JPH037301B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a data strobe device suitable for reproducing digital data from a digital modulated signal such as a digital FM signal.

[Background of the invention]

As one of the methods of modulating digital signals,
The digital signal is called FM (Frequency).
The digital FM method (also known as the Bi-Phase Mark method) that modulates the frequency modulation (frequency modulation) signal is well known.

In this digital FM system, for example, as described in "Nikkei Electronics" December 1978 issue, page 128, the state inversion interval is set to a minimum of 1/2 of the bit period (T) and a maximum of a bit period (T). It is also characterized by easy clock recovery and data demodulation.

FIG. 1 shows a waveform diagram of the signal obtained by this digital FM method. In the figure, a indicates a serial data string with a signal bit period T, and b indicates a digital FM modulation signal based on this data.

Digital FM as shown in this figure
The method always inverts the state at the data boundary, and for data “1”, the time from the data boundary
This method reverses the state after a delay of 0.5T.
As a result _, as _shown in FIG.
The signal has only two values.

FIG. 2 shows a conventional device for restoring this digital FM signal. Further, FIG. 3 shows waveforms of various parts of the data reproducing circuit of FIG. 2. In addition,
FIG. 3a shows the same serial data as FIG. 1a. In FIG. 2, a digital FM signal transmitted from a transmission source 1 passes through a transmission line 2, is amplified by a regenerative amplifier 3, and is then sent to a regenerative equalizer 4.
The waveform is equalized by This results in a signal as shown in FIG. 3d. Here, the zero points Z ₁ , Z ₂ , . . . of the signal of FIG. 3 d are characterized so as to correspond to the edges E ₁ , E ₂ , . . . of the recorded digital FM signal shown in FIG. 3 c, respectively. Therefore, by limit amplifying the output signal d of the reproduction equalizer 4 using a limiter or a camparator 5, it is possible to restore the digital FM signal e corresponding to the digital transmission signal c, as shown in FIG. 3e. .

However, this restored signal e is affected by intersymbol interference, jitter noise, etc., so re-identification is performed at the waveform center of the 0.5T signal, which is the best identification point of the signal e, and data reproduction is performed. There is a need to.

First, from the restored digital FM signal e, the edge detection circuit 6 extracts edge information as shown in FIG. )
8. PLL (Phase
A locked loop) circuit reproduces the clock as shown in FIG. 3h.

Next, using the rise or fall of the reproduction clock h as a trigger, the restored digital FM
The signal e is re-identified by a strobe circuit 11 composed of a D-flip-flop or the like. As a result, a reproduced digital FM signal i from which effects such as intersymbol interference and jitter noise have been removed can be obtained. The reproduced digital FM signal i is outputted from the output terminal 12 to a digital signal restoration circuit (not shown),
The digital signal is demodulated into an analog signal.
In this example, the rising edge S ₁ of the regenerated clock h,
It is clear from the figure that the strobe circuit 11 is triggered by S ₂ , S ₃ , S ₄ .

The above is a general digital FM method for reproducing data.

In the data reproduction process, one of the factors that greatly affects the bit error rate is the strobe circuit 1.
1 strobe point deviation, that is, the deviation of the rising or falling point of the reproduced clock from the waveform center point of the 0.5T signal of the restored digital FM signal e.

Now, as an example, the bit period T of the digital signal
is T≒172ns, that is, the data transmission rate
Figure 4 shows the bit error rate vs. strobe point deviation characteristics in the case of 5.8 Mbit/s. Here, since the data transmission rate of the digital signal is 5.8 Mbit/s, the clock frequency of the digital FM system is 11.6 MHz, and the possible range of the strobe point deviation is approximately ±43.1 ns.

As is clear from Figure 4, if the strobe point deviates by ±10 ns from the best discrimination point, the error rate will be approximately 1.
It gets worse by orders of magnitude. Therefore, it is necessary to suppress the strobe point deviation to zero as much as possible.

To do so, complicated adjustments must be made for each device, which poses a problem of high adjustment costs. Another problem is that it is extremely difficult to compensate for temperature characteristics and aging.

To solve the above drawbacks, it is necessary to automatically correct the strobe points. To automatically correct the strobe points,
Point deviation information is required.

Now, in the data reproducing circuit shown in Fig. 2,
If the strobe point deviates from the best discrimination point (the center point of the 0.5T signal) by ΔT, the output signal of the strobe circuit 11, that is, the reproduced digital
The FM signal has a waveform shown in FIG. 5k for the input signal waveform e. Here, FIG. 5j shows a clock in which the optimum strobe point is shifted by ΔT.

