Amplifier arrangement whose overall gain is controllable by means of a control voltage
AssigneeU.S. Philips Corporation
InventorManfred Horl
Life of this patent
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Abstract
Volume control circuits generally vary the overall gain of a low-frequency amplifier by varying the gain in a negative-feedback branch. At very high gain, at which very large output signals are obtained, the negative-feedback is then very small, which may produce a non-linear distortion. In accordance with the invention the gain of a frequency-compensation stage is varied so that it increases when the overall gain increases. The loop gain at higher output amplitudes is now higher than it would otherwise be so that non-linear distortion is reduced.
Claims16
An amplifier arrangement comprising a first amplifier having at least one input and an output, a second amplifier having a low-pass frequency characteristic and an input coupled to the output of the first amplfier and an output coupled by means of at least one negative feedback branch to an input of the first amplifier to provide negative feedback, and control voltage means coupled to an input of said first amplifier for varying the negative feedback and thereby the overall gain of the amplifier arrangement, said control voltage means also being coupled to the second amplifier for varying the gain of the second amplifier such that for an increase in the overall gain of the amplifier arrangement the gain of the second amplifier also increases.
An amplifier arrangement comprising at least one differential amplifier including first and second transistors having their emitters interconnected and the collector of the second transistor coupled to an output of the differential amplifier, an input terminal coupled to said interconnected emitters of the first and second transistors for applying an input signal thereto, a variable gain amplifier with a low-pass frequency characteristic and having a signal input coupled to said output of the differential amplifier and an output coupled to an output of the amplifier arrangement and via at least one negative feedback network to said interconnected emitters of the first and second transistors, and means for applying a control voltage to the bases of the first and second transistors and to a gain control input of the variable gain amplifier whereby the control voltage simultaneously varies the gain of the differential amplifier and the gain of the variable gain amplifier thereby to reduce non-linear distortion at a high overall gain of the amplifier arrangement.
A variable gain amplifier arrangement comprising a signal input terminal and a signal output terminal, a first amplifier, a second amplifier having a variable gain and a low-pass frequency characteristic, means coupling said first and second amplifiers in cascade between said signal input and output terminals, a negative feedback circuit coupling an output of the second amplifier to an input of the first amplifier, and a source of variable control voltage coupled to an input of the first amplifier and to a gain control input of the second amplifier thereby to simultaneously vary the effective gain of the first amplifier and the gain of the second amplifier as the control voltage is varied, the control voltage being operative to increase the gain of the second amplifier as it increases the overall gain of the amplifier arrangement.
Dependencies are inferred from the claim text.