| 摘要 |
<p>"Filter arrangement." A first resistor (R1) and a first capacitor (C1) constitute a filter arrangement having a time constant which is not very accurate due to the inaccuracy of the resistor and the capacitor values in intergrated circuits. The time constant is adjusted using a circuit comprising a reference resistor (R2) and a switched capacitor (C3). The value of the reference resistor (R2) and the equivalent resistance of the switched capacitor (C3) are compared by means of an integrator (C2, 2) from whose output (9) a control voltage is taken via a hold circuit (C4, C5), which control voltage is equal to the voltage at that point on the reference resistor where the resistance value is equal to that of the switched capacitor (C3). By means of comparator (21 to 30) and switches (S11 to S20) a percentage of the total resistance of the first resistor (R1) is short-circuited, which percentage is equal to the difference between the resistance of the reference resistor (R2) and the equivalent resistance of the switched capacitor (C3), expressed as a percentage of this equivalent resistance. (Fig. 1).</p> |
