National Instruments Corporation

Paul A Lennous

Alvin G Becker

A variable time constant integrator includes an amplifier configured to generate an output signal, a capacitor coupled to provide feedback to the amplifier, and a variable gain element coupled to the output of the amplifier and to the capacitor. The variable gain element is configured to provide the product of a gain and the output signal to the capacitor. The variable gain element is also configured to receive an indication of a new value of the gain and to responsively set the gain equal to the new value of the gain. Adjusting the gain of the variable gain element adjusts the integrator's time constant.

Adjustable time constant integrator

An AC attenuator system including a compensation circuit for providing a selectable trimming impedance for the AC attenuator. The compensation circuit comprises a plurality of capacitors preferably coupled in parallel with a portion of the attenuator, wherein the capacitors have binary weighted values. The compensation circuit also includes a plurality of switches, wherein each switch is coupled to an input of each of the plurality of capacitors and is further coupled to the AC attenuator circuit. The switches are preferably microelectronic machined system (MEMS) switches. The compensation circuit further includes a memory element coupled to the plurality of switches. The memory element stores a value, preferably a digital or binary value, which is operable to open/close selected switches. The value stored in the memory element is provided to the switches during power on, thereby opening/closing selected switches and configuring a capacitance value among the plurality of capacitors for compensation of the AC attenuator system. The compensation circuit thus produces a selectable trimmer impedance for the AC attenuator.

Automatic compensation of an AC attenuator using a digital to capacitance converter

An electrical power supply is described which includes a floating current source. The floating current source includes a current source providing a selected amount of electrical current to a first terminal, and a current sink receiving the selected amount of electrical current from a second terminal. The current source is adapted for coupling to a first electrical voltage level which is positive with respect to a reference potential. The current sink is adapted for coupling to a second electrical voltage level which is negative with respect to the reference potential. The selected amount of current may be proportional to a reference current flowing through both the current source and the current sink. The current source and sink may each include a pair of transistors coupled together such that a flow of electrical current through one of the pair of transistors produces a proportional flow of electrical current through the other transistor. The electrical power supply may also include two line-powered voltage sources producing the first and second electrical voltage levels. During operation, the first and second electrical voltage levels may be adjusted by varying the first and second voltage sources, and a desired electrical voltage may be developed between the first and second terminals. The power supply is thus capable of supplying a bias voltage and current to an amplified transducer (e.g., an amplified piezoelectric transducer).

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Paul A Lennous