A communications system includes a transmission channel in which, for efficiency, a processor such as an amplifier is operated in a nonlinear mode. When the signal is modulated in a manner which is affected by the nonlinearity of the processor, such as a multicarrier modulation, a distortion lineari
A communications system includes a transmission channel in which, for efficiency, a processor such as an amplifier is operated in a nonlinear mode. When the signal is modulated in a manner which is affected by the nonlinearity of the processor, such as a multicarrier modulation, a distortion linearizer is used. The distortion linearizer incluees the source-to-drain conductive channel of a FET. The gate of the FET is coupled to ground by an impedance which may be a low inductance, and the gate is biased relative to the channel, possibly near pinchoff, to cause the channel to exhibit desirable gain expansion and phase shifts in response to signal input level, which are selected to compensate the distortion of the nonlinear processor. When the signal is modulated in a manner which is not significantly affected by the nonlinearity of the processor, as for example frequency modulation, the distortion linearizer is switched to a linear or ON mode, in which the amplitude and phase are invariant with signal level. The switching is accomplished by adjusting the gate-to-channel voltage.
대표청구항▼
A switchable distortion generator for, within a particular frequency range, distorting at least one of (a) amplitude and (b) phase of signal to be distorted, in response to the amplitude of said signal to be distorted, said circuit comprising: a FET including a gate electrode, and also including sou
A switchable distortion generator for, within a particular frequency range, distorting at least one of (a) amplitude and (b) phase of signal to be distorted, in response to the amplitude of said signal to be distorted, said circuit comprising: a FET including a gate electrode, and also including source and drain electrodes and a controllable path for the flow of signal therebetween; impedance means coupled between said gate electrode and a point of reference potential, said impedance means being selected to have a range of values, within said frequency range, for coacting with a bias for controlling said FET for distortion of said signals traversing said controllable path; inductance means including first and second ends; first coupling means coupled to said inductance means and to said FET, for coupling said first end of said inductance means to said source electrode and said second end to said drain electrode, for providing a path for flow of said signal parallel to said controllable path; switchable bias generating means coupled to said gate electrode, and to said controllable path, for selectively generating a voltage, said voltage being selectable to be one of a fixed first voltage and a second voltage, said first voltage being selected at a value such that, when applied across said gate electrode and said controllable path, causes said FET to become conductive in a substantially linear operating mode, and said second voltage being selectable in conjunction with the value of said reactance means to a value within a range in which, when said second voltage is applied across said gate electrode and said controllable path, said FET operates in a nonlinear mode exhibiting significant nonlinearity to signals traversing said controllable path.
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