US 8,552,797 B2 · High accuracy RC calibradion circuit

Abstract

In an RC calibration circuit, a single reference current is used to generate voltages across both a resistive and capacitive element. The component value of one of the resistive and capacitive element is successively altered until the voltages are substantially equal. Additionally, parasitic capacitances in the circuit are precharged to the resistive element voltage prior to the comparison. The RC calibration circuit eliminates the errors due to current matching and parasitic capacitances in prior art calibration circuits. The circuit includes a comparator and a digital control circuit (DCW) including a successive approximation register (SAR) holding the value of the digital control word used to control the component value of the tunable resistive or capacitive element. The SAR alters the DCW in an iterative, bit-by-bit binary searching pattern in response to the comparator output.

Claims19

Dependent claims

An RC calibration circuit, comprising:

a resistive element;
a capacitive element;
wherein at least one of the resistive and capacitive elements is tunable;
a current source providing a single reference current;
a switching element interposed between the current source and the resistive and capacitive elements, and operative to selectively direct the single reference current through one of the resistive and capacitive elements at a time;
a comparator operative to determine a voltage difference by comparing voltage drops across the resistive and capacitive elements;
and
a control circuit operative to control the switching element to direct the single reference current through the capacitive element for a predetermined duration to charge the capacitive element, and to subsequently direct the single reference current through the resistive element, and further operative to tune at least one of the resistive and capacitive elements so as to minimize the voltage difference determined by the comparator.

5 more elements

Dependencies are inferred from the claim text.

High accuracy RC calibradion circuit

Life of this patent

High accuracy RC calibradion circuit

Life of this patent

Abstract

Claims19