Abstract: A circuit is provided to detect which of a simultaneous plurality of varying input signals has the dominant maximum amplitude. Two simultaneous input signals are compared with each other; or each of more than two simultaneous input signals is compared individually with a common, varying, comparing signal, provided in response to the summing of the input signals, and the subsequent scaling of the summation. The input signals, and a provided comparing signal, are different from each other, only, in amplitude. Normally there is expected, at least in relation to the input signal having the dominant maximum amplitude, to be a wide dynamic extent of amplitudes; whereas each signal supplied to a difference amplifier for such a comparison is arranged to have only a low amplitude, at least the dominant input signal being supplied so as to have only a range of amplitudes, as transmitted by an associated limiting amplifier in response to the receipt of the signal.

Abstract: A laser energy control circuit for a gas-discharge excited laser includes an energy source PSU to supply energy to the gas discharge. First circuit means TR1, TR2 operate to limit the energy supplied to a first value for a first time interval, after which second circuit means A1, A2 allow the energy to rise to a maximum value and then decrease gradually to a second value over a second time interval. Subsequently, third circuit means including amplifiers A3 to A6 operate to maintain the light output of the laser at a desired value.