is a circuit arrangement for the above mentioned comparator 22 25 26 are npn transistors 21 23 24 28 are resistances and 27 is a capacitor the output terminal a of the above mentioned comparison wave circuit is connected with the base of the transistor 22 both emitters of the transistors 22 25 are connected together and at a same time these emitters are connected to the collector of the transistor 26 forming a differential type amplification circuit the part 7 distinguished by the two dot broken line is a circuit arrangement for the above mentioned differential amplifier 42 43 44 48 49 are resistances and 45 46 47 are npn transistors the base of the transistor 45 is connected with the generation circuit of a reference voltage source 8 which is to be described later and its collector is connected with the base of the transistor 25 of the above mentioned comparator 5 through the resistance 34 the emitters of the transistors 45 46 are connected to each other and at a same time they are connected with the collector of the transistor 47 the transistor 47 and the resistance 49 form so called constant current circuit this differential amplifier 7 can be composed as an ic unit which can provide space wise advantage the part 8 distinguished by the two dot broken line shows a generation circuit for the above mentioned reference voltage source 8 36 is a resistance and 37 to 40 are diodes for temperature compensation of the reference voltage source 8 f.