Patent ID: 6362691
Filing Date: 2002-03-26
Classification: H03H,H04B

Abstract:
An inductorless monolithic voltage tunable filter circuit comprising:first amplifier means having a first input and a first output, a first input impedance associated with the first input being much less than a first output impedance associated with the first output, the first amplifier means having a voltage gain of slightly less than one, the first amplifier means comprising: a source follower amplifier including a first FET having a gate coupled to the first input, a drain coupled to a power supply and a source coupled to the first output; and a current source having a first terminal coupled to ground and a second terminal coupled to the source of the first FET; second amplifier means having a second input and a second output, a second input impedance associated with the second input being much larger than a second output impedance associated with the second output, the second amplifier means having a voltage gain of greater than one, the second input being coupled to the first output to form a filter input; first phase shifting means coupled to the output of the second amplifier means and the input of the first amplifier means; and second phase shifting means coupled to the filter input, the first amplifier means and the second amplifier means for collectively providing a frequency dependent impedance at the filter input.