A low noise single ended input/differential output rf amplifier

摘要

An amplifier, suitable for RF applications, has good noise properties because of a special configuration of transistors 201 - 203. Transistors 201 and 202 are connected in a cascode configuration, to overcome the Miller effect. Transistors 202 and 203 have their bases driven by a common current source. The main current paths from ground to each of output terminals 221, 222 are essentially noise free. Transistor 201, acting as a transconductance amplifier, does introduce some noise though this is minimised by the use of an inductor 210. Transistor 304 forms a current source for the current path to output terminal 222. A differential output is achieved at terminals 221, 222 by way of transistors 202, 203 having complementary outputs. In another embodiment (Figure 4, not shown), a capacitor is connected across the collector and base electrodes of transistor 202 to introduce a further stage of gain.