LINEAR-IN-DB, LOW-VOLTAGE, PROGRAMMABLE/VARIABLE GAIN AMPLIFIER (PGA) USING RECURSIVE CURRENT DIVISION

摘要

A Programmable-Gain Amplifier (PGA) has programming steps that are linear when expressed in Decibels (linear-in-dB). A Recursive Current Division (RCD) resistor network (30) generates currents that are selected by programmable switches (34, 44, 54) to connect to a summing node (VS) input of an amplifier (10). A feedback resistor (14) is connected across the summing node (VS) and the amplifier (10) output (VOUT). The resistor network (30) has only three resistance values regardless of the number of currents selectable as programming steps. The value of a third resistor (53) is set equal to the equivalent resistance of a second resistor (32, 42, 52) in parallel with a series connection of a first resistor (31, 41, 51) and the third resistor (53). Each final cell (50) in the resistor network (30) is equivalent to the third resistor (53), allowing recursive division of adjacent currents. The ratio of adjacent currents remains constant for all cells. Recursive Current Division (RCD) produces linear-in-dB programming steps. Floating switches are avoided since switches connect to ground.