An amplifier stage having a switchable gain and a reduced distortion,

摘要

Resistor ladder (R1 . R2n) connected between the second control electrodes of the differential pair is provided on the differential pair (T1, T2) containing amplifier stage. The taps in the mirror positions along the resistance ladder R1 . R2n are connected to the first and second current source transistors T3 and T4 so as to be switchable and the current source transistors are connected to the first main electrode of the transistor forming the differential pair And a control electrode. By placing the switch in series with the current transistors T3 and T4 the influence of the nonlinear impedance of the switch is reduced negligible as if the output impedance of the current source transistors T3 and T4 was significantly higher than the impedance of the switch . Thus a linear conversion impedance is obtained and the amplifier stage is switchable in gain and distortion is reduced.