for the first communication, is quick even when the carrier frequency or the center frequency of the disk varies, even when the communication is performed alternately. There is a particular thing.

According to the present invention, a circuit is provided that detects a direct current imbalance in the output of the demodulator as an error, and the potential difference between the demodulator output and the reference potential of the determination circuit is controlled by this error signal, or By controlling the local oscillation frequency of the frequency converter provided before the demodulator and switching the time constants of these control operations by the output of the input signal detector,
The above objective can be achieved.

This will be explained in detail below using the drawings. Figure 1 shows
1 is a diagram showing an example of the configuration of a conventional digital FM radio receiver.

The signal input from the terminal 1 is applied to the frequency converter 3 together with the output of the local oscillator 4 to become an intermediate frequency band signal, which is passed through the bandpass filter 5 and then demodulated by the frequency discriminator 6. . After noise is removed from the demodulated signal by a low-pass filter 7, it is judged by a decision circuit 8 in synchronization with a clock signal obtained by a clock regeneration circuit 10, and a transmission digital signal is obtained. Low pass filter 9 is carrier frequency or frequency discriminator 6
The average value is calculated to detect fluctuations in the center frequency.

FIG. 2 schematically shows the output of the frequency discriminator for two different input carrier frequencies. In the figure, the time interval T is a clock cycle, and the signal is determined at the time indicated by the arrow in the figure. At this time, the reference voltage for determination is selected as shown by the constant chain line. Figure a is an ideal case.
When the carrier frequency or the center frequency of the frequency discriminator changes, the output of the frequency discriminator changes overall by △V, as shown in Figure b.
For optimal reception, the reference voltage must be varied as the carrier frequency and the center frequency of the frequency discriminator change.

Low-pass filter (hereinafter referred to as LPF) in Figure 1
9 calculates the average value or error from the demodulated output,
The reference voltage for determination is changed by this error output. At this time, if the cutoff frequency of LPF9 is increased, the reference voltage changes depending on the distribution of the received signal, making the operation unstable. On the other hand, if the cutoff frequency is lowered, this problem will disappear, but the reception A contradiction arises in that the rise time becomes longer. This is not a big problem in high-capacity digital wireless systems where communication is performed continuously. However, in a mobile communication system in which communication is performed alternately, a long start-up time is required for each call, which poses a major problem.

FIG. 3 is a block diagram showing a first embodiment of the present invention. The difference from the conventional embodiment shown in FIG. 1 is that a circuit 11 for detecting signal strength is provided, and the cutoff frequency of the LPF 9' is switched by the output of this circuit. When the received signal is interrupted, the signal detection circuit 11 detects this,
The cutoff frequency of the LPF 9' is switched to a low value, and the reference voltage of the determiner 8 is maintained. said LPF for at least the length of time that a speaker with this receiver continues to speak.
If the time constant determined by the cut-off frequency is increased, the reference voltage of the determiner 8 will hold the previous value until the other party transmits and the next party receives. Carrier wave frequency fluctuations and frequency discriminator center frequency fluctuations are mainly due to ambient temperature changes, so changes during a call can be ignored, so the held reference voltage will remain at the correct value even in the next reception state. It's getting old. As can be seen from the above description, the receiver according to the present invention only requires a slightly longer startup time when starting a call for the first time, but this startup time will not be a problem when communicating alternately thereafter. .

FIG. 4 shows an embodiment in which the present invention is applied to another conventional circuit, in which fluctuations in carrier frequency are changed by changing the oscillation frequency of the local oscillator 3 applied to the frequency converter 3 by the same amount. Until now, it has been known that it is possible to compensate for However, in the conventional method, there is a contradiction between the rise time during reception and the stable operation of the determiner 8, as described above. In this embodiment as well, if the output of the LPF 9' is held by the signal strength detector 11, the local oscillation frequency once correctly matched in the first communication will not change during alternate communications, and the rise time This solves the problem of long times.

FIG. 5 is a block diagram showing a third embodiment of the invention. In this embodiment, a delay detector 6' shown surrounded by a broken line in the figure is used as a demodulator instead of a frequency discriminator. The delay detector delays one of the signals by an appropriate time τ using a delay circuit 12, and uses a phase comparator 17 to determine the phase difference between the signal and the original signal. If the delay time τ is made infinitely small, the operation becomes the same as that of a frequency discriminator. Since the operation of such a detection method is well known, a detailed explanation will be omitted here, but it is the same that the average value of the demodulated output changes when the carrier frequency changes. The operation of this embodiment is the same as that shown in FIG. 4, except for the detection method.

As shown in the above embodiments, the reception detector 11
The time constant of must be smaller than that of LPF9'. The operation of the signal detector 11 is well known and has not been explained in detail, but for example, it can be thought of in the same way as the squelch detection circuit of an FM radio. Possible methods include methods for detecting Also, the means to obtain the error signal is the LPF shown here.
This method is not limited to the above method, but a method using the results determined once is equally effective.

Furthermore, if the LPF is configured as a digital circuit with memory, the signal holding time can be made infinite.

As described above, the present invention has the effect that when communication is performed alternately, the start-up of communication is faster each time even if the carrier wave frequency fluctuates.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a conventional digital FM receiver, Fig. 2 is a schematic diagram of the demodulation circuit output waveform to explain the operation of the receiver shown in Fig. 1, and Fig.
The figure is a block diagram showing a first embodiment of the present invention, FIG. 4 is a block diagram showing a second embodiment, and FIG. 5 is a block diagram showing a third embodiment. In the figure, 1... input terminal, 2... output terminal, 3... frequency converter, 4... local oscillator,
4'... Voltage controlled local oscillator, 5... Band pass filter, 6... Frequency discriminator, 6'... Delay detector, 7... Low pass filter, 8... Determiner, 9
...Low pass filter, 9'...Low pass filter with variable cutoff frequency, 10...Clock extractor, 11...Signal detector, 12...Delay circuit, 13...Phase comparison.

Claims (1)

[Claims] 1. In a receiver having a demodulator that demodulates a signal angle-modulated by a digital signal and a determination circuit that determines the demodulation result, the DC imbalance of the output of the demodulator is A circuit for detecting an error, a circuit for controlling the potential difference between the output of the demodulator and a reference potential of the determination circuit using the error signal, and means for detecting the strength of the input signal, A digital radio receiver characterized in that a constant is switched by the output of the means for detecting the intensity of the input signal. 2. In a receiver having a demodulator that demodulates a signal angle-modulated by a digital signal, a circuit that detects DC imbalance of the output of the demodulator as an error, and a circuit that detects the DC imbalance of the output of the demodulator as an error, and A circuit for controlling the local oscillation frequency of a frequency converter provided before the input of the device and means for detecting the intensity of the input signal are provided, and the time constant of the control circuit is set as the output of the means for detecting the intensity of the input signal. A digital radio receiver characterized by switching by.