Abstract: A ring detect circuit is shown that includes a regenerative latch configured to be coupled to a telephone line. The regenerative latch is configured to generate a fast transient signal in response to a ring signal on the telephone line. The latch is coupled to an isolation transformer through a capacitor. The fast transient passes across the capacitor and through the transformer. A comparator detects the fast transient and, responsive thereto, generates a ring detect signal.

Abstract: Disclosed is a switch driver circuit is shown where the circuit can control current driven devices and drive devices across a capacitive barrier. A mode control signal determines whether the circuit is in a current mode or a capacitive mode. In current mode, the circuit provides a current output signal at an output of the circuit in response to a subject signal, such as an ON switch control signal for a hook switch application. In capacitive mode, the circuit provides a clocked output signal at the output of the circuit in response to the subject signal, such that the clocked output signal can pass across a capacitive isolation barrier.

Abstract: An optoisolator device is shown having a die attachment device with a planar surface. A first circuit die has first and second planar surfaces and a first side surface. A receiver circuit and a first photodiode are formed on the first planar surface of the first circuit die, where the first photodiode is electrically coupled to the receiver circuit. The second planar surface of the first circuit die is attached to the planar surface of the die attachment device. A second circuit die has a transmitter circuit that includes a first light emitting diode and is attached to the die attachment device in a position adjacent to the first side surface of the first circuit die. A clear plastic layer is formed on the planar surface of the die attachment device over the first and second circuit dies. An opaque layer may be formed over the clear plastic layer.

Abstract: The invention relates to a system of two-way packet-oriented serial communication between master and slave. Messages 20, 30 include status and request words 22, 32 which indicate the status of master and slave. Each of the master and slave determines from these words 22,32 separately whether communication is to continue from master to slave, from slave to master, both, or neither.

Abstract: A circuit and method for differential slope demodulator circuit are shown that utilize amplitude stabilizing of a frequency modulated signal to obtain an amplitude stabilized signal. Also shown is bandpass filtering of the amplitude stabilized signal for a first frequency that is offset by a shift frequency below an intermediate frequency, to obtain a first filtered signal and bandpass filtering the amplitude stabilized signal for a second frequency that is offset by the shift frequency above the intermediate frequency, to obtain a second filtered signal. The circuit and method further operate by detecting an envelope of the first filtered signal to obtain a first envelope signal, detecting an envelope of the second filtered signal to obtain a second envelope signal, and differencing the first and second envelope signals to obtain a demodulated output signal.

Abstract: A circuit and method for emulating a component in a circuit are shown that control a current controlled oscillator with a first current that is proportional to a square of a load current of the component and also charge and discharge a high precision capacitor using the current controlled oscillator. The oscillations of the current controlled oscillator are counted to obtain a count value, which is transformed to a transformed current signal using a predetermined transfer function. The transformed current signal is subtracted from the first current that controls the current controlled oscillator. The transformed current signal is subtracted from a second current that is proportional to a square of the load current to determine whether the count value is incremented or decremented responsive to the oscillations of the current controlled oscillator.

Abstract: A clear channel assessment procedure is described. The procedure includes setting a threshold value of signal strength. When a message is ready to transmit, the received signal strength intensity (RSSI) is measured, and compared with the threshold. If the received signal strength is less than the threshold value, the message is transmitted, otherwise the system waits before trying again. After a predetermined number of failed attempts the threshold value is increased. The threshold value may be reduced if no acknowledgement is received.

Abstract: A resonator circuit is shown that is fabricated with substantially identical elements disposed symmetrically along an axis such that the circuit has a linear response to bias current. The alignment of the circuit permits multiple characteristics of the circuit to be calibrated.

Abstract: Disclosed is a filter circuit assembly that includes a filter stage with a variable resistor and a resistor/capacitor (RC) oscillator. A controlling output of the RC oscillator controls the value of the variable resistor. The RC oscillator itself also includes a variable resistor. The controlling output of the RC oscillator also controls the value of the variable resistor of the RC oscillator. The structure of the variable resistor of the filter stage is substantially the same as the structure of the variable resistor of the RC oscillator.

Abstract: Disclosed is a circuit and method for automatic tuning of a resonant circuit in a transceiver having a receiver and a transmitter that includes a power amplifier for driving the resonant circuit. During a transmit mode of the transceiver, a resonance voltage of the resonant circuit is compared to an input voltage signal to the power amplifier to determine an error signal that is converted into a control word. The control word drives an adjustable capacitance bank that is part of the resonant circuit. During a receive mode of the transceiver, the control word value is held constant to substantially maintain resonance of the resonant circuit during operation of the receiver.

