Measuring temperature to 24 bits...

Such measurements are not realistic for many reasons, but just because the device is 24 bit doesn't mean that they all need to be used. Personal experience has shown me that the LT2400 can be read temperature to 20 bits with no averaging on a single sample basis with a realy good reference voltage.

Please remember that temperature measurement is an absolute measurement as opossed to a ratiometric one. This means that the resolution and noise is no better than the reference used as well as the linear circuit handling on the PCB etc.

By the way, the LT2400 can have inputs below ground and the lowest voltage available from a K TC is -40 mV. You don't need the offset.

The LT1025 suggested is not for all TC types but is good for those for which it was designed. Since CJC is only needed to compensate for ambient temperatures near the physical space where the TC meets your input connector you may wish to use a simple thermistor circuit and scale it to your needs.

The LT2400 is a great device and easy to interface.

My 2 cents worth
Tom Burdick