Inverting the bipolar differential pair for low-voltage applications

In this paper, the author presents a new bipolar differential transconductor that functions just like an emitter-degenerated differential pair, except for the following: it operates on a low power supply; it has a rail-to-rail common-mode input-voltage range; permits a wide output-voltage swing; has a transconductance gain that is nearly constant with the common-mode input voltage; and requires only n-p-n transistors in the signal path. We describe intuitively how the circuit functions and provide DC measurements from a prototype circuit, breadboarded from a quad TPQ3904 and a thick-film resistor array demonstrating proper operation on a single-ended 1.2-V power supply.