At&t Bell Laboratories

Agere Systems Inc.

Roger L Minear

Scott H Early

Parag Parikh

Richard Booth

A signal generator circuit includes a controller adapted to generate a divide value in accordance with at least a first control signal, and a divider adapted to divide an output signal of the signal generator circuit by the divisor value. The controller is selectively operable in at least one of a plurality of modes in accordance with at least a second control signal. The controller is configured to calculate each of one or more new divide values so as to vary a frequency of the output signal in accordance with at least one of the first and second control signals. The controller is configured to switch between operational modes and/or switch between divide values, the switching between operational modes and/or divide values being performed in such a manner so as to substantially eliminate discontinuities in the frequency of the output signal.

Signal generator with selectable mode control

An integrated circuit amplifier for a high impedance microphone (100) of the capacitance type is disclosed. The subject amplifier circuit permits the further miniaturization of an electret microphone as it is capable of providing an input impedance simulating a resistor value of hundreds of megohms. The circuit particularly comprises duplicate coupling circuits (101a and 101b), a source of reference direct current voltage (103), and a gain providing circuit (102). The coupling circuits (101a and 101b) comprise a first pair of diodes (Q1 and Q2) symmetrically placed about one input terminal (IN1) of the microphone (100). Outputs of the reference voltage source (103) are provided to coupling circuits (101a and 101b) and through the coupling circuits to gain providing circuit 102. Such an arrangement facilitates power supply noise rejection and automatic canceling of direct current voltage drifts.

High input impedance circuit

An integrated circuit amplifier for a high impedance microphone (100) of the capacitance type is disclosed. The subject amplifier circuit permits the further miniaturization of an electret microphone as it is capable of providing an input impedance simulating a resistor value of hundreds of megohms. The circuit particularly comprises duplicate coupling circuits (101a and 101b), a source of reference direct current voltage (103), and a gain providing circuit (102). The coupling circuits (101a and 101b) comprise a first pair of diodes (Q1 and Q2) symetrically placed about one input terminal (IN1) of the microphone (100). Outputs of the reference voltage source (103) are provided to coupling circuits (101a and 101b) and through the coupling circuits to gain providing circuit 102. Such an arrangement facilitates power supply noise rejection and automatic canceling of direct current voltage drifts. A current repeater circuit (FIG. 8) is employed generally throughout the integrated circuit amplifier for driving various elements. The current repeater comprises at least one unipolar transistor to permit operation at low direct current voltages, while providing an accurately controlled current transfer ratio.

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Wyomissing, PA, United States of America

Roger L Minear