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OPA3693 - 1:2 output using OPA3693

Guru 19775 points
Other Parts Discussed in Thread: OPA3693, OPA3691, OPA3692

Hi Team,

Our customer is considering to use OPA3693 like the schematic below. I think they would not need AC coupling, however, if they prefer to AC couple, can you use below two AC coupling method ?

As there were no TINA TI SPICE model for OPA3693, I had tried simulating with OPA3691/3692 models. As a result, there were an offset to the output that common mode voltage range shifted to the positive voltage from 0V. Is there limitation to the AC coupling cap and the following pull down resistor value ? What would be the recommended value for UXGA video signal ?

Best Regards,


  • Hello,

       The 2nd circuit would have around 1/2 the offset voltage compared to the 1st because in the 1st circuit the bias current from two amplifers is flowing through the 10KOhm resistor. This can results in a maximum of (35uA+35uA)*10K=700mV of offset. The obvious dilemma here is that you want a small resistance (150Ohm) to minimize the offset voltage but that would probably  require a very large cap to maintain the currect cut-off frequency.

      To get maximum signal swing you want the UXGA signal to be ground centered. Another alternative is that if the UXGA signal is riding on a certain offset voltage then you can tie the 300Ohm from the inverting-terminal to the same offset voltage (rather than GND). Note however that the output of the amplifier would also then be riding on the same offset voltage.

     If you cannot apply the offset voltage to the inverting pin: Say the input is at 1.7V common mode, then the output would be at 3.4V common mode. From page 4 of the datasheet (OUTPUT section) the maximum input swing is then 250mV, as this results in a 500mV output swing. Any larger than this then the output would swing greater than 3.4V+0.5V=3.9V which would violate the maximum output swing spec of the amplifier.The input common-mode should not be a limitation for this application because the amplifier is in a G=2 and you would violate the output swing spec before violating the input common-mode spec. Hope this makes sense.

    From a signal swing perspective the OPA3692 and OPA3693 are quite similar to you can use the OPA3692 to verify that the output headroom and input common-mode are within spec.


  • Hi Samir-san,

    Thank you very much for your advice. I understood that the offset had been coming from the bias current. I will input good and bad points of each schematic and let them decide their circuit. Time constant for video application would be generally 470uF x 75Ohm, so when choosing the resistor and AC coupling cap, I believe they should start with the similar time constant.

    Best Regards,