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Power Up One Shot Circuit Using a Subthreshold Current Generator

IP.com Disclosure Number: IPCOM000119848D
Original Publication Date: 1991-Mar-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 2 page(s) / 49K

Publishing Venue

IBM

Related People

Coppens, P: AUTHOR [+5]

Abstract

In CMOS logic circuitry, the latches generally take uncertain values during power-on transition time. This may be hazardous for some applications. Setting latches to desired value requires a single-shot- like circuit which only operates at power-on.

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Power Up One Shot Circuit Using a Subthreshold Current Generator

      In CMOS logic circuitry, the latches generally take
uncertain values during power-on transition time.  This may be
hazardous for some applications. Setting latches to desired value
requires a single-shot- like circuit which only operates at power-on.

      The present disclosure relates to a circuit which meets the
above objective.

      The circuit block diagram is shown in Fig. 1.

      The principle consists of charging a capacitance with a
well-controlled current at power-on time.  Due to a large time
constant, the voltage at node A rises slowly.  The slope of the
signal is much smaller than the slope of the power supply.  This rise
ramp then feeds two inverters which generate a proper voltage step
with appropriate swing. A single-shot is simply derived with this
voltage step.  Since the capacitance has been charged up, the current
flow is cut off.  Therefore, the DC power consumption is null.

      Fig. 2 shows the new circuit schematic.

      The current source described above is implemented with a
subthreshold current generator comprised of devices T1, T2, T3, T4
and T5.  The NEFT has been used to build a few-picofarad-thin oxide
capacitance.  The single-shot circuit comprises an inverter delay
chain and an AND ate.

      Note that the amplitude and the width of the single-shot pulse
can be easily tuned by changing the charging device (T5) size and the
del...