Stmicroelectronics S.r.l.

Sgs-thomson Microelectronics S.r.l.

Claudio Tavazzani

Giorgio Ghiozzi

Marco Masini

Edoardo Botti

Fabrizio Stefani

Giorgio Chiozzi

Sandro Storti

Andrea Fassina

Stefania Boiocchi

An integrated power operational amplifier can alternatively be operated in a master or a slave mode, such that a master amplifier can be connected in parallel with one or more slave amplifiers. This arrangement allows very low impedance loads to be driven, as well as allowing the heat dissipation to be distributed over a number of operational amplifiers, thereby raising the maximum dissipation limits of integrated power systems. In addition, by eliminating the ballast resistors, more power can be delivered by the system, for the same supply voltage, and less power is dissipated.

Integrated power amplifier which allows parallel connections

A constant limit duty-cycle is established by detecting the equivalent values VDD&prime; and &minus;VDD&Prime; of the voltages to which the output signal of the amplifier switches or pseudo supplies. An input limiting stage receiving an analog input signal utilizes the pseudo supply values VDD&prime; and &minus;VDD&Prime; as respective reference values for limiting the voltage swing of the analog signal output to a pre-defined fraction &agr;<1 of such reference values. This avoids using as a reference the real supply voltage values VDD and &minus;VDD, as commonly done. The constant limit duty cycle is substantially independent from fabrication process spreads, temperature, etc., and provides an optimal functioning of the final stage of the amplifier for all working conditions.

Constant duty-cycle limiting of analog input signal swing in a class-D amplifier

An integrated power operational amplifier can alternatively be operated in a master or a slave mode, such that a master amplifier can be connected in parallel with one or more slave amplifiers. This arrangement allows very low impedance loads to be driven, as well as allowing the heat dissipation to be distributed over a number of operational amplifiers, thereby raising the maximum dissipation limits of integrated power systems. In addition by eliminating the ballast resistors, more power can be delivered by the system, for the same supply voltage, and less power is dissipated.

A power stage for an operational amplifier includes an output stage, a current source stage, and a gain stage. The output stage is formed by first and second NPN output transistors arranged in a Totem-Pole configuration, each having respective resistors connected between their respective base and emitter terminals. The output transistors are biased in class AB by a quiescent current supplied by the current source stage and are controlled dynamically by the gain stage. The gain stage includes an NPN gain transistor having a collector terminal connected to the base terminal of the first output transistor and an emitter terminal connected to the base terminal of the second output transistor.

Power stage, particularly for an operational amplifier

An amplifier is formed by an astable multivibrator having a signal output supplying a two-state output signal to a power stage, that presents an output voltage (V.sub.o) switching between a first and second value. The output voltage presents a duty cycle varying with the input signal (V.sub.in) of the multivibrator. The amplifier, when connected between first and second supply lines that are symmetrical with respect to ground and are subject to supply noise, comprises a current source for generating the bias current of the astable multivibrator and supplying a current (I) that is switchable at each half cycle. The value of the current at each half cycle is proportional to the absolute value of the output voltage (V.sub.o) of the amplifier to vary the duty cycle of the amplifier in a manner correlated the supply noise, so that the average output voltage value is zero.

Single-output dual-supply class D amplifier

Circuit for protection of an amplifier stage comprising circuit switching means for turn-off of the stage and piloted through a logic gate OR by a monostable, which generates upon arise of abnormal operating conditions turn-off command signals having a predetermined duration. A sensing circuit upon persistence of abnormal conditions at start-up or during normal operation also sends turn-off signals through the logic gate OR after enablement through a gate AND. The signals of any enablement at the logic gate AND arrive through a logic gate OR from a window comparator coupled with stage start-up members, from the monostable, and from the output of said logic gate AND as a confirmation signal.

Apparatus and method for protecting an amplifier circuit

An amplifier comprising a power stage the output of which is compared with a reference level by a comparator. If the output exceeds the reference level, a reduction is made in the gain of a variable-gain cell upstream from the power stage. The reference level varies with temperature, and, more specifically, presents a high constant value (e.g., greater than the supply voltage) when temperature is below a predetermined threshold (e.g., 130.degree. C.), and decreases in proportion to an increase in temperature, when the temperature exceeds the predetermined threshold. Thus, the input signal is only attenuated in the event the output signal exceeds given values inversely proportional to temperature, and with no reduction in peak output at high temperature.

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Trivolzio, Italy

Claudio Tavazzani