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US 5,710,522 AGranted
Amplifier having an active current source
AssigneePass Laboratories, Inc.
InventorNelson S. Pass
Life of this patent
Estimating the term…
Abstract
The present invention is a single-ended Class A gain stage amplifier consisting of an active current source. A feedback path from an output node of the amplifier senses the direction and magnitude of the current going through a load coupled to the output node. The feedback path varies the output of the active current source in accordance with the sensed load current. By so doing, the efficiency of the amplifier of the present invention can be doubled as compared to prior art amplifiers operating in Class A mode. In addition, the present invention amplifier exhibits lower signal distortion.
Claims23
An amplifier for amplifying an input signal comprising:
- a signal input node for receiving said input signal;
- a signal output node;
- an input gain device having a control pin coupled to said signal input node, and further having first and second terminals for current flow therebetween;
- a load-current sensing resistor coupled between said first terminal of said input gain device and said signal output node;
- a first reference voltage terminal coupled to said second terminal of said input gain device for current flow between said signal output node and said first reference voltage terminal;
- an active current source having an current output terminal coupled to said first terminal of said input gain device for current flow from said active current source to each of said signal output node and said first reference voltage terminal;
- and
- a feedback path, coupled between said signal output node and said active current source, for detecting the magnitude and direction of current flow through said load-current sensing resistor;
- said active current source further having a quiescent current flow in the absence of current flow through said load-current sensing resistor;
- said active current source further having a first current flow greater than said quiescent current flow by an amount proportional to the magnitude of a current flow between said load-current sensing resistor and said signal output node flowing in a first direction;
- said active current source further having a second current flow less than said quiescent current flow by an amount proportional to the magnitude of a current flow between said load-current sensing resistor and said signal output node flowing in a second direction.
8 more elements
An amplifier comprising:
- a signal input terminal for receiving an input signal;
- a signal output terminal for providing an output signal;
- a first voltage rail for connection to a first voltage potential and a second voltage rail for connection to a second voltage potential;
- a first transistor having a first electrode coupled to said first voltage rail, and further having a second electrode and a control electrode;
- a second transistor having a first electrode, a second electrode coupled to said second voltage rail, and a control electrode coupled to said signal input terminal;
- a first resistor coupled between said first transistor and said second transistor;
- an output resistor having a first end coupled to said second electrode of said first transistor and a second end coupled to said signal output terminal;
- a biasing transistor having a first terminal coupled to said control terminal of said first transistor, a second terminal coupled to said first end of said output resistor, and a control terminal;
- a pull-up resistor connected between said first voltage rail and said first terminal of said biasing transistor;
- a second resistor coupled between said control terminal of said biasing transistor and second terminal of said first transistor;
- and
- a third resistor coupled between said control terminal of said biasing transistor and said signal output terminal.
9 more elements
A method of operating an amplifier comprising the steps of:
- generating a first current flow;
- directing a portion of said first current flow through each of a first gain device and an output node;
- on a control electrode of said first gain device, receiving a time varying input signal having positive and negative voltage swings;
- during a negative voltage swing of said input signal, reducing the conductance of said first gain device, thereby increasing said portion of said first current flow through said output node;
- during a positive voltage swing of said input signal, sinking a second current flow flowing from said output node to said first gain device;
- sensing an increase in said portion of said first current flow through said output node;
- in response to said sensing said increase, increasing the magnitude of said first current flow in proportion to the magnitude of said sensed increase;
- sensing said second current flow;
- and
- in response to said sensing said second current flow, reducing the magnitude of said first current flow in proportion to the magnitude of said sensed second current flow.
7 more elements
Dependencies are inferred from the claim text.