At 03:29 pm 13/03/99 -0500, Sean Breheny wrote:
>Hi all,
>
>In Horowitz and Hill's "Art or Electronics", I see several illustrations of
>very clever little "linear" amplifier configurations using CMOS
>inverters,especially the 74HC04. I have an application (which DOES use a
>PIC,as a freq. counter) where I need to take in a 100mV or so signal from
>about 100Hz or so up to 50MHz and convert it into a 0-5V square wave. There
>is a circuit in H&H which is similar to this and I have been using it as a
>guide,but I am having problems. The basis of the circuit is simply two
>inverters,the output of one connected to the input of the other. The first
>inverter also has a 1Meg ohm feedback resistor across it,and the second one
>doesn't. All other inverters on the chip have their inputs tied high or low.
>
>The behavior I'm seeing is incessant oscillation.

You can generally only use unbuffered CMOS gates in linear mode.  The only
ones I have seen commonly available are 4001UB, 4011UB and 4069UB.

Are you sure your reference specified HC parts?

Mike