Amplifiers – Sum and difference amplifiers
Reexamination Certificate
2003-03-25
2004-11-02
Nguyen, Khanh Van (Department: 2817)
Amplifiers
Sum and difference amplifiers
C330S009000
Reexamination Certificate
active
06812787
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a voltage amplifier for amplifying input signals having a variety of signal amplitudes, such as a signal obtained through current/voltage conversion of an output current from a photodiode that receives an optical signal from an optical fiber, to a constant amplitude in optical communications systems such as a PDS Passive Double Star) optical subscriber system.
In recent years, vigorous studies have been carried out on optical subscriber systems in order to realize future FTTH (Fiber To The Home) services. However, the introduction of an optical fiber, which has extremely large transmission capacity, to households presents the problem that it is less cost effective than conventional metallic cables. Under this circumstance, the PDS optical subscriber system is considered promising from the viewpoint of cost effectiveness, since it has enabled a two-way communications service to a plurality of subscribers by splitting a single optical fiber supplied by the station side.
In such an optical communications system, as the distances between individual households and the station differ from one another, so do the optical fiber transmission distances. The attenuation of light also varies between them, and signals obtained through photoelectric conversion at an optical link section of a light receiving device, are turned into voltage signals having a variety of amplitudes, including signals having a very small amplitude and signals having a large amplitude. In order to extract clocks and data from these voltage signals, it is necessary to amplify the signals to voltage signals having a constant amplitude of a level at which digital processing is possible.
However, if the gain is set high for input signals having a small amplitude when amplifying the signals with a commonly used amplifier, an offset causes saturation of the output, or the output signal saturates and greatly distorts the waveform when signals having a large amplitude are input, thereby making it impossible to extract clocks and data.
In view of this, there has been proposed an amplifying circuit as disclosed in Japanese Laid Open Patent Publication No. 6-310967. In the configuration of this amplifying circuit, a peak value and a bottom value of an input signal are each detected and held, and an intermediate voltage value of these values and the input signal are input to an amplitude limiting amplifier.
The amplifying circuit proposed by the above-mentioned publication, however, requires two peak detecting circuits, namely, a peak value detecting-and-holding circuit and a bottom value detecting-and-holding circuit, resulting in increased power consumption. Furthermore, it also requires a circuit for dividing the output voltages of the above-mentioned circuits. In order to increase the response speed of this voltage dividing circuit, it is necessary to decrease the value of the resistance used for the voltage division, promoting the increase of power consumption further.
Additionally, a time period in which the intermediate voltage of the peak value and the bottom value is generated and stabilized is the sum of a time period in which the output of each of the peak value detecting-and-holding circuit and the bottom value detecting-and-holding circuit is stabilized and a time period in which the output of the voltage dividing circuit is stabilized, so that there is the problem of a significant time delay.
SUMMARY OF THE INVENTION
Therefore, with the foregoing in mind, it is an object of the present invention to provide a reference voltage generating circuit with low power consumption that is excellent in the high-speed response performance, and a voltage amplifier that uses the same to amplify input signals having a variety of signal amplitudes to a constant amplitude.
In order to solve the above-mentioned object, according to the present invention, a reference voltage between the maximum peak value and the minimum peak value of an input signal is automatically generated at the time when these peak values are detected.
More specifically, the present invention provides a reference voltage generating circuit wherein a signal is input, a maximum peak value or minimum peak value of the input signal in a first period is detected and held as a first peak value, a minimum peak value or maximum peak value of the input signal in a second period different from the first period is detected and held as a second peak value, and a voltage between the first peak value and the second peak value is output as a reference voltage.
According to the present invention, the reference voltage generating circuit comprises: a first capacitor; and a capacitor string comprising a cascade connection of a second and a third capacitor, wherein: the first peak value is held in the first capacitor, and a voltage difference between the first peak value and the second peak value is held in the capacitor string; and a voltage held in the second capacitor is added to a voltage held in the first capacitor, and the voltage thus obtained is output as a reference voltage.
According to the present invention, in the reference voltage generating circuit, a capacitance value of the second capacitor and a capacitance value of the third capacitor are equal.
According to the present invention, in the reference voltage generating circuit, the first capacitor and the capacitor string are cascade-connected.
According to the present invention, in the reference voltage generating circuit, a capacitance value of the first capacitor is sufficiently larger than the capacitance values of the second and the third capacitors.
The present invention also provides a reference voltage generating circuit comprising: a first capacitor; a capacitor string comprising a cascade connection of a second and a third capacitor; a voltage/current converting circuit for outputting a current corresponding to a voltage difference between two input voltages input to two input terminals; a unidirectionally-conductive element for passing a current only in one direction; a buffer circuit; and first and second reset circuits, wherein: an output terminal of the voltage/current converting circuit is connected to one end of the unidirectionally-conductive element; the other end of the unidirectionally-conductive element is connected to one end of the capacitor string and to an input terminal of the buffer circuit; the other end of the capacitor string is connected to one end of the first capacitor; a predetermined voltage is applied to the other end of the first capacitor; an output terminal of the buffer circuit is connected to one input terminal of the voltage/current converting circuit, and a signal is input to the other input terminal of the voltage/current converting circuit; the first reset circuit discharges an electric charge of the first capacitor; and the second reset circuit discharges electric charges of the second and third capacitors constituting the capacitor string.
The present invention provides a reference voltage generating circuit comprising: a voltage generating circuit for generating a predetermined voltage; and a capacitor string comprising a cascade connection of two capacitors, wherein: one end of the capacitor string is connected to an output terminal of the voltage generating circuit, and a peak value of an input signal is detected and held on the other end of the capacitor string; and a voltage at a node connecting the two capacitors constituting the capacitor string is output as a reference voltage.
According to the present invention, in the reference voltage generating circuit, capacitance values of the two capacitors constituting the capacitor string are equal to each other.
The present invention also provides a reference voltage generating circuit comprising: a voltage generating circuit for generating a predetermined voltage; a capacitor string comprising a cascade connection of two capacitors; a voltage/current converting circuit for outputting a current corresponding to a voltage difference between two input volta
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