A Low-noise Wideband Variable-gain Amplifier Using An Interpolated Ladder Attenuator

A pervasive thread in implementing voltage-controlled amplifiers has been the use of nonlinear circuit elements directly in the signal path. For example, wide-band variable-gain amplifiers often invoke the exponential lc-Vbe relationship in a bipolar junction transistor to implement a controlled current-fork or a translinear multiplier core. The nonlinear behavior of field-effect transistors has also been widely exploited in this field. All such circuits exhibit various types of residual signal-path nonlinearity (harmonic and intermodulation distortion) caused by non-ideal aspects of transistor behavior and the necessity for "open-loop" design. Furthermore, distortion and noise performance is often degraded by the use ofV-I stages at the input, and the AC and transient response may vary considerably with gain.