Abstract: The present invention is directed toward a system and apparatus for digitally controlling a bias control signal for at least one transistor. The present invention provides for software writable registers that control the bias control signal. The present invention further provides for the bias control signal to be temperature compensated based upon a temperature signal and a temperature profile stored in software writable registers. The present invention further provides for software control of the initialization and configuration of the bias control signal through stored program control of the values in the software writable registers.

Abstract: A shared voltage reference circuit for a codec is shown that includes a voltage reference circuit for producing a reference voltage. A first sample and hold circuit has a first capacitor coupled to an output of the voltage reference circuit through a first switch controlled by a first phase of a sample clock signal for the codec. A second sample and hold circuit has a second capacitor coupled to the output of the voltage reference circuit through a second switch controlled by a second phase of the sample clock signal. A clock generator circuit generates the first and second phases of the sample clock signal, where the first and second phases are non-overlapping.

Abstract: A hook switch circuit is shown wherein two high-voltage bipolar transistors, a PNP transistor Q1 and a NPN transistor Q2. that are connected in a regenerative feedback manner to form a bi-stable latch. The regenerative structure permits the use of low beta transistors that may be turned on with a low control current, but still conduct a sufficient off-hook current. Also shown is a polarity steering regenerative switch (MP1, MP2) that provides a power supply voltage from a telephone line pair and may be adapted for a polarity signal and can be combined with a current mirror (MP7) to produce a current signal proportional to the line voltage (LV1).

Abstract: A method and circuit are shown for generating a higher order compensated bandgap voltage is disclosed, in which a first order compensated bandgap voltage and a linearly temperature dependent voltage are generated. Thereafter, a difference between the linearly temperature dependent voltage and the first order compensated bandgap voltage is generated. The resulting difference voltage is squared, and finally the squared voltage is added to the first order compensated bandgap voltage, resulting in a higher order compensated bandgap voltage. There is also disclosed a higher order temperature compensated bandgap circuit.

Abstract: A level of trust is determined based on a combination of scores for one or more successful authentications. Scores indicate relative degrees of reliability for authentications, so that differing authentication methods may correspond to different scores. The determined level of trust can then be used to allow or deny access to a resource, and can be used to specify the type of access that is allowed, if applicable.

Abstract: A low-voltage supply low-power variable gain amplifier is shown that includes an input control circuit for receiving input signals, a variable gain amplifier (VGA) coupled to the input control circuit, and a circuit output terminal. A differential transconductor is interposed between the input control circuit and the VGA. The VGA amplification of the differential transconductor output is controlled by a gain control voltage signal. A differential amplifier is interposed between the input control circuit and the differential transconductor, where the differential amplifier receives and amplifies the input signal to produce an amplified input signal. An output filter is interposed between the VGA and the circuit output terminal.

Abstract: Disclosed is a circuit and method for continuous automatic tuning of a resonant circuit. A resonance voltage of the resonant circuit is phase shifted by a predetermined phase shift ? degrees and an input voltage signal to a power amplifier driving the resonant circuit is phase shifted by ?±90 degrees to place the signals in quadrature. The phase shifted signals are mixed to obtain a error signal. The error signal is compared to a predetermined voltage range in order to generate control signals for a control word generator, such as an up-down counter. The control word generator produces a control word that drives a capacitance bank that is part of the resonant circuit. The present invention continuously automatically adjusts the capacitance of the capacitance bank to tune the resonant circuit.

Abstract: The present invention is directed toward a method and apparatus for transferring data across an isolation barrier using high speed analog encoded signals. A line side circuit interfaces with tip and ring contacts on one side of a capacitive isolation barrier that isolates the line side circuit from a modem side circuit. During an on-hook state, the line side circuit converts an analog line side voltage signal to a frequency signal and then encodes the frequency signal into a high frequency pulse-width-modulated (PWM) signal. The high frequency PWM signal is transmitted across the capacitive isolation barrier to the modem side circuit. During an off-hook state, the analog line side voltage is again encoded into a high frequency pulse-width-modulated (PWM) signal for transmission across the isolation barrier. The modem side circuit recovers the transmitted PWM signal and converts it into a digital count value that represents the amplitude of the analog voltage observed at the tip and ring.