Second order predistortion circuit
AssigneeGeneral Instrument Corporation
InventorShutong Zhou
Life of this patent
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Abstract
A predistortion generator for coupling in-line with a non-linear device produces an output predistortion signal of useful amplitude, but with low composite triple beat and cross modulation distortions. The predistortion circuit comprises a distortion circuit which utilizes the non-linear current flowing through at least one diode, to provide a desired amount of signal attenuation bandwidth. The distortion generator circuitry is always matched to the non-linear device, thereby ensuring a frequency response that is predictable and predefined.
Claims14
A distortion amplifier for generating a selectively distorted RF signal, including an RF amplifier and a distortion circuit;
- the distortion circuit consists of:
- a first signal path, for conducting both RF and DC bias current, including at least one nonlinear device;
- a second signal path, for conducting both RF and DC bias current, coupled in parallel to said first signal path with respect to RF current, coupled in series to said first signal path with respect to DC bias current, and including at least one resistance means;
- and
- a DC bias current input for providing said DC bias current to said first and second paths
- wherein approximately one-third to one-half of the current output from the RF amplifier flows through said first path, and
- wherein the nonlinear device in the first signal path is the sole nonlinear device affecting the level of distortion output by said distortion circuit.
A distortion control circuit coupled between an RF amplifier and a laser transmitter for selective modulation of the RF signal output from the RF amplifier, said distortion control circuit consists of:
- a first signal path comprising a non-linear circuit having at least one diode;
- a second signal path comprising a DC bias current input coupled with a capacitor;
- wherein said first and second signal paths are coupled in parallel between said RF amplifier and ground,
- wherein the RF current from the RF signal flows through both said first signal path and said second signal path, and wherein between approximately one-third to one-half of the RF current flows through said first signal path, and
- wherein the nonlinear circuit in the first signal path is the sole nonlinear circuit affecting the level of distortion output by said distortion control circuit.
Dependencies are inferred from the claim text.