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From: "Ken Taylor"
Subject: Re: CMOS Design Problem
Date: Wed, 13 Nov 2002 16:02:34 +1300
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"Dave Fenner" wrote in message
> "Justin Time" wrote in message
> | I have cascaded a series of D-type flip-flops so the Q output of
> | feeds the Data input of the next. Under carefully controlled
> | conditions it works but has a problem. Waving my hand within 6
> | of the circuit board triggers the flip-flops to a high state.
> | Sometimes one or two... sometimes ten at once. I suspected an
> | inadequately filtered 5 vdc source, but after changing to a 12
> | gel cell battery with a 5 volt voltage regulator, the problem
> | persisted. I experimented with voltages ranging from 2.6 volts to
> | volts without success.
> | I now suspect "noise" from overhead lights or perhaps capacitance
> | straying into the circuit from the wires that connect the circuit
> | Vcc, GND, Clear and Clock.
> | Is there a way to isolate my circuit design from ambient stray
> | capacitance / noise? At this time I have not inserted a clock
> | but have pulsed the input manually in an attempt to pursuede the
> | registers to store the 1 s I have generated into memory.
> | The design works well on paper, but on the bench it is driving me
> | nuts. Any suggestions would be helpful from anyone with CMOS
> | experience. Respectfully, Justin
> Is your entire circuit floating? Tie 0V to earth.
> Dave Fenner.
And tie any unused inputs.
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