Part Number:TLV2211
Hi,
Using the following circuit to build a board to evaluate the output noise mainly in 0.1~10Hz. Power supply single +3.3V is provided by battery. Finds that R1~R4 resistance has serious affection to circuit for both TLV2211 and OPA333 chips.
When R1~R4 are all 120Ohm, and Rf=220K, the gain is 1666. got the following output noise by clean data capture tool only 2LSB convert to 1.6mVpp noise. it is a little less than simulation result due to avr fitler.
when R1~R4 is all 30Kohm and Rf=20M, the gain is 1333. the output noise is 10LSB , about 8mV. only changed 5 resistors while gain is lower, output noise is 5 times worse.
The circuit has a 16Hz cut off freq LPF, so noise of 0.1~10Hz is definitely dominate. The noise density of 15Kohm(30K||30K) is about 16nV/rtHz, it can be neglected when comparing with op amp's noise density at low freq tens Hz. We got the similar result eitherusing OPA333 or TLV2211. we only see that 20% noise level increase by doing simulation or calculation when comparing the above 2 case. what's the possible cause?
PS, the data capture system runs at 100SPS, and sample-hold time is configured to long enough to eliminate the error.
BRs,
JH