Circuit Design for microvolt range signal

The problem is this : I am looking for low cost circuit design to detect microvolt signal in the range of 0 to 500 microvolt with aaccuracy of 2 microvolt from a set of thermocouples.

I have looked at two designs. First a circuit with an analog filter and 24-bit A/D with a Sigma-Delta filter ( and a low-cost microprocessor) and amplifier. This design is costly due to the high cost of this kind of A/D.

Second design uses a low-cost microcontroller with 10-bit A/D and amplifiers. The amplifiers give noise that is bigger than the signal. The microcontroller does not allow the use of analog filter

 

[jbartos]

Suggestion: Visit

http://www.thomasregister.com

and type Amplifiers: Electronic under Product / Service
that will return 31 companies to inquire about accurate electronic amplifiers

 

[Trex77]

Max... the ckt you are looking for needs several things... good noise reduction (common mode noise), very good DC specs, and some gain to get the signal "up there" for your A/D to work with... all these things can be found in an "instrumentation amp" or IA...

Look to Burr-Brown (now a div. of Texas Instruments), or AD (Analog Devices), or Linear Technologies for stock IA's. All three have web sites. You will want a slow one (under 3Mhz GBW product) that has bipolar inputs (not FET). In the device data sheets you will find recommended ckts for using as a thermocouple amp. Look into also providing a "cold junction" to compensate ambient.