Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Amplitude control
Reexamination Certificate
1999-07-14
2001-05-15
Wells, Kenneth B. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Amplitude control
C327S362000, C327S513000
Reexamination Certificate
active
06232817
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method of stabilising the working point of a predistorter diode of a predistorter for an optical modulator as protection from temperature fluctuations, whereby the predistorter diode is supplied with temperature-dependent voltage in order to adjust the working point.
In order to adjust the working point of a diode in a network which influences the signal, voltage impression is known on the one hand, and current impression on the other. U.S. Pat. No. 5,161,044, FIG. 15, shoes a diode network to linearise the output signal of an external optical modulator through which the light leaving a light source is modulated. The diodes here are connected with voltage sources. As these are semiconductor diodes, their current/voltage characteristic is dependent on temperature. Accordingly, the working point of the diode changes under temperature changes without any special measures, because the voltage supplied to the diode is constant. Also known is guidance of the voltage of predistorter diodes by means of a computer according to a temperature table, whereby a temperature sensor and an analog/digital converter and a digital/analog converter are required. However, this creates a relatively large workload.
In addition, an arrangement with current impression is known from U.S. Pat. No. 5,210,633, FIG. 2. In this arrangement, the DC voltage at the diode changes depending on the level fluctuations of the signal passed through the diode, which can be a high-frequency signal. In this known arrangement, when the diode network consists of a predistorter for linearising the output signal of an optical modulator, it is possible for the working point to be optimally adjusted just for one single value of the amplitude of the high frequency signal. In this known arrangement, it is necessary to guide the current source according to the amplitude for optimum linearisation of the characteristic curve.
SUMMARY OF THE INVENTION
The invention is based on the task of reducing by simple means the temperature dependence of a predistorter diode fed with voltage in order to adjust the working point. This task is solved by the present invention by the fact that a reference diode is thermally coupled with the predistorter diode, that the reference diode is supplied with a constant current, whereby it is not supplied with a signal distorted by the predistorter, and that the predistorter diode is fed with a voltage which is proportional to the voltage at the reference diode.
The invention also includes an apparatus for stabilising the working point of a predistorter diode of a predistorter, and a predistorter of an external optical modulator.
One advantage of the invention is the fact that good temperature stability is achieved in a simple way. The current supply to the reference diode means that its current is not dependent on temperature. Ageing of the predistorter diode is not a problem because the reference diode also ages. It may be sufficient to use as reference diode a diode whose properties relating to change of the working point under temperature change are similar to but not fully identical with the predistorter diode. But it is particularly beneficial and easy to take the same type of diode for the reference diode as for the predistorter diode. Seeing that no high frequency is supplied to the reference diode, the working point of the reference diode and thus the voltage here changes only depending on the temperature.
One further advantage is that the predistorter diode is decoupled from the current supplied to the reference diode. An amplifier, or preferably an operation amplifier, can be used for this purpose. Another advantage is that the voltage loss at the reference diode is fed to the predistorter diode by means of an operation amplifier. A control unit is given particular preference here.
REFERENCES:
patent: 3914624 (1975-10-01), Jackson
patent: 5161044 (1992-11-01), Nazarathy et al.
patent: 5162678 (1992-11-01), Yamasaki
patent: 5172068 (1992-12-01), Childs
patent: 5210633 (1993-05-01), Trisno
patent: 5939920 (1999-08-01), Hiraizumi
patent: 6037823 (2000-03-01), Arai et al.
patent: WO 97/35390 (1997-09-01), None
Berger Werner
Braun Klaus
Alcatel
Dinh Paul
Sughrue Mion Zinn Macpeak & Seas, PLLC
Wells Kenneth B.
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