Two stage analoge-to-digital converter having unique fine encoding circuitry

An analog-to-digital converter for the conversion in two steps of a sampled analog input signal voltage to an output digital code, having x bits, wherein x is the number of bits in said output digital code, that represents a magnitude of said analog input signal voltage, comprising:

• a) an input sampling means that will capture and retain the sampled analog input signal voltage instantaneously at interval periods from an analog input signal voltage during a first half cycle;
• b) a coarse analog-to-digital converter having a first plurality of comparator circuits to compare the sampled analog inputs signal voltage to a plurality of coarse reference voltages to create coarse digital thermometer code representing a coarse estimation of the magnitude of said sampled analog input signal voltage during a beginning period of a second half cycle;
• c) a fine analog-to-digital converter having a second plurality of comparator circuits to compare the sampled analog input signal voltage to a portion of a plurality of fine reference voltages to create a fine digital thermometer code that represents a refinement of the coarse estimation of said sampled analog input signal voltage during an ending period of the second half cycle;
• d) A voltage reference generator connected between a first reference voltage source and second voltage reference source, comprising a plurality of serially connected resistors that form a voltage divider network, wherein a voltage developed at the juncture of tow of the serially connected resistors is one of the voltages of the plurality of coarse reference voltages and the plurality of fine reference voltages;
• e) a voltage reference selection switch network to couple a selected portion of the plurality of fine reference voltages to the fine analog-to-digital converter, comprising a plurality of switched, wherein each switch is connected to the juncture of two of the plurality of serially connected resistors and will selectively couple one of the fine reference voltages to one of the comparators of the fine analog-to-digital converter;
• f) a voltage reference selection switch logic means to activate a selected portion of the voltage reference selection switch network as determined by the coarse digital thermometer code;
• g) a coarse analog-to-digital converter encoder to translate the coarse digital thermometer code to a most significant portion of the output digital code;
• h) a fine analog-to-digital converter encoder to translate the fine digital thermometer code to a least significant portion of the output digital code, comprising
• a thermometer code interpreter array having a plurality of thermometer code inputs connected to the fine digital thermometer codes, an array of logical decision means to determine a boundary bit between the first logical state and the second logical state of the fine digital thermometer code, and an interpreter output to transfer the boundary bit;
• and
• a read only memory containing all possible least significant portions of the output digital code, wherein the boundary bit and an even or odd column selection bit selects an appropriate least significant portion of the output digital code.
• i) an output code correction means to adjust the most significant portion of the output digital code to correct any error created in the coarse comparison means and transfer and adjusted output digital code to circuitry external to said two step analog-to-digital converter.