Patent ID: 7075369
Filing Date: 2006-07-11
Classification: H03F

Abstract:
1. A variable gain amplifier, comprising: a voltage-current conversion circuit configured to output a first positive current and a first negative current in proportion to a positive input voltage and a negative input voltage, respectively; a variable gain unit configured to supply four output currents obtained by processing the first positive current and first negative current controlled by a gain factor A (0<A<1) controlled by a control signal, wherein the four output currents include a second positive current obtained by multiplying the first positive current by a factor A, a third positive current obtained by multiplying the first positive current by a factor (1-A), a second negative current obtained by multiplying the first negative current by the factor A, and a third negative current obtained by multiplying the first negative current by the factor (1-A); a voltage output unit configured to output a positive output voltage and a negative output voltage by selectively inputting either the second positive current and the second negative current or the third positive current and the third negative current; and a common-mode feedback unit configured to provide a feed-back loop through the voltage output unit using a voltage difference between the positive and negative output voltages and an external reference voltage.