Abstract: A completely tunable second order low-pass filter with minimal active circuitry is disclosed. The filter provides a very flexible choice of filter parameters such as cutoff frequency, DC gain, and Q factor, by selecting appropriate resistor values for a single integrated circuit with much lower capacitance, capacitance ratio, and active circuitry than other standard low-pass circuit configurations.

Abstract: Circuits and techniques for controlling gain while performing analog frequency-selective filtering of electronic signals are provided. In particular, these circuits and techniques control gain and filter electronic signals in a way that significantly reduces input-referred noise as the gain increases to accommodate smaller input signals, while operating within reasonable power constraints and employing a minimum amount of die space. Such circuits also significantly reduce the circuitry necessary for performing the combined steps of controlling gain and doing analog frequency-selective filtering of electronic signals.

Abstract: A switched capacitor lowpass filter is disclosed having four cascaded general purpose switched capacitor active filter blocks that combine with each other to produce a particular overall transfer function that has high gain selectivity and substantially linear phase response characteristics. The filter can also include a clock input which allows a user to select the cut-off frequency of the filter. The filter's characteristics are tailored in accordance with a method which: (1) introduces a notch frequency into the filter's gain characteristics, so as to improve the filter's gain selectivity near the cut-off frequency, and (2) linearizes the phase response characteristics of the overall filter, without modifying the magnitude of the gain of the notch-containing filter.

Abstract: Disclosed is a switched capacitor filter block having a nonlinear quality coefficient, Q, whereby quality can be enhanced while limiting the size of feedback resistors in the filter block. A pair of capacitors alternately switchably connect an input signal to the input of integrator whereby the sampling frequency is twice the switching frequency. The filter block is readily fabricated in a monolithic integrated circuit with the feedback resistors being thin-film resistors formed on the surface of the monolithic integrated circuit. Such a circuit configuration is more accurate in programming and requires only one mask step in fabrication to program.

Abstract: A switched capacitor filter having DC gain accuracy and low DC offset includes an operational amplifier with a resistor (or switched capacitor) connecting one input of the operational amplifier to a signal input terminal. A first capacitor provides a first feedback loop between the output and an input of the operational amplifier, and an active network is serially connected with another resistor (or switched capacitor) as a filtered feedback loop.