Sub-ranging analog-to-digital converter

An analog-to-digital converter comprising:

• a first flash converter for performing a first analog-to-digital conversion on an analog signal to determine a first plurality of bits of a multi-bit signal that is representative of the analog signal;
• means, responsive to information relating to said first plurality of bits of said multi-bit signal, for determining a range of values for said multi-bit signal, said range having a lower limit and an upper limit;
• and
• a second flash converter for performing a second analog-to-digital conversion on the analog signal to determine a second plurality of bits of said multi-bit signal that are less significant than said first plurality of bits, said second flash converter including a plurality of comparators with each of said plurality of comparators including a first input for receiving said lower limit, a second input for receiving said upper limit, a third input for receiving said analog signal, means for defining a threshold value within said range of values defined by said upper limit and said lower limit, and an output for providing a signal that is representative of the relationship of said analog signal to said threshold level.

A comparator for providing an output signal that is indicative of the relationship of an analog input signal to a threshold level that is in a defined range comprising:

• means for receiving an analog input signal, a first signal that represents an upper limit of a comparison range, and a second signal that represents a lower limit of said comparison range;
• means for defining a threshold level located between said upper limit and said lower limit of said comparison range;
• and
• means for processing said analog input signal, said first signal, said second signal and said threshold level to provide an output signal that is indicative of the relationship of said analog input signal to said threshold level said that is located between said upper limit and said lower limit of said comparison range, wherein said output signal has a first state when said analog input signal is greater than said threshold level and a second state that is different than said first state when said analog input signal is less than said threshold level.

A method for using a weighted digital-to-analog converter as a comparator comprising the steps of:

• providing a weighted digital-to-analog converter that includes a first input for receiving a first digital signal and a second input for receiving a second digital signal, a third input for receiving a reference signal, and an output for providing an analog signal that is representative of said first digital signal and said second digital signal;
• applying a first limit signal that defines an upper limit of a comparison range, rather than said first digital signal, to said first input;
• applying a second limit signal that defines a lower limit of a comparison range, rather than said second digital signal, to said second input;
• applying a first comparison signal, rather than said reference signal, to said third input;
• processing said first limit signal, said second limit signal, and said first comparison signal with said weighted digital-to-analog converter to produce a second comparison signal that represents a relationship between said first comparison signal and said range.