Amplifiers – Signal feedback – Variable impedance in feedback path varied by separate...
Reexamination Certificate
1999-11-03
2001-06-12
Pascal, Robert (Department: 2817)
Amplifiers
Signal feedback
Variable impedance in feedback path varied by separate...
C330S308000, C250S2140AG
Reexamination Certificate
active
06246282
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a first stage amplifier circuit, and in particular, to a first stage amplifier circuit having a wide dynamic range.
DESCRIPTION OF THE PRIOR ART
Due to rapid progress of information processing technology and optical data transmission technology of these days, both the capacity and the distance of optical data transmission are growing increasingly, and thereby optical data transmission techniques for implementing a very high data transmission bit rate are now being required. Various optical data transmission techniques have been proposed for realizing high capacity optical data transmission, and along with introduction of such techniques, high reception sensitivity is also being required of optical data reception devices. In addition to the high reception sensitivity, such optical data reception devices also requires a wide dynamic range so as to be applicable in a wide variety of circumstances, since there are cases where the optical data reception device has to receive a high level optical signal which has been transferred via a short line for intra-station data transmission, a high level optical signal transmitted by an optical amplifier for a loopback test of the station, etc. Such a wide dynamic range is especially required of the first stage amplifier circuit of the optical data reception device.
FIG. 1
is a circuit diagram showing a multistage preliminary amplifier including a conventional first stage amplifier circuit having a wide dynamic range. The multistage preliminary amplifier of
FIG. 1
has three stages of amplifier circuits, including a first stage amplifier circuit
10
-
1
, a second stage amplifier circuit
10
-
2
, and a third stage amplifier circuit
10
-
3
.
The output signal of the first stage amplifier circuit
10
-
1
is supplied to the input terminal of the second stage amplifier circuit
10
-
2
, and the output signal of the second stage amplifier circuit
10
-
2
is supplied to the input terminal of the third stage amplifier circuit
10
-
3
. The output signal of the third stage amplifier circuit
10
-
3
is outputted from the output terminal
11
of the multistage preliminary amplifier to outside. The output signal of the third stage amplifier circuit
10
-
3
is also fed back to the input terminal of the first stage amplifier circuit
10
-
1
via a feedback resistor
12
. To the input terminal of the first stage amplifier circuit
10
-
1
, the anode of a photodiode (PD)
13
is connected. A power source voltage Vcc is applied to the cathode of the PD
13
, and thereby the PD
13
is reversely biased. Due to the reverse bias connection, when a photo (optical) signal P incidents upon the PD
13
, photocurrent I occurs depending on the intensity of the photo signal P, and the photocurrent I is supplied to the input terminal of the first stage amplifier circuit
10
-
1
. The output terminal and the input terminal of the first stage amplifier circuit
10
-
1
is connected via a variable impedance element
14
.
The output terminal of the first stage amplifier circuit
10
-
1
is also connected to the input terminal of a level shift amplifier
15
. The output terminal of the level shift amplifier
15
is connected to a peak detection section
16
and a signal synthesis section
17
. The peak detection section
16
detects and holds the peak level of the amplified output of the level shift amplifier
15
, and informs the signal synthesis section
17
of the peak level. The signal synthesis section
17
synthesizes a signal using the amplified output of the level shift amplifier
15
and the peak level informed by the peak detection section
16
, and supplies the synthesized signal to the variable impedance element
14
.
In the following, the operation of the conventional multistage preliminary amplifier of
FIG. 1
will be described briefly. When a photo signal P (in the shape of pulses, for example) is supplied to the PD
13
, photocurrent I (in the form of pulses) of an amplitude corresponding to the intensity of the photo signal P occurs, and the photocurrent I is supplied to the first stage amplifier circuit
10
-
1
. The pulse signal from the PD
13
is successively amplified by the first stage amplifier circuit
10
-
5
1
, the second stage amplifier circuit
10
-
2
, and the third stage amplifier circuit
10
-
3
. In the amplification, the gain of the first stage amplifier circuit
10
-
1
near the level “0” of the 1/0 pulse input signal is prevented from becoming high, in order to secure the difference between signals “0” and “1” amplified and outputted by the first stage amplifier circuit
10
-
1
even if the first stage amplifier circuit
10
-
1
is saturated by a pulse signal of a very high level. The reduction of the 0 level gain of the first stage amplifier circuit
10
-
1
is executed as follows. The output of the variable impedance element
14
and the output of the first stage amplifier circuit
10
-
1
are added together, and the added signal is slightly amplified by the level shift amplifier
15
. The peak level of the slightly amplified signal is detected and held by the peak detection section
16
. The signal synthesis section
17
synthesizes a signal using the slightly amplified signal from the level shift amplifier
15
and the peak level informed by the peak detection section
16
, and supplies the synthesized signal to the variable impedance element
14
. The resistance of the variable impedance element
14
(which changes depending on the synthesized signal supplied from the signal synthesis section
17
) becomes almost 0 with respect to 0 level signals supplied thereto, thereby the gain of the first stage amplifier circuit
10
-
1
near the level “0” of the 1/0 pulse signal is reduced, and thereby the difference between signals “0” and “1” amplified and outputted by the first stage amplifier circuit
10
-
1
is secured even if the first stage amplifier circuit
10
-
1
is saturated by a high level pulse signal.
By such an operation for widening the dynamic range of the first stage amplifier circuit
10
-
1
, change of the pulse widths of the pulse signal which is amplified by the multistage preliminary amplifier and outputted from the output terminal
11
is avoided, that is, duty distortion of the pulse signal in the amplification is prevented. Such techniques for a first stage amplifier circuit of a multistage preliminary amplifier have been disclosed in Japanese Patent Application Laid-Open No.HEI7-38342: “Preliminary Amplifier”.
High speed optical fiber data transmission systems have widely been in practical use today, and the PON (Passive Optical Network) system has been proposed as an optical fiber network for constructing the FTTH (Fiber To The Home) system as a next-generation communication network. In the PON system, communication of burst signals is executed, and thus a terminal has to receive a variety of burst signals which are supplied from terminals of various distances in a star-type network connected by optical couplers. Therefore, an optical data reception device in the PON system is required to receive such burst signals correctly regardless of whether the signal level is high or low, that is, a wide dynamic range is required of the optical data reception device. Further, the optical data reception device is required high speed response capable of receiving and transmitting the burst signals correctly. In the reception and amplification of the burst signals, change of duty rate of the received burst signal (i.e. duty distortion) has to be eliminated in order to realize high speed extraction and low extraction error in a clock recovery device (a PLL (Phase Locked Loop), etc.) which is connected after the optical data reception device.
However, the conventional first stage amplifier circuit having a wide dynamic range which has been shown in
FIG. 1
is implemented by feedback AGC (Automatic Gain Control) which is composed of an analog circuit, therefore, high speed response of the circuit is limited by the time constant of the analog circuit, and thus
Oono Hiroshi
Yokomizo Masaaki
Choe Henry
McGinn & Gibb PLLC
NEC Corporation
Pascal Robert
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