Pulse or digital communications – Equalizers
Reexamination Certificate
1998-10-30
2002-01-01
Pham, Chi (Department: 2631)
Pulse or digital communications
Equalizers
C327S060000
Reexamination Certificate
active
06335948
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to an amplitude detector and an equalizer.
When a video signal of R (Red), G (Green), and B (Blue) for example is transmitted through a copper monitor cable, the amplitude of the signal is detected by a destination receiver and, based on the detection result, the signal of which amplitude has been attenuated by transmission is amplified to restore the original signal.
FIG. 7
shows a constitution of a related-art amplitude detector
1
arranged in a receiver. As shown, the amplitude detector
1
has a capacitor
2
, a full-wave rectifier
3
, and a peak-hold circuit
4
. In the amplitude detector
1
, the DC component of a video signal S
0
transmitted over a monitor cable is removed by the capacitor
2
and the AC component S
2
of the video signal S
0
shown in
FIG. 8
is outputted to the full-wave rectifier
3
. In the full-wave rectifier
3
, the AC component S
2
is full-wave rectified into a signal S
3
shown in FIG.
8
. In the peak-hold circuit
4
, the peak voltage of the signal S
3
is detected and an amplitude detect signal S
1
for holding this peak voltage is outputted.
FIG. 9
shows a constitution of another related-art amplitude detector
11
arranged in a receiver.
As shown, the amplitude detector
11
has a capacitor
2
, a positive peak-hold circuit
13
, a negative peak-hold circuit
14
, and an operational amplifier
15
. In the amplitude detector
11
, the DC component of a video signal S
0
transmitted over a monitor cable is removed by the capacitor
2
and an AC component S
2
of the video signal S
0
shown in
FIG. 10
is outputted to the positive peak-hold circuit
13
and the negative peak-hold circuit
14
. In the positive peak-hold circuit
13
, the positive peak voltage of the AC component S
2
is detected and a signal S
13
for holding the detected peak voltage is outputted. In the negative peak-hold circuit
14
, the negative peak voltage of the AC component S
2
is detected and a signal S
14
for holding the detected peak voltage is outputted as shown in FIG.
10
. In the operational amplifier
15
, a differential voltage between the signal S
14
and the signal S
13
is detected and the detected differential voltage is outputted as an amplitude detect signal S
11
. According to the amplitude detector
11
, the peak-to-peak amplitude of the AC component S
2
of the video signal S
0
can be correctly detected theoretically.
However, in the amplitude detector
1
shown in FIG.
7
, if the duty ratio of the video signal S
0
is deviated from 0.5, the amplitude detect signal S
1
shown in
FIG. 8
does not become a half of the peak-to-peak amplitude of the AC component
2
, causing an error in a measured value. Consequently, the attenuated amplitude of the video signal S
0
cannot be properly amplified for restoring the original signal.
Theoretically, the amplitude detector
11
shown in
FIG. 9
can correctly detect the peak-to-peak amplitude of the AC component S
2
of the video signal S
0
. Actually, however, the characteristic of the positive peak-hold circuit
13
and the characteristic of the negative peak-hold circuit
14
are not exactly in symmetry, so that an error occurs also in the amplitude detect signal S
11
.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an amplitude detector capable of properly detecting an amplitude of a video signal for example.
In carrying out the invention and according to one aspect thereof, there is provided an amplitude detector comprising: a first peak holding means for generating a first peak voltage signal for holding a peak voltage of a detected signal; a differential signal generating means for generating a differential signal between the first peak voltage signal and the detected signal; and a second peak holding means for generating an amplitude detect signal holding a peak voltage of the differential signal.
In carrying out the invention and according to another aspect thereof, there is an amplitude detector comprising: a first peak holding means for generating a first peak voltage signal for holding a peak voltage of a detected signal; a first differential signal generating means for generating a first differential signal between the first peak voltage signal and the detected signal; a second peak holding means for generating a first amplitude detect signal holding a peak voltage of the first differential signal; a third peak holding means for generating a third peak voltage signal for holding a peak voltage of a reference signal; a second differential signal generating means for generating a second differential signal between the third peak voltage signal and the reference signal; a fourth peak holding means for generating a second amplitude detect signal holding a peak voltage of the second differential signal; and a third differential signal generating means for generating a third amplitude detect signal corresponding to a difference between the first amplitude detect signal and the second amplitude detect signal.
In the amplitude detector according to the invention, if the duty ratio of the input signal varies to vary an DC offset, the waveform of the first peak voltage signal follows the peak value of the input signal. Therefore, in the differential signal generating means, obtaining the difference between the first peak voltage signal and the input signal can obtain the differential signal indicative of the potential of the input signal relative to the first peak voltage signal. In the differential signal, the DC offset is canceled. Therefore, the amplitude detect signal having the peak-hold waveform of the differential signal correctly reflects the amplitude of the input signal relative to the output potential of the amplitude detect signal when the amplitude of the input signal is zero.
In carrying out the invention and according to still another aspect thereof, there is provided an equalizer comprising: a filter means for extracting a high-frequency component from an input signal to provide a first signal; a first amplifying means for amplifying, based on an amplification factor control signal, the first signal to generate a second signal; a second amplifying means for amplifying the input signal to generate a third signal; a superimposing means for superimposing the second signal and the third signal on each other to generate a fourth signal; and an amplitude detecting means for detecting an amplitude of the fourth signal to generate, based on the detected amplitude, the amplification factor control signal; the amplitude detecting means having a first peak holding means for generating a first peak voltage signal for holding a peak voltage of the fourth signal, a first differential signal generating means for generating a first differential signal between the first peak voltage signal and the fourth signal, a second peak holding means for generating a first amplitude detect signal holding a peak voltage of the first differential signal, a third peak holding means for generating a third peak voltage signal for holding a peak voltage of a reference signal, a second differential signal generating means for generating a second differential signal between the third peak voltage signal and the reference signal, a fourth peak holding means for generating a second amplitude detect signal holding a peak voltage of the second differential signal, and a third differential signal generating means for generating the amplification factor control signal corresponding to a difference between the first amplitude detect signal and the second amplitude detect signal.
REFERENCES:
patent: 5589778 (1996-12-01), Ono et al.
patent: 5694064 (1997-12-01), Watanabe et al.
patent: 5952883 (1999-09-01), Masuta
patent: 5955918 (1999-09-01), Uno
Kananen Ronald P.
Rader & Fishman & Grauer, PLLC
Tran Khai
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