Introduction

Abstract

In this era where the market for portable electronic systems such as wireless communication devices, hearing aids, consumer electronics, etc. is continuously expanding, there is a growing need for the development of low voltage and low power circuit techniques and system building blocks. Both low voltage operation and low power operation are of great importance for portable applications. Low voltage operation is demanded because it is desirable to use as few batteries as possible for size and weight considerations. Low power consumption is necessary to ensure a reasonable battery lifetime. An example of a standard system building block is an Analog to Digital Converter (ADC), unavoidable as interface between the analog world and the digital signal processing hardware. A very widespread type of ADC in telecommunications applications or audio and voice applications is the ∆Σ modulator. A ∆Σ modulator is suited for low to medium speed but high resolution conversion. Other types of converters exist. Successive approximation and algorithmic converters can perform medium speed and medium accuracy conversion. Examples of high speed but low to medium accuracy converters are flash, interpolating, folding and pipelined converters. Compared to the last two classes of converters whose performance is ultimately limited by matching properties, the ∆Σ ADC has the advantage of being quite insensitive to circuit imperfections such as device mismatch and non-ideal opamp behavior. When designing for very low voltage and low power operation, the latter advantage becomes even more important. The lower the supply voltage, the more difficult it is to maintain specifications such as high gain, to mention just one.