A two-terminal current source using the basic circuit of Figure 1a can be enhanced by adding on an independent subcircuit that uses degeneration of a PNP transistor to achieve zero temperature coefficient (tempco or TC). This low-cost design is the result of collecting data on many semiconductor devices over a 15+ year period and frequent reviews of the data. ("Degeneration" is the insertion a resistor in series with the emitter, which decreases the gain of the amplifier but improves attributes such as linearity and input impedance.)...
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