Method and device for determining the ratio between an RC time constant in an integrated circuit and a set value

A device for determining a ratio of an actual value of an RC time constant of an RC network in an integrated circuit to a desired value of the RC time constant of the RC network, comprising:

• a first reference RC network having a first resistor and a first capacitor and a second reference RC network having a second resistor and a second capacitor, the first and second RC networks being oppositely connected between first and second supply potentials, a product of a resistance value of the first resistor and a capacitance value of the first capacitor being equal to a product of a resistance value of the second resistor and a capacitance value of the second capacitor;
• a comparator having a first input connected to a first node common to the first resistor and the first capacitor and having a second input connected to a second node common to the second resistor and the second capacitor;
• a counter having a count which is changed by an output signal from the comparator as clocked within an evaluation period;
• first and second discharge circuits connected to the first and second capacitors respectively and which discharge the first and second capacitors respectively depending on the comparator output signal;
• and
• means for the determining a quotient that represents a ratio between a normalized RC time constant of the first and second reference RC networks and an actual RC time constant of the first and second reference RC networks.

A device for determining a ratio of an actual value of an RC time constant to a desired value of the RC time constant, the ratio being indicative of an amount by which the actual value of the RC time constant deviates from the desired value of the RC time constant, comprising:

• a first reference RC network having a resistor and a capacitor and a second reference RC network having a resistor and a capacitor, the first and second reference RC networks having an RC time constant with a value that depends on values of the resistors and the capacitors of the first and second reference RC networks;
• a comparator having a first input connected to a node of the first reference RC network and having a second input connected to a node of the second reference RC network, the comparator comparing the potentials at the nodes and providing an output signal indicative thereof;
• a timing circuit that controls the charging and discharging of the capacitors of the first and second reference RC networks in response to the comparator output signal;
• a counter having a count controlled by the comparator output signal, where the counter counts during a predetermined evaluation period of time;
• a first charge and discharge circuit connected to the capacitor of the first reference RC network that charges and discharges the capacitor of the first reference RC network during the predetermined evaluation period of time;
• a second charge and discharge circuit connected to the capacitor of the second reference RC network that charges and discharges the capacitor of the second reference RC network during the predetermined evaluation period of time;
• where a predetermined number of the charges and discharges of the capacitors of the first and second reference RC networks depends on a length of the predetermined evaluation period of time;
• and
• where the counter counts an actual number of the charges and discharges of the capacitors of the first and second reference RC networks that occur during the predetermined evaluation period of time, a quotient of the predetermined number of the charges and discharges and the actual number of the charges and discharges representing a ratio between the desired value and the actual value of the RC time constant of the first and second reference RC networks.