![]() ![]() A typical transfer function for a differential transistor pair. The usual way of extracting this transfer function is via an integrated transconductance amplifier. What you need to know for the equation to make sense is that an ordinary bipolar differential pair has tanh for a transfer function, basically the difference of the two collector currents. Similarly, just as tangent = sine/cosine, tanh = sinh/cosh. Just as the points (cos t, sin t) form a circle with a unit radius, the points (cosh t, sinh t) form the right half of the unit hyperbola. Most engineers probably don’t encounter hyperbolic functions too often, so here’s a simple overview: Hyperbolic functions are analogs of the ordinary trig functions but are defined using the hyperbola rather than the circle. So a brief review of the relationship’s origin might be worthwhile. The statement is correct but may come as news to engineers who learned about transistor operation via the classic hybrid-pi or Ebers-Moll model in that there is no mention of hyperbolic functions in either one. Where I O is the differential pair tail current, V IN is the differential input voltage, and V T is the thermal voltage, which is about 26 mV at room temperature. ![]() We know that the transconductance of a differential pair of transistors is defined as: Specifically, the authors start out saying: Published monthly since 1967 and now done online, Analog Dialogue covers circuits, systems, and software for signal processing that relate to ADI chips.Ī feature in Analog Dialogue recently caught our eye because it covered some interesting territory relating to the generation of sine waves from triangle waves using a differential pair of transistors. Analog Dialogue is a free technical magazine from chip makers Analog Devices Inc. ![]()
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