Threshold switch

Abstract

To permit evaluation of only slowly changing low amplitude undulating signals, derived for example from a wheel-speed transducer of a brake anti-block system, and to obtain essentially square-wave output voltage signals having a 1:1 pulse to pulse gap ratio for further signal processing, a temperature stable threshold switch is provided by connecting transistors forming a difference amplifier and purposely mismatched to the input, the mismatch of the transistors defining the threshold level, and being obtained by mismatch in the output circuit thereof, preferably and for example by using pnp lateral transistors having multiple collectors in which the ratio of length of the partial collectors is other than 1:1, and connected, preferably, to a current mirror which has its output connected to the partial collector of the other of the pnp lateral transistors. The circuit can be further expanded by connection of the output to a flipflop to provide a true square-wave output, and may be made independent of input connection by providing input transistor circuitry, preferably in form of an emitter-follower. Rather than forming partial collectors of the lateral transistors of unequal ratio, the transistors forming the current mirror may be constructed to have different emitter surfaces; or both partial unequal collectors, or equivalents, and current mirror emitters or equivalents, can be used.