Amplifier with low input impedance

摘要

The amplifier (CD) comprises two transistors (T1,T2) connected in series between a supply voltage terminal (VCC) and the ground, and the third transistor (T3) in the current mirror configuration with the second transistor (T2). The collector ofthe first transistor (T1) is connected to the base of the second transistor (T2) and forms the input (IN) of the amplifier. The base of the first transistor (T1) is connected to a reference potential, which is the supply potential (VCC). A resistor (R1) is inserted between the supply voltage terminal and the collector of the first transistor (T1). The collector of the third transistor (T3) forms the output (OUT) of the amplifier. In the second embodiment, the third transistor is connected as followre whose base is connected to the collector of the second transistor; an additional resistor is inserted between the first and the second transistors. A symmetric amplifier in the first embodiment comprises two pairs of transistors connected in series with resistors between the supply voltage terminal and the ground with an inserted current source, and two transistors in current-mirror configurations with the corresponding transistors of the two pairs. A symmetric amplifier in the second embodiment comprises additional resistors inserted between the two transistors of each pair, and two transistors forming a differential output pair with a separate current source. A switching matrix is claimed which has N inptus and P outputs laid out so that each output can be connected to each input by at least one current path comprising at least one amplifier.