analog output question

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Your signal ranges from 5mV to 37mV.

A simple follower-with-gain curcuit will do what you want.

The National Semiconductor LF353 is probably not the amplifier you'd want to use

since the input offset voltage is typically around 5mV with a worst case of 13mV over temperature, and it would require positive and negative voltage supplies in your application.

I'd be more inclined to use the LT1006

which is a single supply op amp with a 50uV input offest specification.

In principle you could probably use a gain of 100 in your application, but you might need to do some heavy low-pass filtering if you did want to run with that kind of gain.

You can build a Sallen and Keyes low pass filter around a single follower with gain, but few text-books analyse the circuit operation at high gain.

The two amplifier version of the circuit - as discussed in Williams and Taylor's "Electronic Filter Design Handbook"

- allows you to choose more or less arbitrary values for the two capacitors involved, which makes the design a lot more practicable. E- mail me - my e-mail address is real - if you want more detail. The dual version of the LT1006 - the LT1013 - would work in such a circuit.

-- Bill Sloman, Nijmegen

Hey, Bill, time's ripe for an ASCII schematic!

There is also this incredibly precision conditioner for which 12-bits is a snap:

On Jan 22, 5:01 pm, snipped-for-privacy@ieee.org wrote: [....]

Add a capacitor across the feedback resistor and you can make the filter better and the capacitor values easy to get ones.

From memory:

------------------------------------ ! ! === 1000p ! 100K ! 100K !

---/\\/\\----+----/\\/\\----+-------!+\\ ! ! ! >------+-----+---Out 0.1 === --!-/ ! ! ! ! GND +----/\\/\\----+ 22K ! ! GND---/\\/\\---------+-----!!----- 0.1 220

This gets quickly to 10 bits, (IIRC) 50mS and reduces the 180Hz by (IIRC) 30dB.