IC Clamping circuit

In an integrated circuit of the type having first and second supply terminals and functional circuitry with input control terminals which are either connected to supply potential to activate said functional circuitry to operate in a first mode or are caused to remain unconnected to enable said functional circuitry to operate in a second mode, an improved means for clamping the potential of said input terminal to potential at the first supply terminal with said input control terminal in the unconnected condition comprises:

• a transistor having first and second electrodes and a principal conduction path therebetween, a control electrode, potential between the control and first electrode controlling the conduction path;
• first and second means connecting the first and second electrodes of the transistor to the first supply and input control terminals respectively;
• a two input NAND circuit having a first input connected to the input control terminal, an output connection connected to the control electrode of the transistor and having a second input connection;
• the NAND circuit being arranged to provide a first output potential sufficient to condition the transistor to conduct for either or both of its input connections exhibiting a potential more nearly equal to the potential applied to the first supply terminal than the potential applied to the second supply terminal and said NAND circuit providing an output potential sufficient to maintain the transistor cut off otherwise;
• an INVERTER circuit having an input terminal connected to the output connection of the NAND circuit and having an output connection at which signals are available for controlling the functional circuitry, said signals being the same logical sense as the potential at the input control terminal;
• initialization means for generating a first potential more nearly equal to the first supply potential than the second supply potential for a prescribed duration, subsequent to first and second supply potentials being applied to the first and second terminals, and a second potential being more nearly equal to the second supply potential than the first supply potential thereafter, as long as the first and second supply potentials are continuously applied;
• and
• means for applying the potentials generated by the initialization means to the second input of said NAND circuit.

In combination, a circuit having a control terminal, said control terminal establishing one of a first and second modes of operation of a functional circuit in accordance with one of a first and second supply potentials applied thereto and wherein said control terminal is liable to remain unconnected to establish the other of the first and second modes of operation, further circuitry comprising:

• a transistor having first and second electrodes and a principal conduction path therebetween, a control electrode;
• potential between the control and first electrodes controlling said conduction path;
• means connecting the second electrode of the transistor to the control terminal;
• means for connecting the control terminal to one of said first and second supply potentials to establish the mode of operation;
• means connecting the first electrode of the transistor to the other of said first and second supply potential to which the control terminal is connected;
• control circuitry having an output terminal connected at the control electrode of said transistor, for generating a potential to condition said transistor to conduct responsive to the potential at said control terminal and conditioning said transistor to conduct momentarily subsequent to applying supply potentials to the circuitry.