Offset problems with AD8054

       Hi. I have the above scheme using the AD8054 op amp. If I ground the JP2 pins I have 0.15 V at the 1, 2 and 3 pins. When I raised pin 3 in the air and connected it directly to GND I still had 0.15V at 1 and 2 pins. If it is not clear in the picture, 2 and 3 pins are inputs and 1 is output. Supply is +/- 5V. What ever voltage there is at JP2 pins there is always an 0.15V extra voltage at the output. Could anyone please help me? Thank you.

  • I'm afraid I really can't read that schematic. Could generate a clearer screen shot and could you annotate it with the voltages measured at each net.

  •         Thank you very much for your quick response. I hope this is a better picture. As I said in my first post, I have a constant offset of 0.15V. Before the +input there is a voltage divider of 1/8. The op amp is connected as a repeater with a negative reaction. Instead of having at the output the voltage divided by 8 I have the voltage divided by 8 plus 0.15V. I must mention that the voltage to be divided is applied between R34 and R38 ,and R37 is taken out of the board. If there is no input applied, there is still 0.15V at 1,2 and 3 pins. When I raised pin 3 in the air and connected it directly to GND I still had 0.15V at 1 and 2 pins. I also tested the op amp off circuit, I connected pins 1 and 2 togheter and I applied 1.45V at pin3. At output I had 0.7V or 2.45 V, and never 1.45.

    Thank you very much.

  • With 0V at the far end of R34, is the voltage at pin 3 0V or is it 0.15V?

    Could you annotate with some actual voltage readings taken with a DMM or oscilloscope?

    What are the measured voltages at pin 4 and pin 11?

    Is the output oscillating In the >10MHz range?

  •        Thank you again for your quick reply.These are the measurements that you asked. At pin 4 there is 5V and at pin 11 there is -5V. At the other +inputs (pins 5,10 and 12) there is no signal and the outputs are: 0.17V at pin 7, 0.16V at pin 8 and 0.16V at pin 14( all -inputs are in short-circuit with the outputs).

         When I applied 1.45V instead of 0V at the far end of R34 there was 0.32V al pins 1,2 and 3.

         I also tried with a brand new AD8054 to test it separately on a test board. I applied 1.47V at pin 3 and at pins 1 and 2, wich were wired together, there was 1.79V.

        Thank you very much.

  • I'm running out of ideas, but what about high frequency oscillations. Can you check with an oscilloscope?