Amplifiers – With semiconductor amplifying device – Including gain control means
Reexamination Certificate
1999-07-23
2001-09-18
Mottola, Steven J. (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including gain control means
C330S136000
Reexamination Certificate
active
06292058
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a signal amplifying circuit, and in particular to a signal amplifying circuit connected to a transfer circuit having a non-linear transfer characteristic and a transient characteristic.
Generally, signal transfer circuits or transmission lines may have a non-linear transfer characteristic. This non-linear transfer characteristic is positively used in an optical receiving circuit of an optical subscriber system, and is indispensable for extending the dynamic range of an amplifying circuit. In addition, a preamplifier for converting an optical signal into an electric signal has a “0” level rise peculiar to an optical signal transmission and a tailed response characteristic as a transient phenomenon. The signal amplifying circuit connected to the preamplifier is required to deal with such a response characteristic.
2. Description of the Related Art
FIG. 42
shows an example of a prior art signal amplifying circuit (
1
) having a preamplifier
20
with a non-linear transfer characteristic at the former stage. In the preamplifier
20
, after having been converted into an input current signal I by a photo diode
10
, a burst optical input signal
100
of an optical subscriber system is inputted to an amplifier
21
having a feedback resistor
22
and a diode
23
with a non-linear characteristic.
If the direction of an arrow indicating the current signal I in
FIG. 42
is assumed to be positive, a signal
101
which is the output signal of the amplifier
21
has a negative logic. Also, the optical input signal
100
from subscribers comprises burst signals whose amplitudes are largely different from each other. The preamplifier
20
and a signal amplifying circuit
30
are required to instantaneously respond at the leads of the burst signals (in a wide range).
The signal amplifying circuit
30
is composed of a threshold generation circuit
33
for receiving the input signal
101
from the preamplifier
20
and outputting a threshold signal
106
, and a limiter amplifier
31
which is a differential input/output amplifying circuit for inputting the input signal
101
and the threshold signal
106
and outputting output signals
102
and
103
.
The threshold generation circuit
33
is composed of a peak detection circuit
34
and a bottom detection circuit
35
for commonly inputting the input signal
101
, and a voltage divider
36
for inputting a peak detection signal
104
and a bottom detection signal
105
which are the outputs of the detection circuits
34
and
35
and outputting the threshold signal
106
having a partial voltage between a peak level and a bottom level.
FIGS. 43A and 43B
show the amplifying characteristics of the preamplifier
20
and the signal amplifying circuit
30
. The circuit operation of
FIG. 42
will now be described referring to
FIGS. 43A and 43B
.
FIG. 43A
shows the transfer characteristic A of the preamplifier
20
, that is the relationship between the input current signal I and the output amplitude (=the amplitude of the input signal
101
), and shows a threshold level L
1
set by the threshold generation circuit
33
of the signal amplifying circuit
30
, that is the relationship between the input current I and the threshold signal
106
.
The transfer characteristic A reveals a linear characteristic determined by a feedback resistor
22
in the range from the input current
0
to I
1
, and reveals a compressed curved line with a non-linear characteristic of the diode
23
further added in the range over the input current I
1
.
This is because the preamplifier
20
prevents the output signal resistance including the resistance of the diode
23
to enhance the negative-feedback effect in order to extend the dynamic range of the optical input signal
100
when the preamplifier
20
receives the optical input signal
100
having an excessive amplitude.
The threshold level L
1
indicates the level of the threshold signal
106
which corresponds to a partial voltage between the peak detection signal
104
and the bottom detection signal
105
which are respectively detected by the peak detection circuit
34
and the bottom detection circuit
35
with respect to the input signal
101
from the preamplifier
20
, the partial voltage being provided by resistors
41
and
42
having the same resistance as an example. Accordingly, the threshold level L
1
is a half level of the amplitude of the input signal
101
shown by the transfer characteristic A.
FIG. 43B
shows a pulse width B of the input signal
101
outputted by the preamplifier
20
and a pulse width C of the output signals
102
and
103
outputted by the signal amplifying circuit
30
with respectively being made correspond to the amplitude of the input signal
101
, assuming that the pulse width of the optical input signal
100
has 100% (a single time slot).
It is to be noted that the amplitude of the input signal
101
indicates the difference between the peak level and the bottom level of the signal
101
, and the pulse width of the input signal
101
indicates a signal width at an intermediate level between the peak level and the bottom level of each signal according to the above-mentioned example.
The pulse width B is the same as that of the optical signal
100
when the amplitude of the input signal
101
is small, while the pulse width B greatly varies from a vicinity of a control initiation level V
1
of the amplitude due to the non-linear transfer characteristic of the preamplifier
20
. Since the signal amplifying circuit
30
which inputs a signal having the pulse width B performs a linear operation, it generates the output signals
102
and
103
which have the pulse width C substantially the same as the pulse width B.
FIGS. 44A and 44B
show an example of an operation waveform in the operation of the signal amplifying circuit
30
.
FIG. 44A
shows an example in which the amplitude of the optical input signal
100
is small, so that the preamplifier
20
linearly amplifies the optical input signal
100
. Accordingly, the pulse width of the input signal
101
is the same as that of the optical input signal
100
.
The signal amplifying circuit
30
outputs the output signals
102
and
103
based on the threshold signal
106
which has an intermediate level between the peak detection signal
104
and the bottom detection signal
105
of the input signal
101
. Accordingly, the pulse width of the output signals
102
and
103
is substantially the same as that of the optical input signal
100
.
FIG. 44B
shows an example in which the amplitude of the optical input signal
100
is large, so that the preamplifier
20
compresses and amplifies the side of logic “1” of the optical input signal
100
to output the signal
101
deteriorated in the direction of widening the pulse width as shown by a dotted line. Accordingly, the pulse width of the output signals
102
and
103
the signal amplifying circuit
30
outputs based on the threshold signal
106
which has an intermediate level between the peak detection signal
104
and the bottom detection signal
105
is larger than the pulse width of the optical input signal
100
.
Also, there is a problem on the level of the threshold signal
106
generated by the threshold generation circuit
33
that the pulse width is further deteriorated. Therefore, a necessary eye pattern (aperture) can not be obtained especially when the input signal is small because the level of the threshold signal
106
deviates from the central position of the signal due to the offset or the like.
In order to solve this problem, measures such as correcting the pulse width by using an average value of the input signal have been taken when the input signal is a continuous transmission signal. However, since an average value circuit such as an LPF is slow to respond, it is impossible to apply the LPF for the transmission of the burst signal which requires an instantaneous response at the lead of the input signal.
In such a prior art signal amplifying circuit, there has be
Ide Satoshi
Shibata Kohei
Fujitsu Limited
Helfgott & Karas P.C.
Mottola Steven J.
LandOfFree
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