Patent ID: 8217715
Filing Date: 2012-07-10
Classification: H03H

Abstract:
1. An active poly-phase filter comprising: an input converting section that receives unbalanced high-frequency power and converts the unbalanced high-frequency power into a converted difference output denoting a difference between a first output and a second output having a phase opposite to a phase of the first output, the first and second outputs being set at a predetermined frequency together; and a poly-phase filtering section, having two first input terminals, two second input terminals and four output terminals, which receives a first input of a difference input at the first input terminals, receives a second input of the difference input at the second input terminals, and outputs a first difference output denoting a difference between two outputs at two of the output terminals and a second difference output denoting a difference between two outputs at the other two output terminals such that phases of the first and second difference outputs differ from each other by π/2 radians, wherein the input converting section has a constant current source, a first transistor, a second transistor, a third transistor, a fourth transistor and a fifth transistor, the unbalanced high-frequency power is received at an emitter of the first transistor, a base and a collector of the second transistor and a base of the third transistor, the first, second, fourth and fifth transistors form a translinear circuit by connecting the constant current source with a base of the first transistor and a base and a collector of the fourth transistor, connecting an emitter of the fourth transistor with a base and a collector of the fifth transistor, and setting an emitter of the second transistor and an emitter of the fifth transistor at a common voltage level, an emitter of the third transistor is set at the common voltage level, the second and third transistors form a current mirror circuit, the first input terminals of the poly-phase filtering section are connected with a collector of the first transistor to receive the first output of the converted difference output of the input converting section as the first input of the difference input at each of the first input terminals, and the second input terminals of the poly-phase filtering section are connected with a collector of the third transistor to receive the second output of the converted difference output of the input converting section as the second input of the difference input at each of the second input terminals.