MULTIPLE STAGE HIGH DYNAMIC RANGE VARIABLE GAIN AMPLIFIER

摘要

Variable gain amplifiers comprised of multiple variable gain stages, wherein the gain of the various stages is controlled by comparisons of a control voltage with various reference voltages, in the preferred embodiment generated by the use of a series connectin of multiple resistors connected to a supply voltage. These relative comparisons control current ratios determining the gain of each variable gain amplifier stage. By staggering the changes in current ratios, an overall gain change with control voltage which is smooth in gain in dB versus control voltage in volts may be achieved, generally without requiring use of current sources which are proportional to absolute temperature. The sequence of control of the individual gain states as a function of the control voltage in the preferred embodiment is selected such that the best performance is obtained with respect to noise, signal handling capability and distortion at every setting of the total gain. This implies that as a function of a decreasing control voltage (or as a function of a decreasing total VGA gain from a maximum gain), first the last amplifier VGA2 is controlled to lower gain values, whereafter the middle amplifier VGA3 is controlled to lower gain values, whereafter the input amplifier VGA1 is controller to lower gain values, whereafter the last amplifier VGA2 is controlled again to still lower gain values.