A system and a method for generating an error voltage

Abstract

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 currentwhose 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.

Description

technical field [0001] The present invention relates to the field of switched capacitor circuits and techniques and more particularly to the use of such circuits in the implementation of precision current generators and precision oscillators. Background technique [0002] Switched capacitor networks are widely used in the design of electronic circuits due to their ability to simulate resistive loads in circuits. Using a switched capacitor Csw switched at a frequency fsw, an equivalent resistance Req can be realized with Req=1 / (fsw×Csw). It is known that in the manufacture of semiconductor integrated circuits, the absolute accuracy of the resistance value is not easy to achieve, but the absolute accuracy of the capacitance value is just under the control of most semiconductor manufacturing processes. For this reason, the use of switched capacitor circuits in analog semiconductor circuit design is particularly important where precise resistance values ​​are required. [0003...

AI Technical Summary

Problems solved by technology

However, this simple solution consumes a large chip area if the circuit is to be integrated on a semiconductor chip

Additionally, the pole induced at node (NB) will be shifted to a lower frequency, conflicting with the main dominant pole of the regulation loop and making it difficult to achieve loop stability

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