Protective circuitry for a read only memory

Claim 1

In combination with a monolithic read only memory wherein, on start-up, elements must be biased before extant address signals are effective, the improvement comprising: (a) precharge circuitry connected to the output bit lines of the read only memory; and (b) actuating means for the precharge circuitry including monolithic circuitry for producing, when a biasing voltage is first applied and for a predetermined interval thereafter, a first signal at a logic zero level, means for inverting the first signal to a second signal at a logic one level, and logic circuits responsive to the second signal and to the extant address signals to control the precharge circuitry wherein the monolithic circuitry comprises: (i) a first p-channel and a first n-channel field effect transistor, each having a gate, drain and source electrode, the gate and drain electrodes of the first p-channel field effect transistor being connected so that that transistor may simulate a resistor and the source and drain electrodes of the first n-channel field effect transistor may simulate a capacitor; (ii) means connecting the biasing voltage to the drain electrode of the first p-channel field effect transistor, the gate and source electrodes of the first p-channel field effect transistor to the gate electrode of the first n-channel field effect transistor and the drain and the source electrodes of the first n-channel transistor to ground to produce, when the biasing voltage is first applied, a time-varying voltage at the gate electrode of the first n-channel field effect transistor, said time-varying voltage changing exponentially from ground potential to a voltage approximating the bias voltage; and (iii) level conversion means, responsive to the level of the time-varying voltage, to produce a voltage essentially at the bias voltage as long as the time-varying voltage is below a predetermined level intermediate ground potential and the biasing voltage and thereafter, as long as the biasing voltage is applied, a voltage at a level approximating ground potential.