JPS5826211B2 - Digital signal reproduction method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a digital signal regeneration method for stably shaping the waveform of a digital signal whose quality is largely degraded due to the frequency characteristics of a transmission system.

In a transmission system or a recording system, there is generally a deterioration in frequency characteristics, etc., and if this is significant, it is difficult to reproduce the same correct "1" and "0" sequence as the original signal even in a digital signal.

As an example of this, consider an NRZ format digital signal received via a transmission system having frequency characteristics as shown in FIG.

The frequency f corresponds to 1/2 of the transmission lock frequency.

FIG. 2 shows the waveforms of the original signal a and the received signal S at this time.

As is clear from the figure, the deterioration of the amplitude is relatively small in areas where there are few changes in "1" and 0, but the amplitude gradually decreases in areas with large changes, that is, parts with high spectra. The amplitude suffers the most attenuation where the inversion of O'' occurs at the clock rate.

When such a received signal is supplied to a discrimination circuit having a threshold level between "1" and "0", "1" and "0" are detected.
Since the signal amplitude is large in the part where "0" is less inverted, even if the signal contains noise, it can be separated.

However, as the number of inversions of n 1 tt,0'' increases, the signal amplitude decreases, so the possibility of erroneous determination due to noise increases.

Furthermore, even if discrimination is possible, the variation in the inversion position of the reproduced signal becomes large, resulting in an error.

In order to improve this, an equalization method has conventionally been used in which a transversal filter is used to inversely correct the frequency characteristics of the transmission system and recording system.

However, this type of system has the disadvantage that the circuit structure is complicated and expensive, and it is generally difficult to handle.

SUMMARY OF THE INVENTION An object of the present invention is to provide a digital signal reproducing method which eliminates the above-mentioned drawbacks and can accurately and stably extract digital signals with a simple configuration.

To accurately reproduce the original signal from the received digital signal,
It is necessary that the rise of the inverted portion of the digital signal be sharp, and that the amplitude of the portion where the inversion is severe, that is, the portion where there are many high frequency components, is not small.

Therefore, according to the present invention, a digital signal received at a predetermined clock rate frequency is supplied to a low Q band pass filter (B P F) having a center frequency approximately half the clock rate frequency, The amplitude of this output signal is amplified and adjusted, and then added to the digital signal.

This addition signal has a sharp change in the inversion section and an almost uniform amplitude as a whole, so stable level judgment can be performed by supplying this signal to a level discriminator and shaping the waveform. .

FIG. 3 is a diagram showing an embodiment of the present invention.

Reference numeral 10 is a receiving terminal for receiving and receiving digital signals from a transmission system or a recording system.

This digital signal is passed through a band pass filter (BPF) 11
and is supplied to the adder 12.

BPFl 1 has a center frequency that is approximately 1/2 of the clock rate frequency in the transmission system or recording system, and the vicinity of this frequency can be extracted as is.

The output signal of BPFl 1 is supplied to adder 12 after its amplitude is amplified and adjusted via amplifier 13 .

Adder 12 adds the output signal of amplifier 13 to the human input digital signal.

This added signal is supplied to a level discriminator 14 for level determination, and its output is output from a terminal 15 as a reproduced digital signal.

FIG. 4 is a waveform diagram showing the operation of the embodiment shown in FIG. 3.

3A shows the original signal, and FIG. 3 shows the received signal received at the terminal 10 via a transmission system or recording system not shown in FIG. 3B.

At this time, the output signal of BPFl 1 includes a frequency component of approximately 1/2 of the clock rate frequency, as shown in FIG.

d in the figure is the output signal of the adder 12, in which the change in the inversion section is rapid and the amplitude as a whole is almost uniform.

Figure d shows the reproduced digital signal obtained at the terminal 15 when discrimination is made at the threshold level shown in figure C.

The output waveform of BPFI 1 will be explained in more detail.

If we consider now that the input signal is inverted from a non-inverted state, this is equivalent to adding a step signal as shown in FIG. 5a to BPFI 1.

The output signal of BPFl 1 at this time has a ringing waveform that decreases exponentially as shown in the figure.

Here, the ringing amplitude is approximate. -ca f o t, and the frequency of vibration is f unless Q is extremely small.

(center frequency of BPFll). Since the first transient of this ringing (indicated by reference numeral 17) is in the direction of change of the input signal, it can be used as an edge correction signal (to sharpen the change of the inversion part).

