JPH0787471B2 - Digital radio receiver - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital radio receiver for receiving a signal that has been angle-modulated by a signal such as digitized voice, data, etc., and more specifically, in demodulating the digital signal. ,
The present invention relates to a digital radio receiver capable of stably determining 1,0 of a demodulated signal by removing a DC component that changes due to fluctuations in carrier frequency and center frequency of a frequency discriminator.

[Conventional example] Conventionally, in this kind of digital FM radio receiver, an angle-modulated signal is demodulated from a received carrier wave, and a digital signal is restored from the demodulated signal.

In FIG. 2, an example of which is shown, a signal angle-modulated by signals such as digitized voice and data is input to a frequency converter 2 via an antenna 1. The received signal is converted into an intermediate frequency signal by the frequency converter 2 at the oscillation frequency of the local oscillator 3, and a predetermined frequency band of the intermediate frequency signal is passed by the band pass filter 4. The frequency discriminator 5 demodulates the angle-modulated signal from the intermediate frequency signal in the predetermined frequency band, and the low-pass filter 6 removes noise from the demodulated signal. Digital signals such as voice and data are restored from the modulated signal from which noise has been removed by the identification / judgment device 7 in synchronization with the clock signal generated by the clock recovery circuit 8. At this time, the low-pass filter 9 determines "1" or "0" of the demodulated signal, and detects the DC component ΔV that changes due to the fluctuation of the carrier frequency and the center frequency of the frequency discriminator 5, When the digital signal is restored by the discrimination / determination unit 7, correction is performed according to the variation. That is, in the discrimination / determination unit 7, the restoration error of the digital signal is corrected by changing the reference voltage for determining "1" or "0" of the demodulated signal according to the change in the restoration.

[Problems to be Solved by the Invention] By the way, as a method of discriminating a digital signal in the discriminating / determining unit 7 of the digital radio receiver, the discrimination level is set to one and "1 It is a method of judging "," 0 ", or a method of judging" 1 "or" 0 "based on a discrimination level of binary, quaternary or higher values which is generally called multi-value judgment. 4 of them
Judgment of "1" and "0" by the value discrimination method is extremely accurate, but it is necessary to set four discrimination levels, and depending on the judgment of the discrimination level, there is an error in the judgment of "1" and "0". Therefore, it is necessary to pay close attention to the adjustment of the set value. Further, in these methods, it is also important for the determination accuracy of “1” and “0” that the input signal does not fluctuate up and down with respect to the reference voltage of the discrimination level.

However, in the above digital radio receiver,
Since the reference voltage of the discrimination / determination unit 7 is changed according to the DC component detected by the low-pass filter 9, “1”,
There is a problem that the determination operation of "0" tends to be unstable.

Further, in order to improve the frequency characteristic according to the input signal, if the cutoff frequency of the low pass filter 9 is increased,
The detected variation changes according to the distribution state of the received signal, and the reference voltage changes accordingly, which makes the identification of "1" and "0" unstable. is there. Furthermore, if the cutoff frequency is lowered, the timing of detecting the fluctuation is delayed (because the rise time of reception becomes long), so similarly, "1",
The identification judgment of "0" becomes unstable.

Therefore, a method of variably controlling the cutoff frequency of the low-pass filter 9 in accordance with the input signal is conceivable. Especially, in the multi-valued discrimination method, the circuit configuration becomes complicated and the determination operation becomes unstable. It also causes a cause.

As described above, in any case, when the DC component included in the demodulated signal changes, the reference voltage in the discrimination / determination unit 7 changes, so that the discrimination determination of “1” or “0” may become unstable. .

The present invention has been made in view of the above problems, and an object thereof is to remove the DC component of the demodulated signal in the preceding stage of the discrimination judgment of "1" and "0", thereby making it possible to reduce the frequency of the carrier wave and the frequency discriminator. It is an object of the present invention to provide a digital radio receiver capable of accurately performing digital identification, even if the center frequency fluctuates, and performing the identification determination stably.

[Means for Solving the Problems] In order to achieve the above object, the structural features of the present invention are as follows.
An antenna receives a carrier wave that has been angle-modulated by signals such as digitized voice and data, the frequency discriminator demodulates the angle-modulated signal, and the discriminator determines the demodulated signal "1" or "0". A low-pass filter for detecting a DC component contained in the demodulated signal between the frequency discriminator and the discriminator / discriminator in a digital radio receiver for judging and restoring the signals such as the digitized voice and data. A filter and a subtractor composed of a differential amplifier circuit, into which the DC component detected by the low-pass filter is input to one input terminal and the demodulated signal is input to the other input terminal, are connected, and The DC component which changes due to fluctuations in the frequency of the carrier wave and the center frequency of the frequency discriminator is removed from the demodulated signal before being input to the discrimination / determination unit.

