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LM6134: OPAMP working

Part Number: LM6134


  I am using LM6134B opamp and doing simple tests. Surprisingly, I found a strange behaviour, for which I am trying to find the reason. I am applying a ramp wave from 0 to VDD at the non-inverting input. I am connecting both VDD and GND. I am keeping both inverting terminal and output of the opamp open. In this set-up, when I increase non-inverting terminal voltage from 0 to VDD i see that the inverting terminal also results in 0 to VDD (more or less). I went through the data sheet ( and there is an internal block diagram in page 14. Can someone explain or convince me what's happening ?

  • Charanraj,

    The input transistors in the diagram have their emitters connected together. This is how the voltage couples from one side to the other. Also the base current from from Q4 goes to base current of Q2 which biases the "floating' input.