Abstract

An extension of the op-amp concept featuring two differential inputs is presented. In a closed-loop environment this circuit forces two floating voltages to the same value, and thus has many interesting applications in the analog circuit domain. The formal description of such a circuit, its nonidealities and restrictions are given. A monolithic integration of this differential difference amplifier (DDA) in a double-poly CMOS technology and the measured characteristics are described. Many applications of this circuit, including a voltage comparator with floating inputs, a voltage inverter without resistors and an instrumentation ampli #er with only two external gain determining resistors are discussed.

Citations