Modulators – Amplitude modulator – Plural modulation
Reexamination Certificate
1998-08-05
2001-03-27
Kinkead, Arnold (Department: 2817)
Modulators
Amplitude modulator
Plural modulation
C332S155000, C332S161000, C332S159000, C332S115000, C375S320000
Reexamination Certificate
active
06208217
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ASK modulator and more particularly to an ASK modulator which intermits a carrier signal to be transmitted to generate an ASK modulated signal by turning ON and OFF a switching element for transmitting the carrier signal depending on the logical level of a digital signal.
2. Description of the Related Art
In the typical one of the ASK modulator to generate an ASK modulated signal, the ASK modulated signal can be obtained at the other end of a switching diode by connecting in series a switching diode to a carrier signal transmission path, supplying both carrier signal and digital signal to one end of the switching diode, transmitting the digital signal by turning ON the switching diode when the digital signal is in a logical high level and rejecting transmission of the digital signal by turning OFF the switching diode when the digital signal is in a logical low level.
Here,
FIG. 3
is a circuit diagram showing an example of the structure of the ASK modulator of the related art as explained above.
As shown in
FIG. 3
, an ASK modulator comprises a switching diode
21
, a first coupling capacitor
25
connected in series between one end (input end) of the switching diode
21
and a carrier signal input end
27
, a current limiting resistor
24
and a first choke coil
22
for rejecting a higher frequency signal connected in series between one end of the switching diode
21
and the digital signal input end
29
, a second choke coil
23
for rejecting a higher frequency signal connected between the other end (output end) of the switching diode
21
and the ground point and a second coupling capacitor
26
connected in series between the other end of the switching diode
21
and the ASK modulated signal output end
28
.
The ASK modulator of the structure explained above operates as explained below.
To the carrier signal input end
27
, a carrier signal is supplied, while to the digital signal input end
29
, a digital signal, which changes between the logical high level (as this level, a voltage level, for example 5 V, which is higher than 0.7 V indicating a voltage drop in the forward direction of the switching diode
21
, is selected) and the logical low level (as this level, a voltage level, for example 0 V, which is lower than 0.7 V indicating a voltage drop in the forward direction of the switching diode
21
, is selected).
When the digital signal supplied to the digital signal input end
29
is in the logical high level, such the logical high level signal flows to the ground point from the digital signal input end
29
via the current limiting resistor
24
, the first choke coil
22
, the switching diode
21
and the second choke coil
23
to turn ON the switching diode
21
. Therefore, the carrier signal supplied to the carrier signal input end
27
is transferred to the ASK modulated signal output end
28
via the first coupling capacitor
25
, the switching diode
21
and the second coupling capacitor
26
.
Meanwhile, when the digital signal supplied to the digital signal input end
29
changes to the logical low level signal, this logical low level signal becomes almost equal to the ground potential and thereby voltages at both ends of the switching diode
21
become equal to each other to turn OFF the switching diode
21
. Therefore, the carrier signal supplied to the carrier signal input end
27
is rejected to be transferred by the switching diode
21
. As a result, it is not transferred to the ASK modulated signal output end
28
.
As explained above, the switching diode
21
shifts to ON or OFF state to transmit the carrier signal or reject transmission thereof as the digital signal to shift to the logical high level or the logical low level. Therefore, the ASK modulated signal in which the carrier signal is intermitted can be output from the ASK modulated signal output end
28
.
The ASK modulator of the related art explained previously generates a ringing phenomenon in which the shifted logical low level changes in the high and low direction within the short period immediately after the change in the digital signal from the logical high level to the logical low level.
FIG. 4
is a characteristic diagram showing the relationship between the ringing phenomenon generating condition and the switching level when the digital signal changes to the logical low level from the logical high level in the ASK modulator of the related art.
In
FIG. 4
, the signal level is plotted on the vertical axis, the time on the horizontal axis, a solid line indicates the level changing condition of the digital signal supplied to the digital signal input end
29
(almost equal to the level changing condition of the digital signal supplied to the input end of the switching diode
21
), and a chain line (phantom line) indicates the switching level of the switching diode
21
, here, equal to a voltage drop in the forward direction of the switching diode
21
.
As indicated by a solid line in
FIG. 4
, when the digital signal changes from the logical high level to the logical low level, the logical low level of the digital signal shows, immediately after such level change, variation of level in the high and low direction within a short period of time. When the time passes, such level variation becomes small, generating the ringing phenomenon which is converted to the logical low level. When level variation due to this ringing phenomenon is large, the logical low level of the digital signal supplied to the input end of the switching diode
21
exceeds, immediately after the change of digital signal to the logical low level, once or twice or more, the switching level of the switching diode
21
as indicated by the crossing part of the solid line and the chain line in FIG.
4
. During the period in which the logical low level is exceeding the switching level, the switching diode
21
turns ON and thereby the carrier signal is transmitted through the switching diode
21
.
As explained above, the ASK modulator of the related art has a problem that it is impossible to derive an errorless ASK modulated signal at the ASK modulated signal output end
28
because the carrier signal is transmitted in the temporary ON condition of the switching diode
21
caused by the ringing phenomenon during the period where transmission of the carrier signal should be rejected.
SUMMARY OF THE INVENTION
The present invention has been proposed to solve the problem explained above and it is therefore an object of the present invention to provide an ASK modulator which can extract errorless ASK modulated signal even if the ringing phenomenon is generated when the digital signal changes from a logical high level to a logical low level.
In view of attaining the object explained above, there is provided, in the ASK modulator of the present invention, means for substantially raising the switching level of a switching diode by dividing the ASK modulator of the digital signal with a series connected first resistor and a shunt connected second resistor and supplying the divided digital signal to a switching diode.
According to this means, since the divided digital signal is supplied to the switching diode to substantially raise the switching level of the switching diode, if the ringing phenomenon in which the logical low level changes in the high and low direction immediately after the digital signal changes to the logical low level from the high level, the high level part generated by the ringing phenomenon does not exceed the switching level of the switching diode and during the period that the digital signal becomes the logical low level, the switching diode always becomes OFF not to transmit the carrier signal. Thereby, an errorless ASK modulated signal can be obtained from the ASK modulated signal output end.
In the principal embodiment of the present invention, the ASK modulator supplies the carrier signal and digital signal divided by resistor to a switching element to generate the ASK modulated signal.
In a preferred embodiment of the
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Kinkead Arnold
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