Amplifiers – With semiconductor amplifying device – Including differential amplifier
Reexamination Certificate
2002-12-30
2004-10-05
Shingleton, Michael B (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including differential amplifier
C330S260000, C330S265000, C330S098000, C330S099000, C330S100000
Reexamination Certificate
active
06801087
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an integrated circuit with an output stage that includes an analog amplifier connected, on the output side, to a terminal pad for the outputting of an amplified output signal.
In integrated circuits with analog signal processing, operational amplifiers or operational transconductance amplifiers (OTA), for example, are provided for outputting output signals to lines external to the circuit. As a result, the output signal is output with high driver power from the integrated circuit to a line on a circuit board. In conventional operational amplifiers or OTAs as presented for example in Tietze, Schenk: “Halbleiterschaltungstechnik”, [“Semiconductor Circuitry”], 9th Edition, 1991, page 140; Hogervorst, Huijsing: “Design of Low-Voltage, Low-Power Operational Amplifier Cells”, pages 150 and 188; Laker, Sansen: “Design of Analog Integrated Circuits and Systems”, page 487, a capacitive feedback path is connected to the output terminal. The amplifiers are connected up with feedback networks, each individual amplifier stage effecting a phase shift in the signal path. To avoid positive feedback signal components, high frequency components are attenuated by the capacitive feedback mentioned.
A bonding wire is usually connected to the terminal pad for the outputting of the output signal from the integrated circuit, the bonding wire connecting the terminal pad to a terminal pin of the housing. This configuration acts as a receiving antenna for high-frequency interference radiations that can be generated by adjacent circuit components, for example. The signal path that is formed by the capacitive feedback but has low resistance for high frequencies leads from the terminal pad back into the circuit. The high-frequency interference radiation, so-called electromagnetic compatibility (EMC) interference, which is substantially received by the bonding wire is rectified by the pn junctions present in the integrated circuit. The currents injected as a result shift the operating points of the circuits in the integrated circuit. Inputs of amplifier stages are usually embodied with high resistance. As a result, currents so injected noticeably interfere with the signal processing.
The reference De Bruyn, William: “Error feedback in audio power”, Electronics World, June 1997, pages 476 to 478, in particular,
FIG. 1
therein, shows an analog amplifier with a first amplifier stage, containing a differential amplifier, and also an output stage, in the case of which the output is fed back through resistive and capacitive elements to the output of the differential amplifier stage. The reference Tietze, Schenk: “Halbleiter-Schaltungstechnik” shows differential amplifiers with a first amplifier stage and a second amplifier stage connected downstream, in the case of which the output of the amplifier stage is fed back to the input, in particular, in the 9th Edition, 1990, pages 140 and 433, and the 11th Edition, 1999, page 523. The principle of amplifiers with nested Miller compensation is described in Pernici, Sergio et al.: “A CMOS Low-Distortion Fully Differential Power Amplifier with Double Nested Miller Compensation”, IEEE Journal of Solid-State Circuits, Volume 28, No. 7, July 1993, pages 758 to 763.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide an integrated circuit with an analog amplifier that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and that has an output-side analog amplifier with a higher strength with respect to electromagnetic coupling-in.
With the foregoing and other objects in view, there is provided, in accordance with the invention, an integrated circuit, including an input terminal for feeding in an input signal to be amplified, an output terminal for outputting an amplified output signal, a terminal pad connected to the output terminal for outputting the output signal, a terminal for a reference-ground potential, and an analog amplifier having a first input-side amplifier section having a first signal path and an output, a second output-side amplifier section having a second signal path, the first and second signal paths connected in series and a transistor having a control terminal coupled to the output of the first input-side amplifier section and a controlled current path coupled to the terminal for the reference-ground potential and to the output terminal, a series circuit having a resistor, a capacitive element, a node between the resistor and the capacitive element, and ends, one of the ends of the series circuit connected to the output terminal, and another of the ends of the series circuit connected to the control terminal, and a further capacitive element connected between the node and the terminal for the reference-ground potential.
According to the invention, the integrated circuit has an analog amplifier, which includes an input terminal for feeding in an input signal to be amplified and also an output terminal for outputting an amplified output signal, a terminal pad, which is connected to the output terminal of the analog amplifier and serves for the outputting of an output signal from the integrated circuit, the analog amplifier including a first input-side amplifier section and a second output-side amplifier section, whose signal paths are connected in series, and a series circuit including a resistor and a capacitive element, which is connected at one end to the output terminal of the analog amplifier, a node being formed between the resistor and the capacitive element of the series circuit, in which case the second amplifier section includes a transistor, whose control terminal is coupled to an output of the first amplifier section and whose controlled current path is coupled to a terminal for a reference-ground potential and to the output terminal of the analog amplifier, in which case the series circuit including the resistor and the capacitive element is connected at the other end to the control terminal of the transistor, and in which case a further capacitive element is provided, which is connected between the node and the terminal for the reference-ground potential.
In the case of the integrated circuit according to the invention, interference coupled in at high frequency through the output is attenuated. The capacitive element connected relative to reference-ground potential acts together with the resistor as a low-pass filter so that the coupled-in signal energy of the high-frequency interference is delayed and discharged to reference-ground potential. As a result, less charge is injected into the interior of the integrated circuit. Although low-frequency interference is, nevertheless, conducted further, it is detected by the control dynamic range of the analog amplifier and corrected.
The analog amplifier may be, for example, an operational amplifier that has a high-resistance input, effects analog amplification of the useful signal, and provides a low-resistance signal on the output side. By contrast, an OTA has a high-resistance output that supplies a current-controlled output signal. Operational amplifiers and OTAs are of multistage construction. A differential amplifier stage that operates differentially is provided on the input side, a further amplifier being connected downstream of the stage on the output side. The further amplifier substantially includes an amplifier transistor. The output of the analog amplifier and the input of this second amplifier stage exhibit capacitive feedback, which feedback includes the series circuit formed by a resistor and a capacitive element, the coupling node between capacitive element and resistor, in turn, being capacitively connected to reference-ground potential. The resistor is connected into the feedback loop between the output of the second amplifier stage and the input thereof. As an alternative, the resistor is connected between the output terminal of the analog amplifier, which is connected to the terminal pad, and the output terminal
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