Distortion-free limiter for a power amplifier
AssigneeFord Motor Company
InventorsGerald D. Neely, Alfonso Molinar, Andrew C. Krochmal, Robert T. Zeff
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Abstract
A distortion limiter for limiting the amount of distortion of an inverting amplifier is disclosed. A comparator produces a pulse when a signal level at an inverting input of the inverting amplifier exceeds a reference voltage level. The pulse charges a capacitor. When the charge on the capacitor is sufficient to raise the gate voltage of a junction field-effect transistor (FET) above cutoff, the FET shunts the input signal to reduce its level. The distortion characteristics can be controlled by using a voltage divider to adjust the voltage across the FET. A bias voltage at the gate of the FET, keeps the FET turned off when the inverting amplifier is not clipping.
Claims11
A distortion limiting amplifier for amplifying a variable-level input signal, comprising:
- an inverting amplifier having an inverting input and a non-inverting input, wherein said inverting input is configured to receive said input signal and said non-inverting input is connected to a first reference voltage;
- a comparator, having a first input coupled to said inverting input of said inverting amplifier, configured to generate a pulse when a signal level at said inverting input exceeds a second reference voltage supplied to a second input of said comparator;
- an integrator, coupled to an output of said comparator, for storing a charge in response to said pulse produced by said comparator;
- and
- gating means, coupled between said inverting input and ground, having a gate coupled to said integrator, and held below cutoff by a bias voltage at said gate, for attenuating an input signal when said stored charge causes the gate voltage to exceed a cutoff voltage of said gating means.
A distortion limiting apparatus for use with an inverting amplifier, comprising:
- a comparator, coupled to an inverting input of the inverting amplifier, for comparing an input voltage at said inverting input to a reference voltage and for producing a pulse when the level of said input voltage exceeds the level of said reference voltage;
- an integrator, coupled to an output of said comparator, for storing a charge in response to said pulse produced by said comparator;
- gating means, coupled between said inverting input and ground, having a gate coupled to said integrator, and held below cutoff by a bias voltage at said gate, for attenuating an input signal when said stored charge causes the gate voltage to exceed a cutoff voltage of said gating means.
A method of limiting clipping of an inverting amplifier, comprising the steps of:
- (a) comparing a signal level at an inverting input of said inverting amplifier to a reference voltage and generating a pulse when said signal level exceeds said reference voltage level;
- (b) storing a charge in response to said pulse generated in said step (a);
- and
- (c) shunting a portion of the input signal to ground through a gating means when said stored charge causes a gate voltage of said gating means to rise above cutoff.
Dependencies are inferred from the claim text.