Patent ID: 6407627
Filing Date: 2002-06-18
Classification: H03H

Abstract:
A filter circuit assembly, comprising:a filter circuit including an operational amplifier connected in unity gain, the amplifier having a positive input, a negative input, and an output; and at least one adjustable resistor connected in series with the amplifier input, the adjustable resistor comprising a resistor ladder network, the ladder network having an input and first and second output terminals, a plurality of arms connected in series between the input and first output terminal, each arm having a resistor R and a node separating each pair of adjacent arms, a shunt arm connected to each node, each shunt arm having a resistor which has a value which is a multiple of R and a switch in series, each switch having a first, closed position connecting the shunt arm to the first output terminal and a second, open position connecting the shunt arm to the second output terminal, such that the resistance of the ladder network is varied dependent on the switch positions and is at a maximum value when all switches are closed and a minimum value when all switches are open, whereby a resistance can be tuned by varying the switch positions in the ladder circuit, the first output terminal being connected to the amplifier output and the second output terminal being connected to the amplifier positive input.