Abstract: An interface circuit to the output of a programmable voltage ramp generator for decreasing the minimum voltage step of such a generator having two voltage channels and a minimum voltage step greater than 1 millivolt. The interface circuit receives an input from each of the two voltage channels (V.sub.2, V.sub.3), along with an inserted voltage (V.sub.1). The circuit includes a summing amplifier for (i) compressing the minimum voltage step from one voltage channel (V.sub.2) by a factor equal to or greater than such minimum voltage step, (ii) adding the voltage from the other channel (V.sub.3) to the compressed voltage, and (iii) subtracting the inserted voltage (V.sub.1) (or adding an inserted voltage which is negative). The inserted voltage (V.sub.1) is equal in magnitude to the maximum output value from the voltage channel that has the voltage compressed (V.sub.2). The output of the summing amplifier (V.sub.out) may be represented by:V.sub.out =(V.sub.3 /X)+(V.sub.2 /Y)+(V.sub.

Abstract: Undoped GaAs single crystals with low dislocation density, low impurity content, 0.20-1 Kg in weight and constant diameter of 1"-2" (inches), said single crystals being obtained with LEC technology at low or high pressure with synthesis of the polycrystal in situ and subsequent growth of the single crystal.