High output current buffer
First Claim
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1. A high current output buffer comprising:
- a first bipolar transistor with its emitter producing the high output current;
a second bipolar transistor having the same polarity as the first, the emitter of the second transistor connected to the collector of the first transistor, and the collector of the second transistor connected to a first voltage source;
the base of the first transistor coupled to the collector of a third transistor of the opposite polarity with respect to the first and second transistors;
the emitter of the third transistor connected to a first resistor whose distal end is coupled to a second voltage source;
the emitter of the third transistor also coupled to the emitter of a fourth transistor of common polarity with the third transistor;
the collector of the fourth transistor coupled to its base and to a first current source;
the base of the second transistor coupled to a resistor whose distal end is coupled to the second voltage source;
the base of the second transistor also coupled to the emitter of a fifth transistor of common polarity to the third and fourth transistors;
the collector of the fifth transistor coupled to a second current source;
the bases of the fourth and the fifth transistors are coupled together; and
the base of the third transistor coupled to the collector of the fifth transistor, wherein the fourth and fifth transistors form a current mirror, and wherein the third, fourth and fifth transistors form a negative feedback loop, and where any incremental base drive for the first transistor to support an incremental current at the emitter of the first transistor is supplied from the collector of the third transistor.
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Abstract
A bipolar high output current buffer is disclosed using a negative feedback current mirror to supply the base drive to an output transistor. Small quiescent currents are used wherein the buffer demonstrates low quiescent power dissipation. The current mirror supplies the incremental base drive to the output transistor to support high output currents. When the output drive may source or sink the high output currents, two current mirrors may be used, one for each of the source and the sinking circuitry. This invention provides for minimal loss of dynamic range.
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Citations
10 Claims
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1. A high current output buffer comprising:
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a first bipolar transistor with its emitter producing the high output current;
a second bipolar transistor having the same polarity as the first, the emitter of the second transistor connected to the collector of the first transistor, and the collector of the second transistor connected to a first voltage source;
the base of the first transistor coupled to the collector of a third transistor of the opposite polarity with respect to the first and second transistors;
the emitter of the third transistor connected to a first resistor whose distal end is coupled to a second voltage source;
the emitter of the third transistor also coupled to the emitter of a fourth transistor of common polarity with the third transistor;
the collector of the fourth transistor coupled to its base and to a first current source;
the base of the second transistor coupled to a resistor whose distal end is coupled to the second voltage source;
the base of the second transistor also coupled to the emitter of a fifth transistor of common polarity to the third and fourth transistors;
the collector of the fifth transistor coupled to a second current source;
the bases of the fourth and the fifth transistors are coupled together; and
the base of the third transistor coupled to the collector of the fifth transistor, wherein the fourth and fifth transistors form a current mirror, and wherein the third, fourth and fifth transistors form a negative feedback loop, and where any incremental base drive for the first transistor to support an incremental current at the emitter of the first transistor is supplied from the collector of the third transistor. - View Dependent Claims (2, 3, 4)
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5. A high current output buffer comprising:
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a first PNP with its emitter coupled to a first current source, the current source coupled to a positive voltage source, Vcc;
a first NPN with its emitter coupled to a second current source, the second current source coupled to a voltage source less positive than Vcc, this less positive voltage source labeled Vee;
wherein the collector of the first PNP is coupled to Vee, and the collector of the first NPN is coupled to Vcc, and wherein the bases of these transistors are coupled together and are arranged to accept an input signal;
the emitter of the first PNP is coupled to the base of a second NPN and the emitter of the first NPN is coupled to the base of a second PNP, the emitters of the second PNP and the second NPN coupled together to provide an output signal;
a third NPN with its collector coupled to Vcc and emitter coupled to the collector of the second NPN;
a third PNP with its collector coupled to Vee and its emitter coupled to the collector of the second PNP;
a first current mirror with a first input and a first output, each arranged to sink current signals, wherein the first input is coupled to the base of the third PNP and the first output is coupled to the base of the second PNP;
the first current mirror arranged to work near Vee; and
wherein a change in the output signal current is reflected back to the first current mirror that supplies the necessary base drive to the second and third PNP transistors to accommodate the change in the output signal current delivered. - View Dependent Claims (6, 7, 8, 9, 10)
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Specification