Abstract: A single bit bandpass analog-to-digital converter has an analog summer, an analog bandpass filter, a single bit quantizer, and a single bit digital-to-analog converter connected in a loop. An input signal to the single bit filter is applied to a plus input terminal of the summer, and the output of the digital-to-analog converter is applied to a minus input terminal of the summer. The output signal from the single bit filter is taken from the output of the quantizer. The bandpass filter is preferably driven by a digital clock running at the same frequency as the quantizer and the digital-to-analog converter. This architecture reduces quantization noise within the passband at the possible expense of increasing it outside the passband. The passband is centered precisely on one-quarter of the clock frequency.

Abstract: An on-board regulated voltage up-convertor for converting a first DC voltage at a first node from an electronic system to a second DC voltage for an integrated device at a second node. The convertor comprises reference generator means for generating a predetermined reference voltage at start-up, voltage regulator means coupled to said first node for regulating said first voltage at a predetermined voltage at a third node, voltage multiplier means coupled to said third node and to said second node for multiplying said predetermined voltage to generate an output voltage substantially equal to said second voltage, feedback means coupled to said second node for feeding said output voltage back to said voltage regulator means to adjust the level of said predetermined voltage at said third node according to how said output voltage is relative to said second voltage.

Abstract: A circuit for converting a system supply voltage having one of two levels to a voltage for use by an integrated analog circuit connected to the system upon power-up. The circuit uses a diode-connected transistor to generate a reference voltage necessary for a regulator to regulate the supply voltage when the supply voltage is first powered up. The regulated supply voltage is doubled to a voltage level sufficient to activate the integrated analog circuit's bandgap voltage. The activated bandgap voltage is thus switched on to supply a more precise reference voltage to the regulator so that the diode-connected transistor may be de-activated to conserve power. The circuit also provides a bypass path for connecting the supply voltage directly to the integrated analog circuit when the supply voltage is the same level as the necessary voltage for the integrated analog circuit.

Abstract: A digitally driven, analog bandpass filter has an analog summer and two analog delay elements connected in a loop. An input signal to the filter is applied to a plus input terminal of the summer, and the output of the second delay elements is applied to a minus input terminal of the summer. The output of filter may be taken either from the output of the summer, or from the output of the second delay element, or from any point in between. Each delay element is driven by a two phase non-overlapping clock, and each element passes a charge from a first capacitor through an op amp to either a second capacitor (first phase) or a third capacitor (second phase). Amplification may be provided by adjusting the ratio of the second (or third) capacitor to the first capacitor. If a differential op amp is used, both sides of the op amp are clocked together, and each side has its own trio of capacitors identical to the trio on the other side.

Abstract: A novel supply discriminator circuit is disclosed for detecting the level of a supply voltage during power-up of a system for configuring an integrated analog circuit such as a PCMCIA card. The circuit compares a reference voltage with a divided down supply voltage and latches the result a predetermined delay later. The delay thus provides timing for the supply voltage to stabilize after power-up to assure accurate detection, as well as noise immunity from other devices.

Abstract: A circuit for detecting a system reset caused by the turning on of power supply of an electronic system. The circuit comprises: latch means coupled to said power supply having a SET input and an output, said output of said latch means being reset to a first predetermined state during power-on; feedback means for receiving said output from said latch means and said system reset, said feedback means activating its output when both of said first predetermined state from said latch means' output and said system reset are present; delay means coupled to the output from said feedback means and to said latch means, said delay means activating its output a predetermined time after said delay means receiving an activated output from said feedback means, said activated output from said delay means setting said latch means to a second predetermined state such that said feedback means remains de-activated when only said system reset is present without power-on.

Abstract: An apparatus and method is provided for detecting and amplifying the level of a received signal in the analog front end of a modem so as to maintain the level of the signal below a predetermined signal clipping level. An incoming signal is amplified by a predetermined amount of gain to provide a received signal. The level of the received signal is compared to a first reference level and a second reference level by a signal level detector. The comparative information regarding the level of the received signal is provided to a signal adjustment controller which provides control signals to the amplifier to maintain the received signal level between the first and second reference levels.

Abstract: A modem is adapted to accommodate a call waiting feature so that a user can select to continue an ongoing call or accept an incoming call. The modem detects a call waiting signal and generates a call waiting message. Where a call waiting signal is preceded by a loss of carrier, the modem detects the loss of carrier and then detects the presence of energy in a call progress band indicating that a new call is waiting. The modem can be selectably programmed to process the call waiting signal or to provide a call waiting message to a communications software package that can process the call waiting signal. The modem, in conjunction with the communications of software package, responds to the call waiting signal by asking whether the user wants to answer the incoming call or continue with the ongoing communication. The modem generates a programmable default response if the user does not respond within a prescribed time.