| 摘要 |
<p>The invention allows for the realization of a precision current reference or a fully integrated crystal-less precision oscillator by providing a circuit that precisely controls the cyclic charging operation of a switched capacitor. The voltage across the switched capacitor is ramped up and stops at the end of the charge phase at precisely a desired voltage. By using an appropriate network of switches based around a transconductance amplifier, the error voltage between the desired voltage and the voltage across the switched capacitor is amplified by the transconductance amplifier to give an error current. The error current is integrated over time to give an integrated amplified error voltage. By using appropriate feedback, the error voltage can be minimised to give a precise output current whose value depends on a capacitance, a voltage and a frequency. In a different feedback configuration the circuit described can be used as part of a frequency locked loop to provide a precise crystal-less oscillator whose frequency depends on a resistance and a capacitance. The circuit is insensitive to amplifier offset and bandwidth, switch resistance, duty cycle and non-symmetrical ripple at the input of the amplifier. The circuit also comprises means to compensate for temperature variations and means to compensate for variations in resistance and capacitance commonly occurring in integrated circuits due to process variations.</p> |