From this waveform k, the reproduced digital FM signal is
It turns out that it has strobe point information, and this strobe point information, that is,
The amount of phase deviation from the best discrimination point is determined by the exclusive OR of the input and output signals of the strobe circuit 11.
OR, hereinafter abbreviated as Ex-OR. ) can be obtained by taking FIG. 5m shows the output of Ex-OR and represents the amount of phase deviation in terms of pulse width.

Here, if the amount of phase deviation, that is, the pulse width is Δθ, the best discrimination point is the center of the 0.5T signal, so it can be expressed as Δθ=1/4T−ΔT (1).

However, as is clear from Figure 5m,
In the case of the digital FM system, the number of data D ₁ , D ₂ . . . representing the amount of phase deviation changes depending on the ratio of "0" to "1" of recorded data. When the proportion of "1" is high, the number of phase deviation amount data is large, and when the proportion of "0" is large, the number of data is small.

Therefore, the relationship between the strobe point deviation information amount and the integral value of the phase deviation amount differs depending on the transmitted data, as shown in FIG. In FIG. 6, a indicates a case where the transmitted data is all "1", and b indicates a case where the data is all "0". In general,
Since the data contains a mixture of “1” and “0”,
The amount of phase deviation will take a value between a and b.

It is clear from FIG. 6 that even if the strobe point is at the best discrimination point (the center of the 0.5T signal), the amount of phase deviation obtained is not constant. Therefore, if the amount of phase deviation obtained from the Ex-OR output of the input/output signal of the strobe circuit 11 is simply integrated to obtain strobe point deviation information, the deviation information will include information on the transmission data string. become. Therefore, if the previous phase deviation amount is integrated in its original form, it is impossible to use it as a strobe point correction control signal.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a data strobe device that can solve the above problems, automatically correct deviations in strobe points, and reduce error rates.

[Summary of the invention]

The present invention includes a clock generation means for generating a clock signal based on a digital modulation signal whose state inversion interval changes according to the digital signal, a phase control means for controlling the phase of the clock signal, and an output from the phase control means. strobe means for reproducing the digital modulation signal based on the phase-controlled clock signal,
The phase control means includes a first exclusive OR means for taking an exclusive OR of the digital modulation signal inputted to the strobe means and a reproduced signal outputted from the strobe means; Another strobe means for data reproduction performs an exclusive OR of the reproduced signal and the output signal of the other strobe means based on a signal obtained by inverting the clock signal outputted from the phase control means. and a clock control reference signal generating means for generating a clock control reference signal; and a strobe point control means for controlling the strobe point, thereby automatically correcting strobe point deviations.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 7 and 8. Here, FIG. 8 is a waveform diagram of each part of FIG. 7.

Note that this embodiment has parts common to the data strobe device shown in FIG. 2 above. Therefore, these common parts are given the same reference numerals. Further, since the functions and operations of the common parts are as described in FIG. 2, detailed explanations will be omitted.

In FIG. 7, a digital FM signal transmitted from a transmission source 1 passes through a transmission path 2, and then
The signal is amplified by a regenerative amplifier 3 and waveform-equalized by a regenerative equalizer 4. When the output signal of the reproduction equalizer 4 is amplified by the limiter or comparator 5, the digital signal shown in Fig. 8e is obtained.
FM signal can be restored.

However, the restored digital FM signal e is
It is affected by intersymbol interference, jitter noise, etc.
It is necessary to perform data reproduction. Therefore, the output signal e of the comparator 5 is sent to the edge detection circuit 6.
Enter it to retrieve the edge information. Thereafter, based on this edge information, a PLL circuit consisting of a phase detector 7, a voltage controlled oscillator (VCO) 8, and a loop filter 9 performs clock regeneration. This recovered clock is input to a clock phase shift circuit 10, and the phase is controlled so that the rising point of the recovered clock is at the best discrimination point for data recovery, that is, the center of the 0.5T signal.

This phase shift control signal is obtained as follows. now,
The rising point of the regenerated clock, that is, the strobe
Assuming that the point is deviated from the best discrimination point as shown in FIG.
Obtained as the output of Ex-OR16. The phase deviation signal waveform representing the amount of phase deviation is shown in FIG. 8r.

Further, a reference signal for phase control that changes according to the data described above is obtained by a circuit including a strobe circuit 15, an inverter 17, and an Ex-OR 18. That is, the strobe circuit 15 outputs a signal s obtained by delaying the data output signal k by T/4.
is obtained, and by taking the exclusive OR of the data signal s delayed by T/4 by Ex-OR18 and the undelayed data signal k, which is the input signal of the strobe circuit 15, the best discrimination point is found. Show T/
Four width pulses can be obtained corresponding to the data. Waveform t is the control reference signal obtained by the circuit described above.

