National Semiconductor Corporation

Spreadtrum Communications Corporation

Brian C Martin

Lawrence Jarrett Malone

A reconfigurable baseband filter for use in a multimode communication system is disclosed. One or more filter elements can each be configured as a plurality of sub-elements. The value of each of the filter elements can be varied by switching between at least two of the plurality of sub-elements. Switching noise within a desired passband can be reduced by switching at a rate that is greater than the desired passband. The switching noise in the passband can be further reduced by pseudo-randomly switching between the sub-elements. The filter can use a delta-sigma modulator to generate a pseudo-random switching signal.

Reconfigurable baseband filter

A resistor tuning network is disclosed that comprises a first resistor connected in parallel with a second variable resistor and a third resistor coupled in series with the first resistor and the second variable resistor. The second variable resistor comprises an R-2R ladder network having an input and first and second output terminals, with a first line having a plurality of first arms connected in series with the input and first output terminal and nodes between each pair of arms, each arm having an identical resistor R. A series of shunt arms, each with a 2R resistor and a switch, are selectively connected between the respective nodes and the first or second output terminal. The resistance of the resistor tuning network is tuned by varying the switch positions in the shunt arms in the R-2R ladder network.

Resistor tuning network and method for tuning a resistor in an electronic circuit

A resistor tuning network for an RC filter has a first, fixed resistor and a second, variable resistance connected in parallel with the fixed resistor. The variable resistance is an R-2R ladder circuit having an input and first and second output terminals, with a first line having a plurality of first arms connected in series with the input and first output terminal and nodes between each pair of arms, each arm having an identical resistor R. A series of shunt arms are selectively connected between the respective nodes and the first or second output terminal. Each shunt arm has a 2R resistor and a switch in series, and each switch has 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. The overall resistance is tuned by varying the switch positions in the ladder circuit.

Resistor tuning network and method for microelectronic RC-based filters

An apparatus is disclosed for implementing a complex filter of the type represented by a transfer function having a complex pole. The apparatus is capable of creating real and imaginary parts, Y and Y , of a complex output signal in response to receiving real and imaginary parts, X and X , of a complex input signal. The apparatus comprises a plurality of variable resistors that may be tuned to adjust various operating parameters of the complex filter.

Efficient implementation of a complex filter with on chip resistor tuning

A Sallen-Key filter circuit having an operational amplifier of unity gain is tuned by replacing a resistor of the circuit with an adjustable resistor ladder network. The ladder network has an input and first and second output terminals and a plurality of arms connected in series between the input and first output terminal. Each arm has 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 controls connection of the respective shunt arm to the first or second output terminal, such that the resistance of the ladder network is varied dependent on the switch positions. The first output terminal is connected to the amplifier output and the second output terminal is connected to the amplifier positive input.

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Carlsbad, CA, United States of America

Brian C Martin