Patent ID: 7477098
Filing Date: 2009-01-13
Classification: H03H

Abstract:
1. A tuning circuit in a system providing a clock signal for tuning an active filter corresponding to a target count value indicative of a predetermined RC time constant of the active filter, the tuning circuit comprising: a resistor-capacitor circuit comprising a variable capacitor, a first resistor, and a second resistor serially connected to the first resistor; a voltage generator for providing a first constant reference voltage to the first resistor, the first constant reference voltage being convened to a second constant reference voltage through the second resistor; a current replicating unit for replicating a first current into a second current with a current replication ratio, the first current being flowing through the first and the second resistors, and the second current being flowing through the variable capacitor; a comparator for comparing a charging voltage across the variable capacitor with the second constant reference voltage when the second current is charging the variable capacitor; a counter coupled to the comparator, for counting a number of cycles of the clock signal until the charging voltage reaches the second constant reference voltage; and an adjustment unit coupled to the counter, for calibrating a capacitance of the variable capacitor based on the number of cycles of the clock signal and the target count value.