Description on high threshold logic gate

i want the description for high threshold logic.ifpossible can anyone suggest me site where I cud gt detailed explaination..or the reference book...

High threshold logic circuits are used in place of a diode driven logic where voltage noise may cause it to produce an unwanted output. Below 1 volt is a logical zero and above 3 volts is a logical one. For more info, you might want to do a search for "Zenier Diode." They are often used in high threshold logic circuits.