Miscellaneous active electrical nonlinear devices – circuits – and – Specific signal discriminating without subsequent control – By amplitude
Reexamination Certificate
2000-03-24
2001-08-07
Tran, Toan (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific signal discriminating without subsequent control
By amplitude
C327S074000
Reexamination Certificate
active
06271690
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to discriminators and, more specifically, to a discriminator automatically generating optimum thresholds and discriminating the amplitude of an input multi-level signal with the generated thresholds.
2. Description of the Background Art
Conventionally, a multi-level signal varying in amplitude among three or more values can be sent and received in a transmission system. In such multi-level signal, information is assigned to each amplitude value. The receiving side in the transmission system discriminates the amplitude of the received multi-level signal using predetermined thresholds. However, with fluctuations in amplitude of the multi-level signal due to various factors, fixed thresholds are not preferable because each of the thresholds may be shifted from a mid-level between one amplitude value and the amplitude value just one level below or above. As a result, the receiving side may perform erroneous amplitude discrimination, or the resultant pulse width after discrimination may be distorted.
Furthermore, in a transmission system of a binary signal indicative of “Hi” or “Lo”, the receiving side may perform amplitude discrimination with a discriminator CD as shown in FIG.
12
. In
FIG. 12
, the discriminator CD is adapted to automatically generate a threshold that is appropriate for amplitude discrimination (so-called automatic threshold control) even if the amplitude of the received binary signal may fluctuate. The discriminator CD includes an input terminal
21
, a branching part
22
, a peak detector
23
, a base level generator
24
, a threshold generator
25
, and a comparator
26
.
The branching part
22
branches a binary signal fed through the input terminal
21
into two, outputting one to the peak detector
23
and the other to the comparator
26
. The peak detector
23
detects and holds a peak value of the received binary signal. The detected peak value is equal in electric potential to “Hi” of the binary signal which may fluctuate, and fed to the threshold generator
25
. The base level generator
24
generates a base level equal in electric potential to “Lo” of the binary signal, and outputs the base level to the threshold generator
25
. The threshold generator
25
generates a threshold having a mid-level between the received peak level and base level, and outputs the threshold to the comparator
26
. The comparator
26
compares the amplitude of the branched binary signal with the threshold, and outputs the comparison result. As such, the peak detector
23
detects the peak value of the binary signal, enabling the threshold generator
25
to automatically generate the threshold even with fluctuations in amplitude of the binary signal.
For applying the above discriminator CD to multi-level signal transmission systems, the threshold generator
25
, which generates the mid-level value, is modified to generate a plurality of thresholds each having a mid-level between one amplitude value and the amplitude value just one level below or above of a multi-level signal.
In general, a marking ratio of appearing each amplitude value of a multi-level signal is lower than that of a binary signal. Therefore, the maximum amplitude value of the multi-level signal does not necessarily appear during an interval defined by a time constant of the peak detector
23
. In such case, the peak value detected by the peak detector
23
does not become equal in electric potential to the maximum amplitude value of the multi-level signal. As a result, the threshold generator
25
cannot generate accurate thresholds.
Furthermore, the marking ratio in the multi-level signal is difficult to manage compared with that in the binary signal. In addition, the mean value of the multi-level signal does not necessarily indicate the mid-level of the amplitude. Therefore, replacing the peak detector
23
with a mean value detector is not practical.
Due to the above background, in conventional multi-level signal transmission systems, the transmitting side is required to transmit at least a maximum amplitude value of the multi-level signal (and a minimum amplitude value thereof as required) to the receiving side every predetermined time to charge a capacitance of the peak detector
23
. Or, the transmitting side is required to produce a multi-level signal in which at least its maximum amplitude value (and also minimum amplitude value, in some cases) moderately appears. Therefore, when the conventional discriminator CD is applied to a multi-level signal transmission system, the transmitting side is disadvantageously under restrictions on generating a multi-level signal.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide a discriminator enabling a transmitting side to generate a multi-level signal with less restrictions.
The present invention has the following aspects to achieve the above object. Further, each aspect has technical effects as described below.
A first aspect of the present invention is directed to a discriminator discriminating a multi-level signal varying in amplitude among three or more values, comprising: a first branching part branching the multi-level signal externally inputted thereto into two; a wave-shaping circuit shaping a waveform of the multi-level signal branched by the first branching part under a predetermined condition; a detector detecting a first reference level based on an output signal from the wave-shaping circuit; a reference level generator generating a second reference level of the multi-level signal externally inputted; a threshold generator generating a required number of thresholds according to the first and second reference levels; a comparing circuit comparing the amplitude of the multi-level signal branched by the first branching part with the thresholds generated by the threshold generator; and a control signal generator generating a control signal according to a comparison result by the comparing circuit, the wave-shaping circuit shaping the waveform of the multi-level signal inputted thereto according to the control signal outputted from the control signal generator so that the detector can correctly detect the first reference level.
According to a second aspect, in the first aspect, the threshold generator generates (the number of amplitude values−1) different thresholds according to the first and second reference levels, the comparing circuit comprises: a second branching part branching the multi-level signal inputted thereto into (the number of amplitude values−1); and (the number of amplitude values−1) comparators each receiving different one of the thresholds generated by the threshold generator and the multi-level signal branched by the second branching part, and each of the comparators compares the amplitude of the received multi-level signal with the received threshold.
In the first and second aspects, even when the discriminator is provided with a multi-level signal in which one or more specific amplitude values are excessively distributed during a time interval, the wave-shaping circuit can perform wave-shaping according to the control signal. Therefore, the comparing circuit can discriminate the amplitude of the multi-level signal using correct thresholds. This amplitude discrimination enables generation of the multi-level signal in the transmitting side with less restrictions.
According to a third aspect, in the first aspect, the discriminator further comprises an amplitude adjuster adjusting a relative difference between the amplitude of the multi-level signal branched by the first branching part and each of the thresholds generated by the threshold generator.
In the third aspect, the amplitude adjuster adjusts the relative difference between the amplitude of the multi-level signal and the thresholds. The threshold generator can thus generate more appropriate thresholds, thereby greatly reducing the possibility of generating erroneous discrimination results and further avoiding pulse-width distortion in the di
Furusawa Satoshi
Hirano Jun
Morikura Susumu
Matsushita Electric - Industrial Co., Ltd.
Tran Toan
Wenderoth , Lind & Ponack, L.L.P.
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