Comparator Circuit and Method for Operating a Comparator Circuit

Abstract

A comparator circuit for comparing a first voltage signal to a second voltage signal is described. The comparator circuit includes a first comparator and a second comparator and a selection unit for selecting one of the comparators depending on a selection condition. The invention also provides a method for operating a comparator circuit.

Description

CLAIM OF PRIORITY [0001] This application claims priority to Application No. 06117795.2 filed Jul. 25, 2006, the entire content of which is incorporated by reference herein. BACKGROUND OF THE INVENTION [0002] The invention relates to a comparator circuit and a method for operating a comparator circuit according to the preambles of the independent claims. [0003] Successive approximation analog-to-digital converters (ADC) are well known in the art. Such ADCs use a comparator to reject ranges of voltages, eventually settling on a final voltage range, and convert one bit per cycle. A typical successive approximation ADC comprises a reference voltage generator, a comparator and a successive approximation register. A general description of this kind of ADCs can be found for example in Allen / Holberg: “CMOS Analog Circuit Design”, Oxford University Press 2002, 668-672. [0004] A single-rail comparator supports a limited input voltage range only. Normally asymmetric input range, starting at s...

AI Technical Summary

Benefits of technology

This solution enables high accuracy and extended input voltage range, reducing process and temperature dependencies, and allows for self-calibration, thereby enhancing the resolution and reliability of measurements in applications like thermal and supply voltage sensing.

Problems solved by technology

Additionally, the overall power consumption is low, especially compared to so called flash analog-to-digital converters.

It is known that offset-errors and gain-errors affect the comparator accuracy.

Additionally, the comparator gain is a function of the common mode input voltage which results in limiting the useable input voltage and, further, an available input voltage swing is limited by the input buffer / sample-and-hold circuit, which is usually used at the comparator input.

But as already mentioned above, the comparator is one of the main sources of inaccuracy in such a circuitry.

Very low or very high input voltages close to the power supply rail voltages show a very low gain and yield high inaccuracy.

However, a rail-to-rail comparator or operational amplifier design introduces additional offset and error sources.

Full rail-to-rail operation can still not be achieved.

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