National Semiconductor Corporation

Rudolphe Gustave Hubertus Eschauzier

Bram Nauta

Willem J Kindt

Nico Van Rijn

Eric Antonius Maria Klumperink

Marc Gerardus Maria Stegers

Arie J Van Rhijn

Wouter Groothedde

A dual-output current driver includes a pair of output stages that provide output current to various devices such as LEDs and laser diodes. An output-stage selector circuit that includes a differential pair is arranged to activate one of the output stages at a time. A pair of push-pull circuits may be employed to drive the differential pair such that high speed switching is possible. A single-ended to differential conversion circuit controls the push-pull circuits. The selected output stage receives a drive current from a differential pair circuit in a current driver circuit. The current driver circuit includes another pair of push-pull circuits that drive its differential pair circuit, and one or more additional differential circuits that are arranged to activate the push-pull circuits. The various differential pair circuits in the current driver circuit can be arranged to provide phase reversal, or modulation of the drive current in the output stages.

Dual-output current driver

A two-wire interface for a digital microphone circuit includes a power line and a ground line. The interface utilizes the ground line as a 'voltage active line' to transmit both clock and data signals between the digital microphone circuit and a receiving circuit. The digital microphone circuit detects the clock signal on the voltage active line and uses the detected clock signal to operate an ADC to provide digital data. The digital data is used to selectively drive current back to the receiving circuit over the voltage active line. The receiving circuit detects the transmitted data by monitoring the voltage associated with a line termination. The impedance associated with the line termination is switched by the receiver circuit to modulate the clock signal on the voltage active line.

Two-wire interface for digital microphones

A method and apparatus are provided for adjusting an offset in an electronic circuit by shifting at least one threshold voltage of a MOS transistor in an electronic circuit. By biasing a transistor into hard saturation, with sufficient supply voltage, charge carriers will be injected into the oxide layer of the MOS transistor over a predetermined time interval. Injection of charge carriers into the oxide layer of a MOS transistor causes the absolute value of the MOS transistor threshold voltage to increase. The injection of charge carriers is used to either intentionally increase or decrease the offset voltage in an electronic circuit due to mismatched components, process variations or to improve overall system accuracy or performance. In an operational amplifier or comparator, systematic offset voltage is measured at the output of the amplifier, and the threshold voltages of the differential input stage transistors are adjusted accordingly. In a digital to analog converter using precision current sources, the output voltage is measured for various code bits and the current levels for each current source are adjusted by shifting the threshold voltages as required. Offset voltage or mismatches in currents may be shifted in packaged electronic parts. The hot carrier injection method and apparatus, does not alter the temperature coefficient of the electronic part, requires minimal additional circuitry in electronic circuits, and greatly improves the precision with which electronic circuits may be manufactured.

Offset trim using hot-electron induced VT-shifts

The invention includes a differential input stage that is coupled to a turn around stage with a differential output. The input common mode voltage range is independent of the output common mode voltage range and the electronic circuitry is suited for use with other circuits such as an amplifier. The circuitry provides Class AB operation with quiescent and bias currents that are significantly less than the maximum output signal current so that overall power consumption is significantly reduced. The biasing of the output transistors in the turn around stage is floated and the invention is well suited for use with other circuits that require an input stage that can operate between the rails of a voltage supply. Also, the amount of noise is reduced and the offset performance of the circuit is improved by cross coupling the emitters of separate transistors employed to bias the output transistors in the turn around stage. Additionally, a complementary input stage can receive a differential input signal with a common mode voltage that is at, or between, the rails of the voltage supply. Further, a pair of turn around stages are adapted to combine the currents outputted by the complementary input stage.

Apparatus and method for a turn around stage having reduced power consumption, Class AB behavior, low noise and low offset

An electronic circuit for a Class AB output stage that has a differential input and a single ended output. A pair of clamp transistors are coupled between the bases of a pair of output transistors so that cross-over distortion is reduced and the output transistors do not completely turn off. A floating current source is employed to provide a stable quiescent current over a range of supply voltages. Also, the types and sizes of the transistors in the floating current source and the clamp transistors are matched so that any non-linear change in the operation of the clamp transistors caused by the Early effect over a range of supply voltages is automatically compensated for.

Growing community of inventors

Bergschenhoek, Netherlands

Rudolphe Gustave Hubertus Eschauzier