Abstract: A gain control system comprises a reference stage, a bias replication stage, an operational amplifier, an automatic gain control block, a gain stage, and a crystal oscillator in one embodiment. A negative feedback loop is formed by portions of the operational amplifier, the replica biasing stage, the gain stage, and the automatic gain control stage. The negative feedback loop operatively controls an amplitude of oscillation in the crystal oscillator. The automatic gain control block produces output currents at reference levels in proportion to an input current source. The output current reference levels provide a corresponding yet independent scaling of currents in the bias replication stage and the gain stage. By the scaling capabilities provided a high common mode of voltage is provided between the crystal oscillator and the voltage reference section while stable oscillating characteristics are provided over a broad frequency range.

Abstract: A rail-to-rail operational amplifier has a pair of input terminals and an output terminal, and includes first and second parallel-connected differential input stages configured to generate a differential output signal OUTN, OUTP in response to a differential input signal VINN, VINP received at the pair of input terminals. Each of the first and second differential input stages in turn includes a pair of source-follower transistors and a pair of bulk-driven transistors. The pair of source-follower transistors are respectively coupled between the pair of input terminals and a bulk terminal of the pair of bulk-driven input transistors. Further, the pair of source-follower transistors in the first differential input stage have a different threshold voltage than the source-follower transistors in the second differential input stage.

Abstract: A rail-to-rail operational amplifier has a pair of input terminals and an output terminal, and includes first and second parallel-connected differential input stages configured to generate a differential output signal OUTN, OUTP in response to a differential input signal VINN, VINP received at the pair of input terminals. Each of the first and second differential input stages in turn includes a pair of source-follower transistors and a pair of bulk-driven transistors. The pair of source-follower transistors are respectively coupled between the pair of input terminals and a bulk terminal of the pair of bulk-driven input transistors. Further, the pair of source-follower transistors in the first differential input stage have a different threshold voltage than the source-follower transistors in the second differential input stage.

Abstract: A gain control system comprises a reference stage, a bias replication stage, an operational amplifier, an automatic gain control block, a gain stage, and a crystal oscillator in one embodiment. A negative feedback loop is formed by portions of the operational amplifier, the replica biasing stage, the gain stage, and the automatic gain control stage. The negative feedback loop operatively controls an amplitude of oscillation in the crystal oscillator. The automatic gain control block produces output currents at reference levels in proportion to an input current source. The output current reference levels provide a corresponding yet independent scaling of currents in the bias replication stage and the gain stage. By the scaling capabilities provided a high common mode of voltage is provided between the crystal oscillator and the voltage reference section while stable oscillating characteristics are provided over a broad frequency range.

Abstract: Embodiments provide systems and methods for supporting reliable operation of crystals with widely varying fundamental modes of oscillation. In accordance with exemplary embodiments, an architecture is disclosed for an oscillator circuit which allows reliable operation for crystals varying over a wide frequency range, such as 12:1. Some embodiments use selectable current sources to provide variable range control for extending the range of frequencies over which the embodiments may operate properly. Other embodiments include symmetric topologies, cascode topologies, coupling elements, and/or other techniques to improve noise immunity and/or operation in low-source-voltage environments.