Pushbutton switch contact bounce suppression circuit - uses single non-inverting CMOS gate connected to its own input and in parallel with switch output blade

摘要

The switch is arranged so that the blade (6) selects between one of two possible inout circuits (4,5) and the contact fixed to the blade is connected to the output circuit. The blade (6) is also connected to the output of a CMOS gate which is connected to its own input. During switching the current in the output transistor of the gate is limited by the channel resistance which is several hundred ohms and only a little current is taken. When the blade (6) leaves one of the contacts (7) for the other contact (8), the input of the gate (14), and thus the input of the upstream circuit (3), are taken to a first logic state in which they are maintained by the feedback loop. This state is achieved irrespective of the prior position of the blade (6) during its movement of oscillation between the two contact points (7,8). Conversely, when the blade (6) leaves another contact point (8), the upstream circuit (3) enters a second logic state.