An analog
variable gain amplifier (VGA) adjusting a
signal level of a mobile communication
system is provided. More particularly, design of a VGA using an
operational transconductance amplifier (OTA) having a wide linear input / output range is disclosed. The VGA includes two double-differential-pair OTAs and feedback resistors. A first differential input of a first double differential pair OTA receives an input
signal from the forward stage, and a second differential input is negatively fed back through a differential output and a passive
resistor. An input in which a first block of the connection structure and first and second differential inputs of a second double differential pair OTA are connected receives an output
signal of the first block stage. The output is negatively fed back in series through a variable
resistor whose resistance varies exponentially with an adjustment
voltage from outside. According to the VGA, it is possible to provide a characteristic of
linear variation of
gain on a
logarithmic scale with respect to a control
voltage with a simple and inexpensive constitution. In addition, the VGA can be designed for a
low pass filter having a conventional OTA used for a core circuit, and has a
simple circuit structure. Therefore, the VGA is convenient for high integration and low-power design, and thus is appropriate for a terminal
chip and so forth.