However, the second transient (indicated by 18)
is in the opposite direction to the direction of change of the input signal, so if the next input signal does not change, the amplitude of the signal will be narrowed, so this must be kept as low as possible.

The ratio of the magnitude of the second transient to the first transient is.

- This ratio is 50%, 30%, 20%.
.

If it is 10%, Q is 2.0 and 1.3, respectively.
゜0.8, 0.68.

Generally, when Q is larger than this, the second transient becomes large and cannot be used as an effective correction signal.

By the way, since the amplitude of a portion of the input signal of the BPF that is strongly inverted is small, the output signal of the BPF also has a small amplitude of that portion.

On the other hand, there is generally a desired signal level for a level discriminator, and if you increase the amplitude of the heavily inverted part to this level,
Ringing increases in areas with little reversal.

Therefore, the second transient naturally also becomes larger.

Furthermore, since the ringing frequency changes slightly depending on the Q value, the center frequency of the BPF and the Q value should be appropriately selected in consideration of this.

As mentioned above, the value of Q is up to a height of 2.0, and according to the results of experiments, around 0.63 is optimal.

An example of the configuration of such a PF is shown in FIG.

This uses a parallel resonant circuit.

The above embodiment shows a case where the characteristics of the transmission system or the recording system are fixed, and the output signal of the BPF 11 is amplified and adjusted to a desired signal level by the amplifier 13 whose gain is preset.

FIG. 7 shows another embodiment of the present invention suitable for cases where there are variations in the characteristics of the transmission system or recording system.

The input digital signal is supplied to an automatic gain control circuit 21 to keep the amplitude of the low frequency component constant.

The output signal of the automatic gain control circuit 21 is supplied to the first BPF 22 and the edge portion is extracted.

The output signal of the BPF 22 is supplied to an adder 24 via an amplifier circuit 23 whose gain is controllable.

The adder 24 adds the output signal of the automatic gain control circuit 21 and the output signal of the amplifier circuit 23 and supplies the result to the level discriminator 25.

Further, the addition signal obtained by the adder 24 is added to the second BP
The signal is supplied to the peak detection circuit 27 via F26.

The peak detection circuit 27 performs peak detection on the output signal of the BPF 26 and supplies its DC output as a gain control signal to the amplifier circuit 23 .

The Q of the second BPF Z6 does not need to be as small as the Q of the first BPF 22.

Also, the automatic gain control circuit 21 uses a gain-controllable amplifier like the latter stage of the BPF 22, and after removing high frequency components from the output through an LPF, controls the gain of the amplifier using the DC output obtained by peak detection. It can also be configured as follows.

FIG. 8 shows yet another embodiment of the invention.

The input signal is passed through an automatic gain control circuit 31 to keep the amplitude of the low frequency component constant.

The edge portion of the output signal of the automatic gain control circuit 31 is extracted via the BPF 32.

The output signal of the BPF 32 is adjusted to a substantially constant amplitude by an automatic gain control circuit 33 and supplied to an adder 34.

Further, the output signal of the automatic gain control circuit 31 is supplied to the adder 34 via a band-elimination filter (BEF) 35 that removes frequencies around 1/2 of the clock rate frequency.

The level of the added signal output from the adder 34 is determined by a level discriminator 36.

As described in detail above, according to the present invention, fluctuations in the received waveform due to the frequency characteristics of the transmission system or recording system can be corrected, data separation can be performed stably and reliably, and the system is resistant to noise.

Furthermore, even if the frequency characteristics of the transmission system or recording system change, it can be automatically corrected.

Furthermore, the circuit configuration is simpler than that of the prior art, and an inexpensive device can be provided.

[Brief explanation of drawings]

Figure 1 is a diagram showing the frequency characteristics of the transmission system, Figures 2a and b are diagrams showing the original signal and received signal when the transmission system shown in Figure 1 is used, and Figure 3 is one embodiment of the present invention. Illustration showing an example, 4th
Figures ``a''-e are waveform diagrams for explaining the operation of the embodiment shown in Figure 3, Figure 5a, Figures b and 6 are BPF used in an embodiment of the present invention.
Figures 7 and 8 are diagrams showing other embodiments of the present invention. 11...BPF, 12...Adder, 13...Amplifier, 14...Level discriminator.

Claims (1)

[Claims] 1. A digital signal received at a predetermined clock rate frequency is supplied to a bandpass filter whose center frequency is approximately 1/2 of the clock rate frequency, and the amplitude of the output signal of the bandpass filter is amplified. A digital signal reproducing method characterized in that the added signal is waveform-shaped by a level discriminator.