High speed, low distortion amplifier design and method

A high speed, low distortion amplifier implemented with all npn bipolar transistors, comprising:

• a differential first stage comprising a first branch that consists of an input npn transistor having its base connected to receive an input voltage, its collector connected in circuit with a positive voltage bus and its emitter connected to supply current to a first stage current source, and a second branch that is also connected to supply current to said first stage current source,
• a current source resistor connected between a positive voltage bus and the second branch of said differential first stage to supply current to said second branch,
• an output terminal,
• an output npn transistor having its collector connected in circuit with a positive voltage bus, its emitter connected in circuit with said output terminal, and its base connected in circuit with said current source resistor, and
• an npn bipolar transistor current correction circuit connected to divert a portion of the current through said current source resistor away from the second branch of said differential first stage, the amount of current diverted by said current correction circuit varying negatively with said input voltage so as to substantially reduce the variations in said second branch current as a function of the input voltage.

A method of reducing distortion in a high speed amplifier, the amplifier including:

• a differential first stage comprising a first branch that consists of an input npn transistor having its base connected to receive an input voltage, its collector connected in circuit with a positive voltage bus and its emitter connected to supply current to a first stage current source, and a second branch that is also connected to supply current to said first stage current source,
• a current source resistor connected between a positive voltage bus and the second branch of said differential first stage to supply current to said branch, the voltage across said resistor varying negatively with said input voltage, and
• an output stage connected to produce an output in response to said input stage,
• said method comprising:
• sensing said input voltage, and
• supplementing the current provided from said current source resistor to said second branch of the first stage by an amount that varies positively with said input voltage, to substantially reduce the variation in the second branch current that would otherwise result from variations in the voltage across said current source resistor as said input voltage varies.