Distortion free power limiting and clipping prevention circuit

In an amplifier for increasing the amplitude of an input signal in order to generate a relatively high amplitude output signal, said amplifier being powered by a DC power supply generating positive and a negative DC supply voltages from an AC power input in which the magnitude of said supply voltages may vary to some extent responsive to variations in the voltage of said power input and the magnitude of said output signal, a circuit for limiting the level of said output signal to an output level which is a function of the mangitude of said supply voltage, comprising:

• a voltage controlled attenuator connected to the input of said amplifier for reducing the amplitude of the input signal responsive to an attenuator control signal;
• reference means for generating negative and positive output references which are a function of the magnitude of said negative and positive supply voltages, respectively, such that the magnitude of said negative and positive output references vary in accordance with the variaof the respective negative and positive supply voltages for said amplifier;
• and
• comparator means receiving the output of said amplifier and said negative and positive output references, said comparator means including means for comparing said output signal to said positive output reference when said output signal is positive and for comparing said output signal to said negative output reference when said output signal is negative, said comparator means further including means for generating said control signal when the absolute value ofsaid output signal exceeds the absolute value of a predetermined ratio of the output reference to which said output signal is being compared such that the positive and negative clipping levels of said output signal are independent from each other;
• whereby said amplifier may produce the maximum available power without clipping as the maximum available power varies.

In an amplifier for increasing the amplitude of an input signal in order to generate a relatively high amplitude, bipolar output signal, said amplifier being powered by a DC power supply generating positive and negative DC supply voltages, a circuit for limiting the level of said output signal to a preselected positive output level and a preselected negative output level, comprising:

• a voltage controlled attenuator connected to the input of said amplifier including a light emitting diode/light dependent resistor pair with said resistor shunting said input signal;
• reference means for providing a positive output reference and a negative output reference;
• and
• a first diode having its cathode connected to the anode of a second diode and to the output of said amplifier, a third diode having its anode connected to the cathode of said light emitting diode and the anode of said first diode and its cathode receiving said positive output reference, and a fourth diode having its cathode connected to the anode of said light emitting diode and the cathode of said second diode and its anode receiving said negative output reference such that an output level significantly more positive than a level corresponding to said positive output reference causes current to flow from said output to said reference means sequentially through said second diode, light emitting diode and third diode thereby attenuating the input signal to limit the output level of said amplifier, and an output level significantly more negative than said negative reference causes current to flow from said reference means through said output sequentially through said fourth diode, light emitting diode and first diode, thereby attenuating the input signal to limit the output level of said amplifier.

In an amplifier for increasing the amplitude of an input signal in order to generate a relatively high amplitude, bipolar output signal, said amplifier being powered by a DC power supply generating positive and negative DC supply voltages, a circuit for limiting the level of said output signal to a preselected positive output level and a preselected negative output level, comprising:

• a voltage controlled attenuator connected to the input of said amplifier for reducing the amplitude of the input signal responsive to an attenuator control signal;
• reference means for providing a positive output reference and a negative output reference, said reference means including a first pair of voltage divider resistors connected between said positive supply voltage and ground to generate said positive output reference therebetween and a second pair of voltage divider resistors connected between said negative supply voltage and ground to generate said negative output reference therebetween;
• and
• comparator means receiving the output of said amplifier and said positive and negative output references for comparing said output signal to said positive output reference when said output signal is positive and for comparing said output signal to said negative output reference when said output signal is negative, said comparator means further including means for generating said control signal when the absolute value of said output signal exceeds the absolute value of a predetermined ratio of the output reference to which said output signal is being compared such that the positive and negative clipping levels of said output signal are independent from each other.