Level indicating circuit

A circuit for supplying to an indicator an indicating signal representing the magnitude of an input signal comprising:

• means for providing said input signal in the form of a pair of complementarily fluctuating signals;
• differential amplifier means receiving said complementarily fluctuating signals for providing a pair of amplified outputs representing said complementarily fluctuating signals, said differential amplifier means including a pair of transistors, each having a linear region of amplification for said input signal between cutoff and saturated regions, and means biasing said pair of transistors so that the sum of currents flowing through said transistors of said pair is at a constant level when said input signal is of a magnitude such that said transistors amplify in their linear regions but said sum of currents fluctuates when the magnitude of said input signal exceeds a predetermined threshold so as to drive one of said transistors to one of its cutoff and saturated regions;
• circuit means for supplying said indicating signal to said indicator;
• and
• detecting means connecting said differential amplifier means to said circuit means and detecting when said sum of currents fluctuates from such constant level so that said circuit means supplies said indicating signal only when the magnitude of said input signal exceeds said predetermined threshold.