[Operation] With the above configuration, the DC component of the demodulated signal of the digitized voice and data obtained from the carrier wave is subtracted by the subtractor of the DC component subtracting means before the demodulated signal is input to the discrimination / determination unit. (Differential amplifier circuit) is subtracted. That is,
When the digital signal is restored from the demodulated signal, the DC component of the demodulated signal is removed, so the reference voltage for "1", "0" discrimination judgment is the frequency of the carrier wave and the center frequency of the frequency discriminator. The operation of the "1" and "0" discrimination determination is stably performed without being influenced by the fluctuation of.

[Examples] Examples of the present invention will be described below with reference to FIG.
In the figure, the same parts as those in FIG.

In the figure, the demodulated signal from which noise has been removed by the low-pass filter 6 is input to a low-pass filter 10 that has the same function as the low-pass filter 9 of FIG. ) Is input to the inverting input terminal of the differential amplifier circuit 11. The direct-current component ΔV changed by the fluctuation of the carrier frequency detected by the low-pass filter 10 and the center frequency of the frequency discriminator 5 is input to the non-inverting input terminal of the differential amplifier circuit 11. That is, the DC component of the demodulated signal output from the low pass filter 6 is subtracted by the differential amplifier circuit 11. In this way, the demodulated signal from which the influence of the above fluctuation is removed is input to the discrimination / determination unit 7 and the clock generation circuit 8.

Next, the circuit operation of the digital radio receiver will be described.

First, the carrier wave transmitted from the transmitter is received by the antenna 1, and the frequency discriminator 5 demodulates the angle-modulated signal of the carrier wave. The demodulated signal (signal such as voice / data) is noise-removed by the low pass filter 6, and then input to the low pass filter 10 and the inverting input terminal of the differential amplifier circuit 11. At this time, when the frequency of the received carrier wave and the center frequency of the frequency discriminator 5 are fluctuated, the DC component ΔV which changes due to the fluctuation is detected by the low-pass filter 10, and the DC component ΔV is differentiated. The signal is input to the non-inverting input terminal of the amplifier circuit 11, and the differential amplifier circuit 11 performs difference calculation processing between the demodulated signal and its DC component ΔV. That is, since the DC component ΔV contained in the demodulated signal is removed in the differential amplifier circuit 11, this differential amplifier circuit 11
The demodulated signal passed through 11 is always constant in terms of direct current.

In this way, since the demodulated signal that is DC-constant is input to the discrimination / determination unit 7, the reference voltages for the discrimination determination of “1” and “0” in this discrimination / determination unit 7 are always set to be constant. Therefore, it is not necessary to change, and the unstable operation of the identification determination due to the change of the reference voltage as in the past is eliminated. In addition, even if the cutoff frequency of the low-pass filter 10 is increased to improve the frequency characteristic, it does not affect the reference voltage in the discrimination / determination unit 7, so that "1", "0"
The identification determination operation of is stably performed.

[Effects of the Invention] As described above, according to the digital radio receiver of the present invention, a DC component is subtracted when a carrier wave which is angle-modulated by digitized voice, a data signal, etc. is received and the signal is demodulated. Since the demodulation signal passed through this subtractor is provided with a "1" or "0" discrimination determination to obtain the digital signals such as the voice and data, the carrier frequency and the frequency discriminator intermediate When the frequency fluctuates, since the DC component that changes due to the fluctuation is removed by the subtractor, the demodulated signal to be discriminated and judged is always DC constant, and it is not necessary to change the reference voltage for discrimination and judgment. There is an effect that the determination operation of 1,0 is stably and accurately performed.

[Brief description of drawings]

FIG. 1 is a schematic partial block diagram of a digital FM radio receiver showing an embodiment of the present invention, and FIG. 2 is a schematic partial block diagram of a conventional digital radio receiver. In the figure, 1 is an antenna, 2 is a frequency converter, 3 is a local oscillator, 4 is a bandpass filter, 5 is a frequency discriminator, 6 is a low-pass filter (for noise removal), 7 is an identification / determination unit, and 8 is A clock recovery circuit, 9 and 10 are low-pass filters (DC component detecting means), and 11 is a subtractor (DC component subtracting means).

Claims (1)

[Claims] 1. A carrier that is angle-modulated by a signal such as digitized voice or data is received by an antenna, the angle-modulated signal is demodulated by a frequency discriminator, and "1" of the demodulated signal is discriminated by an identification judging device. , "0" and restores the digitized voice, data, etc. signals. In the digital radio receiver, the DC component contained in the demodulated signal is inserted between the frequency discriminator and the discrimination determiner. A low-pass filter for detection, and a subtractor consisting of a differential amplifier circuit in which the DC component detected by the low-pass filter is input to one input terminal and the demodulated signal is input to the other input terminal. Connect
Digital radio reception, characterized in that, before inputting to the discrimination / determination unit, a DC component that changes due to fluctuations in the frequency of the carrier wave and the center frequency of the frequency discriminator is removed from the demodulated signal. Machine.