AN AMPLIFIER STAGE HAVING A SWITCHABLE GAIN AND REDUCED DISTORTION

摘要

An amplifier stage comprising a differential pair (T1, T2) is provided with a resistive ladder (R1...R2n) coupled between the second control electrodes of said differential pair. Taps on mirror positions along the resistive ladder (R1...R2n) are switchably connected to first and second current source transistors (T3, T4), said current source transistors having their control electrodes connected to the first main electrodes of the transistors forming the differential pair. By placing the switches in series with the current source transistors (T3, T4), the influence of the non-linear impedance of the switches is reduced to negligibly small proportions as the output impedance of the current source transistors (T3, T4) is considerably higher than the impedance of the switches. Thus a linear conversion impedance is obtained, resulting in an amplifier stage having a switchable gain and reduced distortion.