Patent ID: 7193455

Claim:
A programmable/tunable active RC filter, comprising: a first field effect transistor device composed of a first field effect transistor component and a second field effect transistor component, wherein each gate of said first field effect transistor component and said second field effect transistor component is respectively connected to a first voltage source and a second voltage source, and a first endpoint of said first field effect transistor component is connected to a first endpoint of said second field effect transistor component; a second field effect transistor device composed of a first field effect transistor component and a second field effect transistor component, wherein each gate of said first field effect transistor component and said second field effect transistor component is respectively connected to said first voltage source and said second voltage source, and a second endpoint of said first field effect transistor component is connected to a second endpoint of said second field effect transistor component, and said first endpoint of said first field effect transistor component of said second field effect transistor device is connected to said second endpoint of said first field effect transistor component of said first field effect transistor device; a differential amplifier having two input terminals and two output terminals, wherein each of said two input terminals is respectively connected to said second endpoint of said second field effect transistor component of said first field effect transistor device, and said first endpoint of said second field effect transistor component of said second field effect transistor device; two first variable resistors R f , wherein one end of each said two first variable resistor is respectively connected to said output terminals of said differential amplifier, another end of each said two first variable resistor is respectively connected to said first endpoints of said first field effect transistor devices and said second endpoints of said second field effect transistor devices; two second variable resistors R p , wherein one end of each said two second variable resistor is respectively connected to a first signal input terminal and a second signal input terminal, and another end of each said two second variable resistor is respectively connected to another end of said two first variable resistors; and two capacitors, wherein each of said two capacitors is respectively connected to said two input terminals and said two output terminals of said differential amplifier for forming said active RC filter and then being outputted from two output terminals of said two capacitors.