Dispersion compensation circuitry and system for analog video transmission with direct modulated laser
View Patent ↗An improved precompensation circuit includes a greatly improved differentiator in the dispersion precompensation path, a preprocessor in the dispersion precompensation path for reducing f2−f1 type Composite Second Order (CSO) distortion, and a broadband phase shifter for compensating undesired vector interaction between the laser predistortion and dispersion compensation.
1. A phase shifter comprising:
an input port for receiving an input electronic signal;
a splitter having an input connected to the input port and having first and second electronic outputs, the splitter delivering at least three times the signal power level to the first output as it delivers to the second output;
a combiner having first and second inputs and further having an output for carrying a phase shifted version of the input signal;
a first signal path connecting the first output of the splitter to the first input of the combiner; and
a second signal path connecting the second output of the splitter to the second input of the combiner, the second signal path including an electronic variable attenuator and an electronic all-pass network having an input and a first output, the input and first output of the all-pass network being connected in series combination with the variable attenuator, wherein the all-pass network provides on its first output a version of the signal on its input which is shifted in phase by a phase angle φ+90°, where 0<φ<90°.
2. A phase shifter according to claim 1 , wherein the first signal path includes a fixed time delay element.
3. A phase shifter according to claim 1 , wherein the all-pass network further has a second output on which the all-pass network provides a version of the signal on its input which is shifted in phase by phase angle φ,
and wherein the second output of the all-pass network is terminated.
4. A phase shifter according to claim 1 , wherein the variable attenuator is an impedance matched network.
5. A phase shifter according to claim 1 , further comprising a selective phase inverter connected serially in the second signal path.
6. A phase shifter according to claim 5 , wherein the selective phase inverter comprises:
an input node and an output node connected in series combination with the variable attenuator and the all-pass network;
an input switch connecting the input node of the selective phase inverter to selectively a first or a second throw terminal;
an output switch connecting selectively a first or a second throw terminal to the output node of the selective phase inverter;
a 180° phase shifter connected between the first throw terminal of the input switch and the first throw terminal of the output switch; and
a 0° phase shifter connected between the second throw terminal of the input switch and the second throw terminal of the output switch, the input and output switches being operated in common such that either both switches connect to their respective first throw terminals or both switches connect to their respective second throw terminals, and such that the switches are not operated with one switch connected to its first throw while the other switch is connected to its second throw.