The phase deviation amount r and the control reference signal t are integrated by integration circuits 19 and 20, respectively, and then input to the clock phase shift control circuit 10 as a phase shift control signal. The clock phase shift control circuit 10 is automatically controlled using the difference between the integral values output from the integration circuits 19 and 20. Note that by controlling based on the difference in integral values, the information components of the data string can be canceled out, and the information components of the data string can be prevented from being included in the phase shift control signal. This clock phase shift control circuit 10 is based on the ``data reproducing device'' (patent application filed in 1983-1989), which the inventors of the present invention previously applied for.
227105) etc. can be used.

The strobe point deviation of the clock output from the PLL circuit is corrected by the thus obtained phase shift control signal. The strobe circuit 11 is triggered by the clock with this strobe point deviation corrected, and the output terminal 12 reduces the error rate and eliminates intersymbol interference.
Digital data from which the effects of jitter, noise, etc. have been removed.
FM signal is output.

As is clear from the above description, according to this embodiment, the clock phase shift circuit is controlled by the control reference signal t and the phase deviation signal r according to the data, so that the clock phase shift circuit is controlled by the control reference signal t and the phase deviation signal r. PLL due to impact
Strobe point deviations that are caused by oscillation frequency deviations of the circuit's voltage-controlled oscillator and cannot be corrected by initial fixed adjustment can be removed very effectively.

Furthermore, since the clock phase shift control signal obtained in this embodiment is obtained by integrating the phase deviation signal r and the control reference signal t, it has the characteristic that it is not easily affected even if a data error occurs. .

Furthermore, in this embodiment, the clock phase shift circuit is controlled by integrating the control reference signal t and the phase deviation signal r according to the data and taking the difference, so that the timing of the data strobe is can be optimally controlled, and the error rate of digital signal reproduction can be significantly reduced.

The basic concept of the present invention is to correct the timing of the data strobe by changing the reference signal for phase shift control according to the data of the digital FM signal. However, it is clear that there is no problem.

Also, digital FM signal has data time interval
The circuit configuration shown in the above embodiment can also be applied to a signal in which a 1.5T width signal different from 0.5T and T is added as a synchronization signal to make it easier to identify the synchronization signal, and the effectiveness of the present invention is does not change.

Furthermore, it goes without saying that the effects of this embodiment do not depend on the characteristics of the digital FM signal transmission path itself, and are effective for any transmission path.

〔Effect of the invention〕

As described above, according to the present invention, the strobe can be used without depending on the transmission data string of the digital signal, without requiring complicated adjustment, and without being affected by temperature characteristics or aging. Point deviations can be automatically corrected. Furthermore, the reproduced data error rate can be significantly reduced. Furthermore, the present invention can be realized with an inexpensive and simple circuit configuration.

[Brief explanation of the drawing]

Figure 1 is a waveform diagram to explain the digital FM signal, Figure 2 is a block diagram showing an example of a conventional reproducing circuit, Figure 3 is a waveform diagram of the signals of each part in Figure 2, and Figure 4 is a strobe.・A diagram showing an example of point deviation versus bit error rate. Figure 5 is a waveform diagram to explain the signal waveform when triggered by a clock with the optimum point of the strobe point shifted. Figure 6 is a waveform diagram to explain the signal waveform when the optimal point of the strobe point is shifted. FIG. 7 is a block diagram showing an embodiment of the present invention, and FIG.
The figure is a waveform diagram of signals at various parts in FIG. 7. Explanation of symbols, 10... Clock phase shift circuit, 1
1, 15... strobe circuit, 19, 20... integral circuit.

Claims (1)

[Scope of Claims] 1. A clock generating means for generating a clock signal based on a digital modulation signal whose state inversion interval changes according to the digital signal; a phase control means for controlling the phase of the clock signal; and a phase control means for controlling the phase of the clock signal. strobe means for reproducing the digital modulation signal based on a phase-controlled clock signal output from the strobe means; a first exclusive OR means for exclusive ORing the reproduction signal output from the strobe means, based on a signal obtained by inverting the clock signal output from the phase control means; another strobe means for reproducing data; a clock control reference signal generating means for generating a clock control reference signal by performing an exclusive OR of the reproduction signal and the output signal of the other strobe means; and strobe point control means for controlling the phase of a clock signal according to the difference between the output signal of the digital OR means and the output signal of the clock control reference signal generation means. 2. The strobe point control means has an integrating circuit that integrates the output signal of the first exclusive OR means and the output signal of the clock control reference signal generating means, and integrates the integrated outputs from the two integrating circuits. 2. The data strobe device according to claim 1, wherein the phase of said clock signal is controlled in accordance with the difference.