| 摘要 |
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.
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