Abstract: A controllable reactance implemented within an integrated circuit includes a first sub-circuit (20) comprising a reactive element, for example a capacitor 12, coupled in series with a transistor (14). A controllable current source (16) injects a controllable bias current through the transistor (14) to vary the effective resistance of the transistor (14) and hence the effective complex impedance of the capacitor combination. A second transistor (18) amplifies the current to increase the effective capacitance. Preferably, a second sub-circuit (24) includes corresponding components (26, 28, 30) to mirror the real component of the current flowing in the first sub-circuit (20), and transistors (32 and 34) to reflect an inverse current to the coupling node line (22) to cancel the real component of the current at the node, to thus simulate a purely capacitive circuit. An oscillator embodying this circuit is also disclosed.

Abstract: A driver circuit has first and second output drivers, monitor circuitry for deriving control signals related to driven signal levels, and supply circuitry responsive to the control signals for controlling the supply voltage to the output drivers. The monitor circuitry can be connected to monitor the voltage at the supply inputs of the output drivers for deriving the control signals. Alternatively, the monitor circuitry can be connected directly to monitor driven output levels from the drivers. In the latter case, the output levels to be monitored are rectified. The monitor circuitry can comprise first and second operational amplifiers for comparing a monitored voltage from first and second output drivers, respectively, to a first and second reference voltages, respectively. The supply circuitry can comprise first and second constant current sources, for example field effect transistors.

Abstract: A differential output circuit has first and second output lines and an output impedance connected between the first and second lines. The output impedance includes an active device (e.g., a field effect transistor) having a control input for receiving a control signal value for controlling the impedance value of the active device. A bias circuit is responsive to a reference impedance element for generating the control signal value for controlling the impedance value of the active device. An output driver stage is connected to the first and second output lines for supplying first and second differential driven output signals to the first and second output lines, respectively. An integrated circuit can include a number of differential output circuits and a common bias circuit responsive to a single reference impedance element for generating the control signal value for controlling the impedance value of each active device.

Abstract: A method and apparatus for rapidly measuring nitrogenase activity of a nitrogen fixing plant growing in a medium in a non-porous container, is described. Gas containing hydrogen is sampled at the surface of the medium at a rate approximately equal to the rate of hydrogen diffusion from the medium, and the sample is passed to a hydrogen sensor where it is measured and nitrogenase activity is determined therefrom.

Abstract: A differential signal receiver circuit includes a first differential stage receiving input differential signals, a second differential stage receiving shifted differential signals and summing stage summing outputs of the first and second differential stages. Preferably the summing stage is formed by a wired-OR connection between the first and second differential stage outputs. The circuit finds application in digital systems for receiving data transmitted between digital equipment.

Abstract: A corrosion limiting device for use with a fluid-carrying piping system having a connection formed from first and second components. A seal is carried by the components for forming a fluid-tight seal between the components. The components form a groove external of the seal. The corrosion limiting device includes an elongate member having first and second end portions and a length sufficient to extend around the groove. At least a portion of the elongate member is adapted to seat within the groove for aligning the elongate member on the components. The first and second end portions of the elongate member are fastened together. The elongate member serves to inhibit corrosion of the connection.

Abstract: A voltage comparator circuit includes a comparator 42 having a first comparison input, a second comparison input and first and second switched current memories 52, 58 (e.g., switched FETs) connectable, respectively, to the first and second comparator inputs for input voltage offset compensation. In use, during a storage phase, a current value is stored in the switched current memory for each of the first and second comparison inputs and, during a comparison phase, the stored current values are used to compensate for voltage offsets between the comparison inputs.

Abstract: A differential delay buffer includes a variable delay buffer unit, the variable delay buffer unit having a differential stage followed by a variable hysteresis stage. A plurality of variable delay buffer units can be cascaded together, in each variable delay buffer units a part of the required delay being effected. The variable hysteresis stage is responsive to the signal level at a second differential stage output to recover the signal at a first differential signal output from the variable delay buffer unit and is responsive to the signal level at a first differential stage output to recover the signal at the second delayed differential signal output for the variable delay buffer unit. The differential delay buffer can be included in a delay locked loop in data transmission applications.

Abstract: An apparatus for analyzing bolt loads which includes first and second flanges having opposed faces. A plurality of bolts extend through the faces for securing the flanges together. A sensor is carried by each of the bolts for measuring the load experienced by the bolt. An output mechanism is coupled to the sensor for permitting the load on one of the bolts to be analyzed relative to the load on another of the bolts.

Abstract: A differential signal receiver circuit includes a first differential stage receiving input differential signals, a second differential stage receiving shifted differential signals and summing stage summing outputs of the first and second differential stages. Preferably the summing stage is formed by a wired-OR connection between the first and second differential stage outputs. The circuit finds application in digital systems for receiving data transmitted between digital equipment.

Abstract: An analog to digital converter has an analog signal input, reference voltage divider and a plurality of comparators. Each comparator has a first input connected to said analog signal input and a reference input connected to receive a respective predetermined reference voltage from the reference voltage divider. In addition, test mode circuitry is provided for feeding a sequence of test voltages from the voltage divider to the first input of the comparators in a test mode. A decoder is connected to an output of each comparator for generating a binary output signal representative of an input analog signal.

Abstract: An apparatus and method for measuring differential oxygen concentration between two flowing gas streams is described. A reference gas and a sample gas in separate gas flow paths are passed, at selected temperature, pressure and flow rate over a respective one of a pair of electrically connected oxygen sensors which produce an output signal proportional to the differential oxygen concentration between the sensors. The output signal may be amplified and recorded by any conventional means. An internal calibration system is also described.

Abstract: An apparatus for electrolytically generating small volumes of a selected gas such as hydrogen for introduction into a flowing gas stream is described. The gas stream flows through an electrolytic cell wherein the selected gas is generated at an electrode and a portion of the gas stream is diverted through a needle valve and a non-conducting capillary with a small orifice to deliver gas to the electrodes so as to dislodge the selected gas bubbles forming thereon and carry them into the flowing gas stream. To maintain the level of electrolyte in the cell, the cell is connected by a narrow tube to a reservoir of electrolyte. The reservoir has a volume and surface area many times greater than that of the cell and the gas volume above the reservoir is maintained at the pressure and composition of the gas stream entering the electrolytic cell.

Abstract: A non-invasive method and apparatus are described for measuring the oxygen concentration in the infected cells of the nodules of nitrogen fixing plants in the laboratory or field. In many cases, this information can be used to estimate the nitrogenase activity, and therefore the nitrogen fixation rate, in these nodules since recent studies have shown that the oxygen concentration limits and controls nitrogenase activity under most environmental conditions. Using the same apparatus, a method to measure nodule respiration and nodule oxygen permeability is also described. The nodule oxygen concentration in the infected cells of nodules is maintained at very low levels and has not been measurable previously by non-invasive techniques.