JPS6488259A - Detecting device of amplitude level - Google Patents

Abstract

PURPOSE:To make it possible to judge immediately whether an amplitude level is within set limits or not, by a method wherein an alternating-current signal whose level is unknown is supplied to one input end while a voltage showing a positive peak within a set amplitude is impressed on the other input end. CONSTITUTION:When an input video signal (a) passes through a high-pass filter circuit 2, the reference level thereof is shifted so that areas on the positive and negative sides be equal. In the case when the positive-side peak level of the signal (a) is higher than an upper limit value VH of a set amplitude, an instantaneous input level VIN of the signal (a) is in the relationship with each of upper limit values VH and VL: VIN>VH and VIN>VL. Since VIN>VH, a first comparing amplifier 3 outputs a signal of high level. This signal has a horizontal period, and so an output (e) of a monostable multivibrator circuit 5 turns to be of high level. On the other side, an output (d) of a second comparing amplifier 4 is a signal of low level since VIN>VL, and so an output (f) of a monostable multivibrator circuit 6 turns to be of low level as well. Even when the level of the signal (e) from the circuit 5 turns to be high and low repeatedly, an output (g) of an AND circuit 7 shows a low level.