Abstract: In a gain-controlled amplifier, first, second and third transistors are provided, and a signal at one of input and output terminals is compared with a threshold voltage. When the compared signal is lower than the threshold, the second and third transistors are respectively turned into conducting and non-conducting states, and when the compared signal is higher than the threshold, the situation is in reverse. When the third transistor is non-conducting, the first and second transistors are configured to form a cascode amplifier between the input and output terminals to produce a low-noise, high-gain output signal. When the second transistor is non-conducting, the first and third transistors are configured so that the third transistor forms a base-grounded amplifier between the input and output terminals and the first transistor forms a diode for supplying a DC bias current to the third transistor to produce a low-distortion, low-gain output signal.

Abstract: In a gain-controlled amplifier, first, second and third transistors are provided, and a signal at one of input and output terminals is compared with a threshold voltage. When the compared signal is lower than the threshold, the second and third transistors are respectively turned into conducting and non-conducting states, and when the compared signal is higher than the threshold, the situation is in reverse. When the third transistor is non-conducting, the first and second transistors are configured to form a cascode amplifier between the input and output terminals to produce a low-noise, high-gain output signal. When the second transistor is non-conducting, the first and third transistors are configured so that the third transistor forms a base-grounded amplifier between the input and output terminals and the first transistor forms a diode for supplying a DC bias current to the third transistor to produce a low-distortion, low-gain output signal.