Abstract: Many electronic devices, such as computers and printers, communicate data to each other over wireline or wireless communications links. One component vital to such communications is a voltage-controlled oscillator (VCO)—a circuit that outputs an oscillating signal having an oscillation frequency based on a control voltage. Conventional VCOs adjust frequency based on a single control voltage input, which makes them vulnerable to unintended changes in the control voltage (and power-supply voltages relative to the control voltage.) These voltage changes cause frequency deviations that can make communications between devices less reliable. Accordingly, the present inventors devised a VCO that includes differential frequency control—frequency control based on the difference of two control voltages.

Abstract: A delay stage used in a ring-type voltage-controlled oscillator has an inverter, a memory element, and tuning circuitry. The memory element is coupled to the output of the inverter to delay the time before the inverter's output begins to switch states in response to the inverter's input switching states. The tuning circuitry receives a control voltage and is coupled to the inverter to alter the strength of the inverter without altering the strength of the memory element. Altering the strength of the tuning circuitry alters the delay of the delay stage, and hence the frequency of the VCO's operation. Because the strength of the memory element is not altered, the speed at which the inverter's output switches remains substantially constant at all tuned frequencies. The switching speed is primarily dictated by the FT of the process.

Abstract: Circuits and methods that improve linearity with use of cancellation of at least a portion, and preferably, substantially all of, at least one significant harmonic from the output of a primary circuit, e.g., the 3rd harmonic, using the output of a substantially functionally identical auxiliary circuit.

Abstract: A transmitter includes a sensor adapted to sense a process variable and responsively provide a sensor analog output. An analog to digital converter provides a digitized output in response to the sensor analog output within a converter dynamic range. Signal range bracketing circuitry provides a bracketed range of the sensor analog output to the analog to digital converter for conversion. Outputs from the signal range bracketing circuitry and the analog to digital converter together provide a digital representation of the sensor analog output signal.

Abstract: In a hearing aid, undesirable oscillations that are caused by acoustic feedback occur when the gain of the hearing aid amplifier is increased. These oscillations in the hearing aid system response are substantially suppressed by providing phase equalization that equalizes the phase of the microphone, amplifier, receiver and feedback path involved in the hearing aid. The phase equalization can be provided directly in the signal path at the output of the amplifier or by a separate inner loop feedback around the amplifier. The phase equalization can be provided by one or more first or second order filters that operate as an all-pass filter to provide a time delay but do not affect the magnitude of the signal in the audio frequency range.

Abstract: A transmitter includes a sensor for sensing a primary process variable representative of a process, and providing a sensor output current. An integrator in the transmitter integrates the sensor output current. The integrator has an amplifier on an integrated circuit and an off-chip capacitor coupled between the inverting input on the amplifier and the amplifier output via two integrated circuit pads, which leak undesirable leakage current to the integrator. A leakage cancellation circuit is selectively connectable to the inverting input of the amplifier in the integrator, the cancellation circuit providing a current substantially opposite in polarity and equal in magnitude to the leakage current as a function of a stored voltage representative of the magnitude of the leakage current. A microprocessor based compensation circuit compensates the output of the integrator for repeatable errors which affect the process variable.