Abstract: There is disclosed a gain control amplifier wherein a signal input terminal (1) receiving an input signal (V.sub.in) is connected to a variable resistor portion (71) including an R-2R ladder resistor group and switches (K.sub.1 to K.sub.4), and an operational amplifier (10) and resistors (r.sub.1, r.sub.2, r.sub.3) construct an adding circuit (91), which outputs an output signal (V.sub.out) to a signal output terminal (5). Each of the switches (K.sub.1 to K.sub.4) includes terminals (A, B) and a common terminal (C) connected to one of the terminals (A, B). All of the terminals (A) arc connected to the signal input terminal (1) in common, and all of the terminals (B) are grounded in common. The ladder resistor group (R,2R) need not be of great resistance value. Thus, a gain control amplifier is achieved which is permitted to control a gain widely, finely and linearly without resistors of great resistance.

Abstract: A gain control amplifier is disclosed in which its gain changes continuously. Gain control amplifiers are connected in series between a signal input terminal and a signal output terminal. Each gain control amplifier is connected to an up-down counter via a D/A converter. A first up-down counter receives and counts gain control clocks, and increases the gain of a first gain control amplifier through a first D/A converter. When the up-down counter has registered a full count, the gain control clocks are input to a second up-down counter as a second output, during which the full count registered in the up-down counter is maintained as such. Thus, the gain of one gain control amplifier is increased only after the gain of the immediately preceding gain control amplifier has reached its maximum.

Abstract: Decarboxylation of carboxylic acids using diazabicycloalkenes and, if desired, also a simple copper salt, as the means for decarboxylation.