Programmable input range SAR ADC

Abstract

A programmable input voltage range analog-to-digital converter in which a split gate oxide process allows the use of high voltage (+-15 volt) switches on the same silicon substrate as standard sub-micron 5 volt CMOS devices. With this process, the analog input voltage can be sampled directly prior attenuation circuits. By only sampling on a given ratio of the sampling capacitors, the analog inputcan be scaled or attenuated to suit the dynamic range of the SAR (successive approximation register) ADC itself. In the system of the present invention, the sampling capacitor can be the actual capacitive redistribution digital-to-analog converter (CapDAC) used in the SAR ADC itself, or a separate capacitor array. By selecting which bits of the CapDAC or separate sampling array to sample on, one can program the input range. Once the analog input signal has been attenuated to match the allowed dynamic range of the SAR converter, traditional SAR techniques can be used to convert the input signal to a digital word.

Description

technical field [0001] The present invention relates generally to scaling of analog input signals, and in particular to scaling both bipolar and unipolar input signals to the dynamic range of an ADC prior to acquisition and conversion, and, more particularly, to converting analog input signals through high voltage transmission gates Sampled onto the selected combination of sampling capacitors to program the input range of the SAR ADC. Background technique [0002] Multiple-input, wide dynamic range bipolar and unipolar successive approximation analog-to-digital converters (ADCs) traditionally use a resistor divider network at the analog input to scale the input signal to the converter before acquisition and conversion can occur. dynamic range. This method of attenuating an input signal prior to conversion by an ADC has been used with great success in the past. However, it has many outstanding disadvantages. [0003] First, in the traditional resistor-divider approach, the...

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Problems solved by technology

Second, the resistor divider network draws power from both the internal reference and the analog input source

A third problem is that this prior art does not provide the user with an easy way to program the allowed range of analog inputs

A fourth disadvantage is the fact that the size of the input resistor will limit the full power bandwidth of the converter

However, if the user wishes to change the range, the hardware must be rewired

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