Patent ID: 7865087
Filing Date: 2011-01-04
Classification: H03F,H03H,H03K

Abstract:
1. A bandpass filter circuit, comprising: a first transconductance amplifier circuit for converting a differential input voltage into a differential output current; a second transconductance amplifier circuit for converting a differential input voltage into a differential output current; a third transconductance amplifier circuit for converting a differential input voltage into a differential output current; a first common-mode feedback circuit for outputting a first control signal to the first transconductance amplifier circuit so that a D.C. voltage level of a differential output from the first transconductance amplifier circuit is at a predetermined level; a second common-mode feedback circuit for outputting a second control signal to the second transconductance amplifier circuit so that a D.C. voltage level of a differential output from the second transconductance amplifier circuit is at a predetermined level; a first capacitor; a second capacitor; and a third capacitor, wherein: a noninverting input terminal is connected, via the first capacitor, to (i) a noninverting output section of the first transconductance amplifier circuit and (ii) a noninverting input section of the second transconductance amplifier circuit; an inverting input terminal is connected, via the second capacitor, to (i) an inverting output section of the first transconductance amplifier circuit and (ii) an inverting input section of the second transconductance amplifier circuit; a noninverting output section of the second transconductance amplifier circuit is connected to (i) an inverting input section of the first transconductance amplifier circuit, (ii) a noninverting input section and an inverting output section of the third transconductance amplifier circuit, and (iii) one end of the third capacitor; an inverting output section of the second transconductance amplifier circuit is connected to (i) a noninverting input section of the first transconductance amplifier circuit, (ii) an inverting input section and a noninverting output section of the third transconductance amplifier circuit, and (iii) another end of the third capacitor; the noninverting output section of the third transconductance amplifier circuit serves as an inverting output terminal, the inverting output section of the third transconductance amplifier circuit serves as a noninverting output terminal; the noninverting output section and the inverting output section of the first transconductance amplifier circuit serve as input terminals of the first common-mode feedback circuit; and the noninverting output section and the inverting output section of the second transconductance amplifier circuit serve as input terminals of the second common-mode feedback circuit.