Friday, 11 January 2019

operational amplifier - Negative Voltage Level Shifting to an ADC


I am currently building a project that uses an AD595 analog devices chip to linearize the output of the Thermocouple sensor to 10mv/deg C. This output is to be connected to the ADC input of a Zigbee radio, with a max input of 1.2v. Given that the Zigbee input determines the range, this would achieve a 0-120 degree temperature range. I am now trying to adjust this design to also sense negative temperature.


The AD595 chip can run as dual-supply by connecting -5v and +5v, to give both positive and negative output, however The zigbee radio will not accept a negative voltage input. I believe i now need to place in the design a Non-Inverting Summing Amplifier to "level shift" the range so that "-1.2v - 0v - 1.2v" becomes "0v - 0.6v - 1.2v" and can be interperated by the ADC. I am fairly new to this and i'm not sure where to start, it being especially difficult using a negative voltage.


So far i have used a voltage divider on the output to produce a 5mv/deg C output thus increasing the temperature range to 0-240 deg C. I will have a regulated 5V (ad595), 3.3V (for zigbee) and -5V (for dual) supply.



If anyone could help or point me towards worthwhile resources i would appreciate it a lot.


Thanks.




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