Variable-gain amplifier with pseudo-logarithmic gain control for generating two control currents

摘要

Control circuit for generating two control currents for a variable gain amplifier having a gain which is substantially proportional to the ratio of the two control currents. For a gain control which is independent of the signal level of the variable gain amplifier an exponential control characteristic is needed. The control circuit generates a set of control currents 2*I and 2*J with a ratio which is pseudo-exponential dependent on the control parameter uc. The ideal exponential characteristic is approximated to with a second-order function of the type ((1+x)/(1-x))2 by means of a voltage-to-current converter, a first translinear loop and a second translinear loop.