piclist 1998\11\07\142751a >
Thread: Auto range
www.piclist.com/techref/io/sensors.htm?key=rang
picon face BY : Peter L. Peres email (remove spam text)



A small question: How do you handle input voltages that exceed Vdd or go
lower than GND with a tapped resistive divider connected to a multiplexer
?

I was thinking about using a high quality op-amp connected as inverting DC
amp. The input is into the inverting node through a fixed high quality
resistor and the gain is set by a multiplying DAC or resistor ladder and
mux. The reference voltage for ths amp is 1/2 Vref or 1/2 Vdd. This scheme
is applicable for differential input, allows input voltages to exceed Vdd
and go negative etc. The Ri is constant on all the scales. Do you see any
major disadvantage in this ?

Peter

<Pine.LNX.3.95.981107141418.327G-100000@plp4.plp.home.org>

In reply to: <3643BD05.DDCCD693@nb.net>
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