Micro Linear Corporation

David Ritter

Carlos A Laber

Robert Zucker

A two-stage differential to single-ended amplifier. The input stage converts a differential voltage to a differential current. A first pair of bipolar input transistors are biased with constant currents. Therefore, their on-resistance does not affect gain linearity. Changes in input voltages induce currents in a first pair of field effect transistors (FETs) each having a gate coupled to the collector of a corresponding input transistor and a drain coupled to the emitter of the corresponding input transistor. Differential currents are provided to the output stage by a second pair of FETs, each configured to mirror the current in a corresponding one of the first pair of FETs. Gain is adjustable by enabling additional pairs of FETs configured as current mirrors. The output stage includes a second pair of bipolar transistors with bases coupled together and biased with equal currents. Currents from the input stage are applied to the emitters of the second pair of bipolar transistors. A third pair of FETs are coupled to the second pair of bipolar transistors forming a current mirror which tends to equalize the currents from the input stage. A current representative of a sum of currents from the input stage is forced through a resistor, forming the output voltage. The output voltage DC level is adjusted by controlling the voltage at the bases of the second pair of bipolar transistors.

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San Jose, CA, United States of America

David Ritter