Amplifiers – With semiconductor amplifying device – Including atomic particle or radiant energy impinging on a...
Reexamination Certificate
2002-06-12
2003-07-01
Pascal, Robert (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including atomic particle or radiant energy impinging on a...
C250S2140AG
Reexamination Certificate
active
06587004
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a signal amplifier and an optical signal receiver using the same, and more particularly, a signal amplifier suitable for amplification of a burst signal and a burst optical signal receiver using the same.
BACKGROUND OF THE INVENTION
In recent years, there has been increased expectation of a high-speed burst optical transmission system such as a PON (passive optical system) for use in an optical subscriber system.
In
FIG. 1
, a conceptual diagram of the PON system is shown. A plurality of subscribers #
1
-#n are connected to a coupler
200
through optical transmission lines
200
-
1
-
200
-n. Further, coupler
200
and an switching office
201
are interconnected through an optical backbone line
202
.
A cell-formed optical signal in a burst form is output from each of the plurality of subscribers #
1
-#n. The optical signals
203
-
205
are forwarded to switching office
201
through coupler
200
and optical backbone line
202
.
Here, as shown in
FIG. 1
, the distance between coupler
200
and each of the plurality of subscribers #
1
-#n is different, resulting in different levels of cell-formed optical signals being output from coupler
200
. This necessitates an optical signal receiver on the switching office to have a wide input dynamic range so as to amplify these signals in common.
In
FIG. 2
, there is shown an exemplary configuration of the optical signal receiver for receiving the optical burst signals under the aforementioned condition, which was formerly proposed by the inventor of the present invention. In
FIG. 2
, an optical signal is received in a photodiode (PD)
100
, to convert into an electric current signal. The signal is then input to a pre-amplifier
101
.
Pre-amplifier
101
converts this electric current signal into a voltage signal. A trans-impedance amplifier
103
constituting pre-amplifier
101
includes an amplifier
103
A having a diode
103
C connected in parallel with a feedback resistor
103
B, so as to produce a wider dynamic range.
When an excessive input signal is received, diode
103
C is turned on to reduce the feedback resistance so as to prevent the amplifier from saturation. Thus, desirable output waveform having a wide input dynamic range can be obtained from a buffer amplifier
104
incorporating a signal polarity inverting function.
Signal amplifier
102
is constituted by a master-slave automatic threshold control (ATC) circuit
106
and a limiter amplifier
108
. Signal amplifier
102
amplifies a weak signal being output from buffer amplifier
104
provided in pre-amplifier
101
to obtain logic signals of sufficient level.
Master-slave ATC circuit
106
includes a master peak detector
106
B for detecting the maximum input signal value and a slave bottom detector
106
A for detecting a relatively minimum value from the peak detection level. These outputs are resistively divided by a serially connected resistive voltage divider
106
C. Thus an intermediate value is obtained as a DC voltage level for setting a threshold level against a limiter amplifier
108
.
Now, in each subscriber #
1
-#n, optical signal is emitted by driving a laser diode. Here, bias current is made to flow from a few bits before the cell-formed optical signal. This reduces light emission delay and improves output waveform.
In
FIG. 3
, there is shown a diagram of input current amplitude versus output voltage amplitude in pre-amplifier
101
in the optical signal receiver shown in FIG.
2
. An extinction ratio on transmitter in driving the laser is, for example, on the order of 10 dB or less. Input current amplitude I includes DC level II, as a bias current, corresponding to the extinction ratio mentioned above.
Meanwhile, as shown in the figure, the characteristic of input current amplitude versus output voltage amplitude in pre-amplifier
101
becomes nonlinear because of diode
103
C. This produces a large amount of ascent on the ‘0’ level in the output III of pre-amplifier
101
.
As a result, a problem arises that the amplitude level to be detected by bottom detector
106
A becomes higher than the transient minimum value. To cope with this problem, master-slave ATC circuit
106
is applied in signal amplifier
102
, as shown in FIG.
2
. This enables to detect the signal amplitude level certainly, because the use of slave bottom detector
106
A enables to detect the minimum value after the peak level is determined.
However, the signal amplifier shown in
FIG. 2
, which has formerly been proposed by the inventors of the present invention, is used for one-way signal transmission. There is a problem that the signal is possibly deteriorated caused by external noise, etc.
Namely, when an external noise enters in the transmission line between pre-amplifier
101
and signal amplifier
102
, there arises a drift in the input signal. In such a case, the output signal of limiter amplifier
108
is drifted because the threshold value produced from voltage divider
106
C responds slowly and, as a result, little variation is produced. This produces difficulty in normal transmission.
FIG. 4
shows signal waveform responses {circle around (
1
)} to {circle around (
6
)} at the corresponding positions of signal amplifier
102
shown in FIG.
2
. In
FIG. 4A
, the peak value and the bottom value of the input signal waveform response {circle around (
1
)} are detected by peak detector
106
B and bottom detector
106
A, respectively.
The example shown in
FIG. 4A
illustrates a case that an external noise enters at the part of input signal waveform response {circle around (
1
)} shown by the circle with the broken line. In
FIG. 4B
, there is shown an example that the intermediate value between the peak value and the bottom value is set as a threshold value {circle around (
4
)} by voltage divider
106
C.
Further,
FIG. 4
illustrates that a normal phase output {circle around (
5
)} and an inverse phase output {circle around (
6
)} are obtained as the output signals. These outputs are derived from the input signal waveform response {circle around (
1
)} being referenced from the threshold value {circle around (
4
)}. It is to be understood that noise component included in the output remains unchanged.
As shown in
FIG. 4C
, according to the configuration of the optical receiver shown in
FIG. 2
, there is a problem that waveform deterioration is produced by external noise, etc., because of single signal transmission.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a signal amplifier configuration and an optical signal receiver using the same. This can solve the problem of waveform deterioration produced by external noise, etc. in a signal amplifier of the formerly invented optical signal receiver shown in FIG.
2
.
According to the present invention, an optical signal receiver to solve the aforementioned problem includes; a first master-slave level detector for detecting a direct voltage level of a normal phase signal; and a second master-slave level detector for detecting a direct voltage level of an inverse phase signal. Differential signal transmission is realized by adding respective signals to the signal components alternately. Thus, according to the present invention, differential transmission becomes possible using two master-slave level detectors constituted by mutually symmetric configuration. It becomes possible to obtain a signal amplifier which can cope with various transient responses produced at the top of a burst cell, and to protect against the disturbance produced by external noise.
As one aspect of the present invention, there is provided a signal amplifier including; a first level detector for detecting a direct voltage level of a normal phase signal; a first adder for adding an inverse phase signal to the detection output of the first level detector; a second level detector for detecting a direct voltage level of the inverse phase signal; a second adder for adding the normal phase signal to the detection output of the second
Fujitsu Limited
Katten Muchin Zavis & Rosenman
Nguyen Khanh Van
LandOfFree
Signal amplifier and optical signal receiver using the same does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Signal amplifier and optical signal receiver using the same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Signal amplifier and optical signal receiver using the same will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3037851